GB2565189A - Tin-based langasites activated with europium - Google Patents

Abstract

Europium 3+ activated tin-based langasite compounds of general formula (1): wherein a, b, M, d, A, e and D are as defined in claim 1. Also shown is a process for preparing the compounds by calcination. The compounds may coat or be in a blend another compound. The compounds may be used as (i) luminescent material in fluorescent lamps; (ii) luminescent material in light emitting diodes (LEDs), (iii) scintillation material; or (iv) persistent luminescent material.

Description

Tin-Based Langasites Activated With Europium

Field of the Invention [0001] The present invention relates to a new class of langasite compounds which can be used for various fields of application. The langasite compounds are tin-based langasites which are activated by trivalent europium (Eu³⁺) ions.

[0002] The compounds can be used as (i) luminescent material in fluorescent lamps where the luminescent material is excited by ultraviolet (UV) light which is produced by a gas discharge; as (ii) luminescent material in light emitting diodes (LEDs), especially in phosphor-converted LEDs (pc-LEDs), where the luminescent material is excited by a primary radiation in the UV, violet and/or blue spectral range; as (iii) scintillation material such as e.g. in medical imaging detectors or in detectors for high energy radiation used in high energy physics; or as (iv) persistent luminescent material such as e.g. taggants for security applications, biolabels for medical imaging or temperature sensitive materials in devices for temperature measurement such as e.g. in thermometers.

[0003] The present invention further relates to a process for the preparation of the Eu³⁺-activated tin-based langasites. Moreover, there is provided a blend of luminescent material comprising the Eu³⁺-activated tinbased langasite of the present invention. The present invention further provides for a light source comprising the Eu³⁺-activated tin-based langasite or the blend of luminescent material as light-emitting material. The light source may be a fluorescent lamp or an LED lamp.

[0004] Beyond that, the tin-based langasites of the present invention can be used for a variety of technical applications such as, for example, as a scintillation material in medical imaging detectors or in detectors for high energy radiation. In such detectors the compound is preferably excited by high energy rays selected from X-, α-, β-, γ-rays or combinations thereof. The tin-based langasites of the present invention can be also used as persistent luminescent material for security applications, medical imaging or temperature sensing.

-2State of the Art [0005] For more than 100 years, inorganic luminescent materials have been developed in order to adapt the spectra of emitting display screens, Xray amplifiers and radiation or light sources in such a way that they meet the requirements of the respective field of application in a manner as optimal as possible and at the same time consume as little energy as possible. The type of excitation, i.e. the nature of the primary radiation source, and the requisite emission spectrum are of crucial importance for an appropriate selection of the host lattice and activators of the material.

[0006] Hence, novel luminescent materials for different types of light sources such as e.g. fluorescent lamps or LEDs have been constantly developed in order to further increase the efficiency of the light source, its colour reproduction and stability.

[0007] A fluorescent lamp, which is commonly referred to as a fluorescent tube, is a low-pressure mercury-vapour gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapour which produces short-wave ultraviolet (UV) light that then causes a phosphor coating on the inside of the lamp to glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than incandescent lamps. The typical luminous efficacy of fluorescent lighting systems is 50-100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output.

[0008] For fluorescent lighting applications the photoluminescent properties of the material are relevant. The material needs to be well excitable in the spectral range where the typical gas discharge occurs, such as e.g. at about 250 nm or at about 360 nm. Such excitation is relevant especially for compact fluorescent tubes which are used in modern households.

[0009] Presently, white light emitting LEDs mostly comprise a high brightness blue light emitting semiconductor chip based on (ln,Ga)N [see S. Nakamura et al., Appl. Phys. Lett. 67, p. 1868 (1995)]. The light source works as an efficient pump exciting a luminescent material which returns to its ground state by emitting green, yellow, or red light. Additive colour mixing results in a broadband emission spectrum which is perceived as white light. The principle of this colour conversion process is well-founded

-3in the pronounced Stokes Shift (electron-phonon coupling) between absorption and emission of electromagnetic radiation.

[0010] Already in 1996, Nichia Chemical Industries Ltd. introduced a white light phosphor-converted LED (pc-LED) which uses a luminescent layer comprising Y₃AI₅0i2:Ce (YAG:Ce) phosphor or Y3(Ali._xGa_x)₅0i2:Ce (YAGaG:Ce) phosphor to convert blue light emitted by an (ln,Ga)N LED chip into a broad band yellow emission spectrum with a peak wavelength at about 565 nm. The emission band is sufficiently broad to produce white light in the colour temperature range from about 5,000 to about 8,000 K, and a colour rendering index (CRI) of about 77-85.

[0011] pc-LEDs are currently the prime candidates for solid state lighting (SSL). This is due to their energy saving properties compared to other lighting devices, where a high brightness can be achieved applying small electrical powers. Also their compactness allows for smaller amounts of the luminescent materials to be used compared to e.g. the fluorescent tubes, as well as the final product, the LED lamp, may be used in ways not possible before from architectural point of view. The LED chip, a semiconductor of indium gallium nitride, (ln,Ga)N, emits light in the range of 350 to 490 nm, depending on its chemical composition.

[0012] The requirements put on phosphors used in pc-LEDs are as follows:

1. High color rendering index (CRI) for good light quality,

2. High thermal stability (no significant emission intensity decrease at operating temperatures of T » 150°C or even 200°C),

3. High quantum efficiency (QE) of the phosphor,

4. High chemical stability.

[0013] Binary complementary systems have the advantage that they are capable of producing white light with only one primary light source and - in the simplest case - with only one conversion phosphor. However, improvements in the colour rendering index and the stability of the colour temperature are desirable. For use of a blue-emitting semiconductor as primary light source, binary complementary systems thus require a yellow conversion phosphor in order to reproduce white light. Alternatively, it is possible to use green- and red-emitting conversion phosphors.

[0014] If, as an alternative, the primary light source used is a semiconductor which emits in the violet spectral region or in the near-UV

-4spectrum, either an RGB phosphor mixture or a dichromatic mixture of two conversion phosphors which emit complementary light must be used in order to obtain white light.

[0015] When using a system having a primary light source emitting in the UV or violet region and two complementary conversion phosphors, lightemitting diodes having a particularly high lumen equivalent can be provided. A further advantage of a dichromatic phosphor mixture is the lower spectral interaction and the associated higher package gain.

[0016] In particular, inorganic fluorescent compounds which can be excited in the UV, violet and/or blue spectral region are therefore gaining more and more importance today as conversion phosphors for light sources, in particular for pc-LEDs for the generation of warm-white light. Hence, there is a constant need for novel luminescent materials which may be used as conversion phosphors to be excited in the UV, violet and/or blue spectral region and which emit light in the visible region, in particular in the red spectral region.

[0017] A number of suitable red-emitting phosphors, such as, for example, (Ca,Sr)S:Eu, (Ca,Sr,Ba)2SisN8:Eu and (Ca,Sr)AISiN3:Eu, or mixtures of these phosphors, have already been proposed for this purpose in a large number of patent applications.

[0018] However, a drawback of modern phosphor blends in pc-LEDs is that the red emitting phosphor has a broad emission band, with at least 2530% of the emitted light falling out of the human eye sensitivity, namely at wavelengths above 700 nm. This means that such light does not contribute to the brightness seen by us. Hence, there is a need for much narrower emitters in the red spectral region which show a narrow band emission primarily falling within the wavelength range from about 610 to about 620 nm.

[0019] Another drawback is the rather poor temperature stability of the state-of-the-art red phosphors, as their efficiency falls by about 10% from its room temperature value when the phosphor is operated at high temperatures.

[0020] Hence, it is desirable to find a new material class for the development of high performance light-emitting materials which emit in the red spectral range and have a narrow band emission, preferably in the range from about 610 to about 620 nm, and which show an improved

-5temperature stability so that their efficiency decreases less strongly with increasing temperature. Moreover, it is desirable to find a new material class for the development of high performance light-emitting materials which have high quantum efficiencies and high lumen equivalents. [0021] Beyond that, it would be desirable, if the new material class is also suitable for scintillation. Suitable scintillation materials should have a high density and should be composed of heavy elements, allowing to achieve the so-called high stopping power of the scintillator. The potential of the new material class to provide good scintillators can be evaluated based on the calculated theoretical maximum light yield. It correlates the properties of the luminescent material (e.g. bandgap, quantum efficiency, and trapping efficiency). As a result, the light yield (LY) in photons per megaelectronvolt (ph/MeV) can be obtained. To be commercially relevant, the potential new scintillators has to at least outperform the well-known BGO (Bi₄Ge₃0i2), material of great density and therefore high stopping powder, whose light yield (LY) is 8,200 ph/MeV.

[0022] Finally, it is desirable to find a new material class showing delayed emission which may be used as persistent luminescent material. The capability of a luminescent material to show delayed emission is of interest when it comes to various novel applications, such as e.g. bioimaging, temperature sensing or security applications, to name a few. To evaluate the material’s potential for such applications, one uses thermoluminescence as a tool to investigate the energy trapping properties of a given phosphor. [0023] A possible starting point for the development of novel materials which exhibit the above-mentioned properties might be, for example, langasite compounds. The langasite family is described by the general formula A3BC3D2O14, wherein A denotes a dodecahedral position; B denotes an octahedral position; and C and D denote a tetrahedral position. [0024] Langasites are considered to be very versatile materials, finding their way into numerous industrial and scientific applications, such as e.g. piezoelectric devices, surface-acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters, electro-optic-Q switches, gas sensors and host for laser active media. Also their luminescent properties were investigated. [0025] WO 2007/072129 A1 describes the synthesis of La₃Ga₅SiOi4:Ce and its use as conversion phosphor in LEDs. Some langasites with Cr³⁺ and codoped with Eu³⁺ were presented as efficient afterglow phosphors in

-6WO 2009/134507 A2. However, as can be seen from Table 1 below, using Eu³⁺ in combination with Cr³⁺ is greatly detrimental to the performance of the Eu³⁺ emission resulting in a very low quantum efficiency (QE).

Object of the Invention [0026] In view of the above, it is an object of the present invention to find a new material class which can be used as (i) luminescent material in fluorescent lamps, wherein the luminescent material is excited by UV light which preferably has a wavelength of about 250 nm or about 360 nm, and wherein the luminescent material shows high quantum efficiency under operating conditions.

[0027] Moreover, it is an object of the present invention to provide a new material class which can be used as (ii) luminescent material in LEDs, especially in pc-LEDs, which emits in the red spectral range and has a narrow band emission, preferably in the range from about 610 to about 620 nm, which shows an improved temperature stability so that the light converting efficiency decreases less strongly with increasing temperature, and which provides high quantum efficiencies and high lumen equivalents. This provides the skilled person with a wider choice of suitable phosphors for the preparation of warm white light emitting pc-LEDs.

[0028] Beyond that, it is an object of the present invention to provide a new material class which can be used as (iii) scintillation material, for example, in medical imaging detectors or in detectors for high energy radiation used in high energy physics.

[0029] In addition, it is an object of the present invention to provide a new material class which can be used as (iv) persistent luminescent material, for example, as taggants for security applications, bio-labels for medical imaging or temperature sensitive materials in devices for temperature measurement such as e.g. in thermometers.

[0030] A further object of the present invention is the provision of a preparation process which allows an efficient and simple manufacturing of the compounds belonging to the new material class. Moreover, it is an object of the present invention to provide a blend of light-emitting materials and light sources comprising the new class of luminescent material.

-7Summary of the Invention [0031] Surprisingly, it has been found that the objects of the present invention are achieved by new compounds of the langasite type, where trivalent europium ions (Eu³⁺) are embedded into a tin-based langasite host lattice. Hence, there are provided Eu³⁺-activated tin-based langasite compounds which are represented by general formula (1), (L3i-_a-bEu_aMb)3Ga5-ciAciSn-i-_eD_eO-i4 (1) wherein M is selected from the group consisting of Gd, Lu, Y, Bi, Sc, and combinations thereof;

A is selected from the group consisting of Al, Sc, In, and combinations thereof;

D is selected from the group consisting of Si, Ge, Ti, Zr, Hf, Ga_gE_g, and combinations thereof, wherein E = Nb, Ta or a combination thereof, and g = (1-e) 0.5; and < a < 0.5; 0 < b < 0.25; 0 < d < 2; and 0 < e < 1.

[0032] The present inventors surprisingly found that the above-mentioned tin-based langasites of general formula (1) can be used as (i) luminescent material in fluorescent lamps, since they can be excited by wavelengths of about 360 nm (see Figures 2 and 3 for typical reflection, emission and excitation spectra) and they show high quantum efficiency under operating conditions (see Table 1 below).

[0033] Furthermore, it was surprisingly found that the tin-based langasites of general formula (1) can be used as (ii) luminescent material in LEDs, since they can be excited by light in the wavelength range from about 250 to about 550 nm, preferably from about 250 to 470 nm and more preferably from about 250 to about 420 nm, and they emit red light with a narrow band emission in the wavelength range from about 610 to about 620 nm, preferably at about 615 nm. Efficiencies are listed in Table 1 below, while a typical LED spectrum with indication of the color point in CIE 1931 (inset) is shown in Figure 6. Moreover, the tin-based langasites of general formula (1) show an improved temperature stability, a high quantum efficiency and a high lumen equivalent when used as a conversion phosphor in a LED.

-8[0034] Hence, the new tin-based langasites can be used as luminescent materials in different types of light sources such as e.g. fluorescent lamps or LEDs, preferably in pc-LEDs.

[0035] Moreover, it was surprisingly found that the tin-based langasites of general formula (1) can be used as (iii) scintillation material in medical imaging detectors or in detectors for high energy radiation applications, since they have rather small band gaps with high densities of about 5.8 g/cm³ Additionally, when doped with Eu³⁺ they exhibit high quantum efficiency of luminescence (see Table 1 below). Also the emission matches very well with the commercially available detectors, such as a CCD camera or a photo-diode array or Si-diode.

[0036] The calculated maximum obtainable light yield (LY) is provided in Table 2, taking into account the achieved quantum efficiencies. Light yield (LY) is a measure of efficiency of a scintillator and is expressed in a number of photons emitted over a unit of incoming ionizing radiation (typically over 1 MeV). In Table 2 the values used are band gap (E_g) of the corresponding materials as obtained from the reflection spectra of the undoped respective host lattices, quantum efficiency (QE) having the same meaning as in Table 1 and relating to the number of photons emitted over the number of photons absorbed and giving the material’s efficiency therefore, emission lifetime (t) which is an experimental value obtained telling about the speed at which the excited state decays radiatively. Light yield (LY) for the reference material BGO is a literature value. Scintillation spectra for various Snbased langasites are shown in Figures 7 and 8.

[0037] Beyond that, it was surprisingly found that the tin-based langasites of general formula (1) can be used as (iv) persistent luminescent material. Possible applications are, for example, taggants for security applications, bio-labels for medical imaging or temperature sensitive materials in devices for temperature measurement such as e.g. thermometers. Figures 9 to 11 show typical glow curves recorded for the claimed compounds. The compounds show thermoluminescence after exposure to X-rays, with their glow curves quite similar with the main TL peak localized around 120 to 160°C and with a shoulder around 170 to 200°C. These data show that all the compositions present capability of temporal energy storage at traps of moderate depths. Thus, due to the rather low depths of the traps, right after

-9exposure to X-rays the materials show persistent luminescence at room temperature.

[0038] There is also provided a process for the preparation of the new compounds shown by general formula (1), wherein the process comprises the following steps:

a) preparation of a composition comprising the respective metals contained in the compound according to general formula (1), wherein the metals are provided independently from each other as pure metal elements, oxides, carbonates or halides or mixtures thereof;

b) homogenization of the composition; and

c) calcination of the homogenized composition.

[0039] There is further provided a blend comprising a compound according to general formula (1) and at least one further luminescent material.

[0040] Moreover, there is provided a light source comprising the compound according to general formula (1) or the blend according to the present invention as light-emitting material.

[0041] It is an embodiment of the present invention to use the compound according to general formula (1) as scintillation material in medical imaging detectors or detectors for high energy radiation.

[0042] Finally, it is an embodiment of the present invention to use the compound according to general formula (1) as persistent luminescent material for security applications, medical imaging or temperature sensing. [0043] In view of the inventive embodiments mentioned before, the present invention fulfils all the requirements to solve the technical objects as outlined above.

Brief Description of the Drawings [0044] The invention is illustrated in more detail by Figures 1 to 11 having the following meaning:

Fig. 1 : XRD spectrum of La₃Ga₅SnOi₄:Eu³⁺ langasite.

Fig. 2 : Reflection, emission and excitation spectra of Sn-based langasite La2.4Euo.6Ga5SnOi4.

Fig. 3 : Reflection, emission and excitation spectra of Sn,Hf-based langasite La2.4Euo.6Ga5Sno.9Hfo.1O14.

-10 Fig. 4: T_q plot at 300 nm excitation for La2.4Euo.6Ga₅SnOi4 (solid line) and La2.4Euo.6Ga₅SiOi4 (dotted line).

Fig. 5: T_q plot at 394 nm excitation for La2.4Euo.6Ga₅SnOi4 (solid line) and La2.4Euo.6Ga₅SiOi4 (dotted line).

Fig. 6: Typical LED spectrum and colour point (inset) of La₃Ga₅SnOi4:Eu³⁺.

Fig. 7 : Scintillation spectra of Sn-langasites with various Eu content: solid line: La₃Ga₅SnOi4:Eu³⁺ (20%) dotted line: La3Ga5SnOi4:Eu³⁺ (10%) dashed line: La3Ga₅SnOi4:Eu³⁺ (2%)

Fig. 8 : Scintillation spectra of Sn,Ti- and Sn,Hf-langasites with Eu:

dotted line: La₃Ga₅Tio.5Sno.50i4:Eu³⁺ (20%) solid line: La₃Ga₅Hfo.5Sno.50i4:Eu³⁺ (20%)

Fig. 9 : Glow curve of Sn-langasite with Eu: La₃Ga₅SnOi4:Eu³⁺ (20%).

Fig. 10: Glow curve of Sn,Ti-langasite with Eu: La₃Ga₅Tio.5Sno.50i4:Eu³⁺ (20%).

Fig. 11: Glow curve of Sn,Hf-langasite with Eu: La₃Ga₅Hfo.5Sno.50i4:Eu³⁺ (20%).

Detailed Description of the Invention [0045] The present invention relates to a compound which is represented by general formula (1), (L9i-a-bEUaMb)3Ga5-dAdSn-|.eD_eO-|4 (1) wherein M is selected from the group consisting of Gd, Lu, Y, Bi, Sc, and combinations thereof;

A is selected from the group consisting of Al, Sc, In, and combinations thereof;

D is selected from the group consisting of Si, Ge, Ti, Zr, Hf, Ga_gE_g, and combinations thereof, wherein E = Nb, Ta or a combination thereof, and g = (1-e) 0.5; and < a < 0.5; 0 < b < 0.25; 0 < d < 2; and 0 < e < 1.

[0046] In the above general formula (1) M is a triple charged metal atom M³⁺, A is a triple charged metal atom A³⁺, and D is a quadruple charged metal atom D⁴⁺. La is present as La³⁺. Eu is present as Eu³⁺. Ga is present

-11 as Ga⁵⁺. Sn is present as Sn⁴⁺. Oxygen is present as O²' and compensates for the positive charges in the compound.

[0047] The compounds according to general formula (1) are tin-based langasites which are doped with Eu³⁺. All such compounds have narrow emission bands in the red spectral region between about 610 and about 620 nm, preferably at about 615 nm.

[0048] The compounds according to the invention can usually be excited in the spectral region from about 250 to about 550 nm, preferably from about 250 to about 470 nm, more preferably from about 250 to about 420 nm, and usually emit light with an emission maximum in the red spectral region from about 610 to about 620 nm, preferably at about 615 nm. There is an additional emission in the red spectral region from about 690 nm to about 710 nm.

[0049] In the context of this application, UV light denotes light whose emission maximum is < 400 nm, violet light denotes light whose emission maximum is between 401 and 430 nm, blue light denotes light whose emission maximum is between 431 and 470 nm, cyan-coloured light denotes light whose emission maximum is between 471 and 505 nm, green light denotes light whose emission maximum is between 506 and 560 nm, yellow light denotes light whose emission maximum is between 561 and

575 nm, orange light denotes light whose emission maximum is between

576 and 600 nm and red light denotes light whose emission maximum is between 601 and 700 nm.

[0050] In a preferred embodiment of the invention D is Ge.

[0051] In a preferred embodiment of the invention the following applies to the index a in general formula (1): 0 < a < 0.4, preferably 0 < a < 0.3, and more preferably 0 < a < 0.2.

[0052] In a preferred embodiment of the invention the following applies to the index b in general formula (1): b = 0.

[0053] In a preferred embodiment of the invention the following applies to the index d in general formula (1): d = 0.

[0054] In a preferred embodiment of the invention the following applies to the index e in general formula (1): 0 < e < 0.5, preferably 0 < e < 0.3, more preferably 0 < e < 0.1, and most preferably 0 < e < 0.02.

-12 [0055] In a particular preferred embodiment of the invention, several of the above mentioned preferences apply simultaneously, irrespective of whether they are preferred, more preferred and/or most preferred embodiments.

[0056] Particular preference is therefore given to compounds of the general formula (1) for which the following applies: D is Ge; 0 < a < 0.4; preferably 0 < a < 0.3, more preferably 0 < a < 0.2; b = 0; d = 0; and 0 < e < 0.3, preferably 0 < e < 0.1, more preferably 0 < e < 0.02.

[0057] The compound according to the invention can preferably be coated on its surface with another compound, as described below.

[0058] The present invention furthermore relates to a process for the preparation of a compound according to general formula (1), comprising the following steps:

a) preparation of a composition comprising starting materials of the respective metals contained in the compound of general formula (1), wherein the starting materials are independently selected from pure metal elements, metal oxides, metal carbonates, metal halides and mixtures thereof; and

b) calcination of the composition.

[0059] The compound according to general formula (1) can be prepared by a solid state reaction, a sol-gel method, a combustion method, a precipitation method or combinations thereof. Those skilled in the art aware of these different methods of preparation.

[0060] In step a) the composition is preferably prepared by mixing stoichiometric amounts within 10% deviation of starting materials of the respective metals contained in the compound of general formula (1). The starting materials are provided independently from each other in the form of pure metal elements, metal oxides, metal carbonates, metal halides or mixtures thereof.

[0061] Preferred pure metals are metallic Si, Sn, Ge, Ti, Hf, Zr, Ta, Nb, Ga, La, Lu, Sc, Al, Y, Bi, Gd and In.

[0062] Preferred metal oxides are La₂O₃, Eu₂O₃, M₂O₃ (wherein M = Gd, Lu, Y, Bi and/or Sc), Ga₂O₃, A₂O₃ (wherein A = Al, Sc and/or In), SnO₂, DO₂ (wherein D = Si, Ge, Ti, Zr and/or Hf), Nb₂Os and Ta₂Os.

[0063] Preferred metal carbonates are La₂(CO₃)₃, Eu₂(CO₃)₃, M₂(CO₃)₃ (wherein M = Gd, Lu, Y, Bi and/or Sc), Ga₂(CO₃)₃, A₂(CO₃)₃ (wherein A =

-13 Al, Sc and/or In), Sn(CC>3)2 and D(CC>3)2 (wherein D = Si, Ge, Ti, Zr and/or Hf).

[0064] Preferred metal halides are LaX₃, EuX₃, MX₃ (wherein M = Gd, Lu, Y, Bi and/or Sc), GaX₃, AX₃ (wherein A = Al, Sc and/or In), SnX₄, DX₄ (wherein D = Si, Ge, Ti, Zr and/or Hf), NbX₅ and TaX₅, wherein X = F, Cl and/or Br. Particularly preferred metal halides are LaF₃ and EuF₃.

[0065] The starting materials can be provided in any desired order. They can be provided simultaneously or in any desired sequence. It is preferred that the starting materials are provided in the form of powders or nanopowders.

[0066] The preparation of the composition in step a) is carried out by providing the composition in solid form or as solution of the respective starting materials, preferably as an aqueous solution, more preferably as an acidic aqueous solution. Preferred acids in this regard are nitric acid or sulphuric acid. The solution of the starting materials can be prepared at ambient temperature (25°C) or at elevated temperature, preferably from 50 to 120°C.

[0067] It is preferred that the mixture of starting materials is homogenized before the calcination takes place in step b). This is particularly the case, if the compound according to general formula (1) is prepared by a solid state reaction. The homogenization of the composition is preferably carried out using tubular mixing, centrifugal mixing, planetary ball mixing, or rolling bench mixing apparatus.

[0068] If the compound according to general formula (1) is prepared by a precipitation method from a solution of the starting materials, citric acid or tartaric acid is added to the solution for precipitation. The precipitate is then collected and dried before being submitted to calcination in step b). Drying is preferably carried out at elevated temperature, particularly from 70 to 170°C, more preferably from 110 to 150°C. After the drying a precursor compound is obtained which already contains all metals present in the compound of general formula (1) in the corresponding stoichiometric ratios. The precursor compound is then converted into the compound according to the invention by calcination in step b).

[0069] In a preferred embodiment of the invention there is added at least one flux material to the composition or precipitate prior to the calcination in step b). Preferred flux materials are selected from the group consisting of

-14 B₂O₃, Bi₂O₃, l_i₂O, H3BO3, K₂CO₃, LiCOs, L1HCO3, Na2CO₃, AIF₃-3H₂O, BaF₂, NH₄F, NH4CI, YF₃, K3PO4, (NH₄)₂HPO₄, Li₂SO₄ H₂O, LaNH₄(SO₄)2, (NH₄)₂SO4 and mixtures thereof.

[0070] The calcination in step b) is preferably carried out at temperatures in the range from 100 to 1500°C. In a preferred embodiment of the invention the calcination is carried out in two steps. The first calcination step (pre-calcination) here is preferably carried out in air, N₂, Ar, CO or under vacuum. Preference is given here to a reaction time of 0.1 to 10 h, more preferably 1 to 3 h, and a pre-calcination temperature in the range from 100 to 1350°C. The second calcination step here is preferably carried out in air, Ar, CO or vacuum. Preference is given here to a reaction time of 0.1 to 50 h, more preferably 1 to 30 h, and a calcination temperature in the range from 1200 to 1500°C.

[0071] In a particularly preferred embodiment of the invention, the precalcinated product which is obtained from the first calcination step is cooled and crushed, for example ground in a mortar, before being subjected to the second calcination step.

[0072] The calcination can be carried out in a high-temperature furnace such as for example a chamber furnace. A suitable reaction vessel is, for example, a corundum crucible with a lid.

[0073] In a further embodiment the compound according to the invention can be coated. Suitable for this purpose are all coating methods as known to the person skilled in the art and used for luminescent materials such as e.g. phosphors. Suitable materials for the coating are, in particular, metal oxides and nitrides, in particular alkaline-earth metal oxides, such as AI₂O₃, and alkaline-earth metal nitrides, such as AIN, as well as SiO₂. The coating can be carried out here, for example, by fluidised-bed methods or by wetchemical methods. Suitable coating methods are disclosed, for example, in JP 04-304290, WO 91/10715, WO 99/27033, US 2007/0298250, WO 2009/ 065480, WO 2010/075908 and US 2012/0199793 A1. In particular, chemical vapour deposition or atomic layer deposition methods are suitable for coating of the compounds of the present invention.

[0074] The aim of the coating can on the one hand be higher stability of the phosphors, for example to air or moisture. However, the aim may also be an improved coupling in and out of light through a suitable choice of the surface of the coating and the refractive indices of the coating material.

-15 [0075] The present invention still furthermore relates to a blend comprising a compound according to the invention and at least one further luminescent material. It is preferred that the blend comprises one, two, three, four or five or more further luminescent materials. Suitable further luminescent materials are preferably phosphor materials (conversion phosphors) or quantum materials. It is preferred that the phosphor materials to be used as further luminescent materials are different from the compound according to the invention.

[0076] It is particularly preferred that the blend comprises at least one further luminescent material having a light emission which is complementary to the light emission from the compound according to the invention.

[0077] Suitable phosphor materials which may be used as further luminescent material in the blend of the present invention are familiar to the person skilled in the art such as, for example: Ba₂SiO4:Eu²⁺, BaSi2N2O2:Eu,BaSi2O5:Pb²⁺, Ba3SisOi2N₂:Eu, Ba_xSri._xF₂:Eu²⁺ (where 0 <x < 1), BaSrMgSi2O7:Eu²⁺, BaTiP2O₇, (Ba,Ti)₂P₂O₇:Ti, BaY₂F₈:Er³⁺,Yb⁺, Be2SiO4:Mn²⁺, Bi4Ge30i₂, CaAI₂O4:Ce³⁺, CaLa4O7:Ce³⁺, CaAI2O4:Eu²⁺, CaAI2O4:Mn²⁺, CaAI4O₇:Pb²⁺,Mn²⁺, CaAI2O4:Tb³⁺, Ca3AI₂Si30i₂:Ce³⁺, Ca3AI2Si30i2:Ce³ , Ca3AI₂Si₃O,₂:Eu² , Ca2B5O9Br:Eu² , CasBsOgCLEu²*, 032Β₅0₉0Ι:Ρό²⁺, CaB2O4:Mn²⁺, 032Β₂0₅:Μη²⁺, CaB2O4:Pb²⁺, CaB2P2O₉:Eu²⁺, Ca5B2SiOio:Eu³⁺, Cao.5Bao.5Ali2Oig:Ce³⁺,Mn²⁺, Ca2Ba3(PO4)3CI:Eu²⁺, CaBr2:Eu²⁺ in SiO2, CaCI2:Eu²⁺ in SiO2, CaCI₂:Eu²⁺,Mn²⁺ in SiO2, CaF2:Ce³⁺, CaF2:Ce³⁺,Mn²⁺, CaF2:Ce³⁺,Tb³⁺, CaF2:Eu²⁺, CaF2:Mn²⁺, CaGa2O4:Mn²⁺, CaGa4O7:Mn²⁺, CaGa2S4:Ce³⁺, CaGa2S4:Eu²⁺, CaGa2S4:Mn²⁺, CaGa2S4:Pb²⁺, CaGeO3:Mn²⁺, Cal2:Eu²⁺ in SiO2, Cal₂:Eu²⁺,Mn²⁺ in SiO2, CaLaBO4:Eu³⁺, CaLaB3O₇:Ce³⁺,Mn²⁺, Ca2La2BO6.5:Pb² , Ca2MgSi₂O₇, Ca₂MgSi₂O₇:Ce³ , CaMgSi2O6:Eu² , Ca3MgSi₂O8:Eu²⁺, Ca2MgSi2O7:Eu²⁺, CaMgSi2O6:Eu²⁺,Mn²⁺, Ca2MgSi2O7:Eu²⁺,Mn²⁺, CaMoO4, CaMoO₄:Eu³⁺, CaO:Bi³⁺, CaO:Cd²⁺, CaO:Cu⁺, CaO:Eu³⁺, CaO:Eu³⁺, Na⁺, CaO:Mn²⁺, CaO:Pb²⁺, CaO:Sb³⁺, CaO:Sm³⁺, CaO:Tb³⁺, CaO:TI, CaO:Zn²⁺, Ca2P2O7:Ce³⁺, a-Ca3(PO₄)₂:Ce³⁺, B-Ca3(PO4)2:Ce³⁺, Ca5(PO₄)3CI:Eu²⁺, 035(Ρ04)30Ι:Μη²⁺, Ca5(PO₄)3CI:Sb³⁺, Ca5(PO4)3CI:Sn²⁺, Mn²⁺, Ca5(PO₄)3F:Mn²⁺, Ca5(PO4)3F:Sb³⁺, Ca5(PO₄)3F:Sn²⁺, a-Ca3(PO4)2:Eu²⁺, B-Ca3(PO₄)₂:Eu²⁺, Ca₂P₂O₇:Eu²⁺,

-16 Ca₂P₂O₇:Eu²⁺,Mn²⁺, CaR2O6:Mn²⁺, a-Ca3(PO₄)2:Sn²⁺, B-Ca3(PO4)2:Sn²⁺, B-Ca2P₂O₇:Sn,Mn, a-Ca₃(PO₄)₂:Tr, CaS:Bi³⁺, CaS:Bi³⁺,Na, CaS:Ce³⁺, CaS:Eu²⁺, CaS:Cu⁺,Na⁺, CaS:l_a³⁺, CaS:Mn²⁺, CaSO4:Bi, CaSO4:Ce³⁺, CaSO4:Ce³⁺,Mn²⁺, CaSO4:Eu²⁺, CaSO4:Eu²⁺,Mn²⁺, CaSO4:Pb²⁺, CaS:Pb²⁺, CaS:Pb²⁺,CI, CaS:Pb²⁺,Mn²⁺, CaS:Pr³⁺,Pb²⁺,CI, CaS:Sb³⁺, CaS:Sb³⁺,Na, CaS:Sm³⁺, CaS:Sn²⁺, CaS:Sn²⁺,F, CaS:Tb³⁺, CaS:Tb³⁺,CI, CaS:Y³⁺, CaS:Yb²⁺, CaS:Yb²⁺,CI, CaSc2O₄:Ce,Ca₃(Sc,Mg)₂Si₃Oi₂:Ce,CaSiO₃:Ce³⁺, Ca3SiO4CI2:Eu²⁺, Ca3SiO₄CI₂:Pb²⁺, CaSiO3:Eu²⁺, CaSiO3:Mn²⁺,Pb, CaSiO3:Pb²⁺, CaSiO3:Pb²⁺,Mn²⁺, CaSiO3:Ti⁴⁺, CaSr2(PO₄)₂:Bi³⁺, 3-(Ca,Sr)3(PO4)2:Sn²⁺Mn²⁺, CaTi0.₉AI₀.iO₃:Bi³⁺, CaTiO3:Eu³⁺, CaTiO3:Pr³⁺, Ca5(VO4)3CI, CaWO4, CaWO4:Pb²⁺, CaWO4:W, Ca₃WO₆:U, CaYAIO₄:Eu³⁺, CaYBO4:Bi³⁺, CaYBO4:Eu³⁺, CaYB0.8O3.7:Eu³⁺, CaY2ZrO₆:Eu³⁺, (Ca,Zn,Mg)3(PO4)2:Sn, (Ce,Mg)BaAlnOi8:Ce, (Ce,Mg)SrAlnOi8:Ce, CeMgAlnOi9:Ce:Tb, Cd2B60n:Mn²⁺, CdS:Ag⁺,Cr, CdS:ln, CdS:ln, CdS:ln,Te, CdS:Te, CdWO4, CsF, Csl, Csl:Na⁺, Csl:TI, (ErCI3)o.25(BaCI2)o.75, GaN:Zn, Gd3GasOi2:Cr³⁺, Gd3Ga5O-i2:Cr,Ce, GdNbO₄:Bi³⁺, Gd2O2S:Eu³⁺, Gd2O₂Pr³⁺, Gd2O2S:Pr,Ce,F, Gd2O2S:Tb³⁺, Gd2SiO₅:Ce³⁺, KAIhOi7:TI⁺, KGanOi7:Mn²⁺, K2La2Ti3Oi0:Eu, KMgF3:Eu²⁺, KMgF3:Mn²⁺, K2SiF6:Mn⁴⁺, LaAI3B₄0i₂:Eu³⁺, LaAIB2O6:Eu³⁺, LaAIO3:Eu³⁺, LaAIO3:Sm³⁺, LaAsO4:Eu³⁺, LaBr3:Ce³⁺, LaBO3:Eu³⁺, LaCI3:Ce³⁺, La2O₃:Bi³⁺, LaOBr:Tb³⁺, LaOBr:Tm³⁺, LaOCI:Bi³⁺, LaOCI:Eu³⁺, LaOF:Eu³⁺, La2O3:Eu³⁺, La2O₃:Pr³⁺, La2O2S:Tb³⁺, LaPO4:Ce³⁺, LaPO4:Eu³⁺, LaSiO3CI:Ce³⁺, LaSiO3CI:Ce³⁺,Tb³⁺, LaVO4:Eu³⁺, La2W30i2:Eu³⁺, LiAIF4:Mn²⁺, LiAI5O8:Fe³⁺, LiAIO2:Fe³⁺, LiAIO2:Mn²⁺, LiAI5O₈:Mn²⁺, Li2CaP2O7:Ce³⁺,Mn²⁺, LiCeBa4Si₄0i₄:Mn²⁺, LiCeSrBa3Si40i4:Mn²⁺, LilnO2:Eu³⁺, LilnO2:Sm³⁺, Lil_aO2:Eu³⁺, LuAIO3:Ce³⁺, (Lu,Gd)2SiO₅:Ce³⁺, Lu2SiO5:Ce³⁺, Lu2Si₂O₇:Ce³⁺, LuTaO4:Nb⁵⁺, Lui_xY_xAIO₃:Ce³⁺ (where 0<x< 1), (Lu,Y)3(AI,Ga,Sc)5Oi2:Ce,MgAI2O4:Mn²⁺, MgSrAI10Oi₇:Ce, MgB₂O₄:Mn²⁺, MgBa2(PO4)2:Sn²⁺, MgBa2(PO₄)₂:U, MgBaP₂O₇:Eu²⁺, MgBaP2O7:Eu²⁺,Mn²⁺, MgBa3Si₂O₈:Eu²⁺, MgBa(SO4)2:Eu²⁺, Mg3Ca₃(PO₄)₄:Eu²⁺, MgCaP2O7:Mn²⁺, Mg2Ca(SO₄)₃:Eu²⁺, Mg2Ca(SO4)3:Eu²⁺,Mn², MgCeAlnOi₉:Tb³⁺, Mg4(F)GeO6:Mn²⁺, Mg4(F)(Ge,Sn)O₆:Mn²⁺, MgF2:Mn²⁺, MgGa2O₄:Mn²⁺, Mg8Ge20nF2:Mn⁴⁺, MgS:Eu²⁺, MgSiO3:Mn²⁺, Mg2SiO4:Mn²⁺, Mg3SiO₃F₄:Ti⁴⁺, MgSO4:Eu²⁺, MgSO4:Pb²⁺, MgSrBa2Si2O7:Eu²⁺, MgSrP2O₇:Eu²⁺, MgSr5(PO4)4:Sn²⁺, MgSr3Si₂O₈:Eu²⁺,Mn²⁺, Mg2Sr(SO4)3:Eu²⁺, Mg2TiO₄:Mn⁴⁺, MgWO₄,

-17 MgYBO₄:Eu³⁺, Na3Ce(PO4)2:Tb³⁺, Nai.23Ko.₄₂Euo.i2TiSi₄Oii:Eu³⁺, Nai.23Ko.42Euo.i2TiSi50i3 xH20:Eu³⁺, Nai.29Ko.46Ero.o8TiSi₄On:Eu³⁺, Na2Mg3Al2Si20-io:Tb, Na(Mg2-xMnx)LiSi4OioF2:Mn (where 0 < x < 2), NaYF4:Er³⁺, Yb³⁺, NaYO2:Eu³⁺, P46(70%) + P47 (30%), 3-SiAION:Eu,SrAli2Oi9:Ce³⁺, Mn²⁺, SrAI2O₄:Eu²⁺, SrAI4O7:Eu³⁺, SrAli20i₉:Eu²⁺, SrAI2S4:Eu²⁺, Sr2B₅O₉CI:Eu²⁺, SrB4O7:Eu²⁺(F,CI,Br), SrB4O₇:Pb²⁺, SrB4O7:Pb²⁺, Mn²⁺, SrB80i₃:Sm²⁺, SrxBayClzAI2O4.z/2: Mn²⁺, Ce³⁺, SrBaSiO4:Eu²⁺, (Sr,Ba)3SiO5:Eu,(Sr,Ca)Si2N2O2:Eu, Sr(CI,Br,l)2:Eu²⁺ in S1O2, SrCI2:Eu²⁺ in S1O2, Sr5CI(PO4)3:Eu, SrwFxB4O6.5:Eu²⁺, SrwF_xB_yO_z:Eu²⁺,Sm²⁺, SrF2:Eu²⁺, SrGai20i₉:Mn²⁺, SrGa2S4:Ce³⁺, SrGa2S₄:Eu²⁺, SrGa2S4:Pb²⁺, Srln2O₄:Pr³⁺, Al³⁺, (Sr,Mg)3(PO4)2:Sn, SrMgSi2O6:Eu²⁺, Sr2MgSi2O₇:Eu²⁺, Sr3MgSi2O8:Eu²⁺, SrMoO4:U, SrO-3B₂O₃:Eu²⁺,CI, 3-SrO-3B2O3:Pb²⁺, 3-SrO-3B2O₃ :Pb²⁺,Mn²⁺, a-SrO-3B2O3:Sm²⁺, Sr6P5B02o:Eu,Sr₅(P0₄)3CI:Eu²⁺, Sr5(PO4)3CI:Eu²⁺,Pr³⁺, Sr5(PO₄)₃CI:Mn²⁺, Sr5(PO4)3CI:Sb³⁺,Sr2P2O₇:Eu²⁺, 3-Sr3(PO4)2:Eu²⁺, Sr5(PO₄)3F:Mn²⁺,Sr5(PO4)3F:Sb³⁺, Sr5(PO₄)₃F:Sb³⁺,Mn²⁺, Sr5(PO4)3F:Sn²⁺, Sr2P₂O₇:Sn²⁺, 3-Sr3(PO4)2:Sn²⁺, 3-Sr3(PO₄)₂:Sn²⁺,Mn²⁺(AI), SrS:Ce³⁺, SrS:Eu²⁺, SrS:Mn²⁺, SrS:Cu⁺,Na, SrSO4:Bi, SrSO4:Ce³⁺, SrSO4:Eu²⁺, SrSO4:Eu²⁺,Mn²⁺, Sr5Si₄Oi₀CI₆:Eu²⁺, Sr2SiO4:Eu²⁺, SrTiO3:Pr³⁺, SrTiO3:Pr³⁺,AI³⁺,SrY2O₃:Eu³⁺, ThO2:Eu³⁺, ThO2:Pr³⁺, ThO2:Tb³⁺, YAI3B₄0i₂:Bi³⁺, YAI3B40i2:Ce³⁺, YAI3B₄0i₂:Ce³⁺,Mn, YAI3B40i2:Ce³⁺,Tb³⁺, YAI3B₄0i₂:Eu³⁺, YAI3B40i2:Eu³⁺,Cr³⁺, YAI3B₄Oi₂:Th⁴⁺,Ce³⁺,Mn²⁺, YAIO3:Ce³⁺, Y3AI₅0i₂:Ce³⁺, Υ3ΑΙ5Οι2:Ογ³⁺, YAIO3:Eu³⁺, Y3AI50i2:Eu^3r, Y4AI₂O₉:Eu³⁺, Y3AI50i2:Mn⁴⁺, YAIO3:Sm³⁺, YAIO3:Tb³⁺, Y3AI₅0i₂:Tb³⁺, YAsO4:Eu³⁺, YBO3:Ce³⁺, YBO3:Eu³⁺, YF3:Er³⁺,Yb³⁺, YF3:Mn²⁺, YF3:Mn²⁺,Th⁴⁺, YF3:Tm³⁺,Yb³⁺, (Y,Gd)BO3:Eu, (Y,Gd)BO₃:Tb, (Y,Gd)₂O₃:Eu³⁺, Y134Gdo.6o03(Eu,Pr), Y2O3:Bi³⁺, YOBr:Eu³⁺, Y2O₃:Ce, Y₂O₃:Er³⁺, Y2O3:Eu³⁺, Y2O₃:Ce³⁺,Tb³⁺, YOCI:Ce³⁺, YOCI:Eu³⁺, YOF:Eu³⁺, YOF:Tb³⁺, Y2O3:Ho³⁺, Y2O₂S:Eu³⁺, Y2O2S:Pr³⁺, Y2O₂S:Tb³⁺, Y2O3:Tb³⁺, YPO4:Ce³⁺, YPO4:Ce³⁺,Tb³⁺, YPO4:Eu³⁺, YPO4:Mn²⁺,Th⁴⁺, YPO4:V⁵⁺, Y(P,V)O4:Eu, Y2SiO5:Ce³⁺, YTaO4, YTaO₄:Nb⁵⁺, YVO4:Dy³⁺, YVO4:Eu³⁺, ZnAI2O4:Mn²⁺, ZnB2O₄:Mn²⁺, ZnBa2S3:Mn²⁺, (Zn,Be)2SiO₄:Mn²⁺, Zno.4Cdo.6S:Ag, Zno.6Cdo.4S:Ag, (Zn,Cd)S:Ag,CI, (Zn,Cd)S:Cu, ZnF2:Mn²⁺, ZnGa2O₄, ZnGa₂O₄:Mn²⁺, ZnGa2S4:Mn²⁺, Zn2GeO₄:Mn²⁺, (Zn,Mg)F2:Mn²⁺, ZnMg2(PO₄)₂:Mn²⁺, (Zn,Mg)₃(PO₄)₂:Mn²⁺, ZnO:AI³⁺,Ga³⁺, ZnO:Bi³⁺, ZnO:Ga³⁺, ZnO:Ga, ZnO-CdO:Ga, ZnO:S, ZnO:Se, ZnO:Zn, ZnS:Ag⁺,Cl·,

-18 ZnS:Ag,Cu,CI, ZnS:Ag,Ni, ZnS:Au,ln, ZnS-CdS (25-75), ZnS-CdS (50-50), ZnS-CdS (75-25), ZnS-CdS:Ag,Br,Ni, ZnS-CdS:Ag⁺,CI, ZnS-CdS:Cu,Br, ZnS-CdS:Cu,l, ZnS:Cl·, ZnS:Eu²⁺, ZnS:Cu, ZnS:Cu⁺,AI³⁺, ZnS:Cu⁺,Cl·, ZnS:Cu,Sn, ZnS:Eu²⁺, ZnS:Mn²⁺, ZnS:Mn,Cu, ZnS:Mn²⁺,Te²⁺, ZnS:P, ZnS:P³',Cl·, ZnS:Pb²⁺, ZnS:Pb²⁺,Cl·, ZnS:Pb,Cu, Zn3(PO4)2:Mn²⁺, Zn2SiO₄:Mn²⁺, Zn2SiO4:Mn²⁺,As⁵⁺, Zn2SiO₄:Mn,Sb₂O₂, Zn₂SiO₄:Mn²⁺,P, Zn2SiO4:Ti⁴⁺, ZnS:Sn²⁺, ZnS:Sn,Ag, ZnS:Sn²⁺,l_i⁺, ZnS:Te,Mn, ZnSZnTe:Mn²⁺, ZnSe:Cu⁺,CI und ZnWO4.

[0078] The compound according to the invention exhibits, in particular, advantages when mixed with further phosphors of other fluorescence colours or on use in LEDs together with phosphors of this type. The compounds according to the invention are preferably employed together with green-emitting phosphors as well as with blue emitting phosphors when UV or violet excitation is used. It has been found that, in particular on combination of the compounds according to the invention with greenemitting phosphors, optimisation of lighting parameters for white LEDs succeeds particularly well.

[0079] Corresponding green-emitting phosphors and blue emitting phosphors are known to the person skilled in the art or can be selected by the person skilled in the art from the list given above. Particularly suitable red-emitting phosphors here are (Sr,Ba)₂SiO₄:Eu, (Sr,Ba)3SiOs:Eu, (Sr,Ca)Si₂N₂O₂:Eu, BaSi₂N₂O₂:Eu, (Lu,Y)₃(AI,Ga,Sc)₅0i₂:Ce, p-SiAION:Eu, CaSc₂O₄:Ce, CaSc₂O₄:Ce,Mg, Ba₃Si60i₂N₂:Eu and Ca₃(Sc,Mg)₂Si30i₂:Ce. Particular preference is given to Ba₃Si₆0i₂N₂:Eu and Ca₃(Sc,Mg)₂Si30i₂:Ce.

[0080] In still a further embodiment of the invention, it is preferred for the phosphors to be arranged on the primary light source in such a way that the red-emitting phosphor is essentially hit by the light from the primary light source, while the green-emitting phosphor is essentially hit by the light that has already passed through the red-emitting phosphor or has been scattered thereby. This can be achieved by installing the red-emitting phosphor between the primary light source and the green-emitting phosphor.

[0081] Suitable quantum materials which may be used as further luminescent material in the blend of the present invention are familiar to the person skilled in the art. Quantum materials are semiconductor

-19 nanoparticles with physical properties that are widely tuneable by controlling particle size, composition and shape.

[0082] Among the most evident size dependent property of this material class is the tunable fluorescence emission. The tuneability is afforded by the quantum confinement effect, where reducing particle size leads to a “particle in a box” behavior, resulting in a blue shift of the band gap energy and hence the light emission.

[0083] For example, in this manner, the emission of CdSe nanocrystals can be tuned from 660 nm for particles of diameter of ~ 6.5 nm, to 500 nm for particles of diameter of ~2 nm. Similar behavior can be achieved for other semiconductors when prepared as nanocrystals allowing for broad spectral coverage from the UV (using ZnSe, CdS for example) throughout the visible (using CdSe, InP for example) to the near-IR (using InAs for example).

[0084] Suitable semiconductor materials are preferably selected from groups ll-VI, lll-V, IV-VI or l-lIl-VI₂ or any desired combination of one or more thereof. For example, the semiconductor material may be CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, GaAs, GaP, GaAs, GaSb, GaN, HgS, HgSe, HgTe, InAs, InP, InSb, AlAs, AIP, AlSb, Cu₂S, Cu₂Se, CuGaS₂, CuGaSe₂, CulnS₂, CulnSe₂, Cu₂(lnGa)S4, AglnS₂, AglnSe₂, Cu₂(ZnSn)S4, alloys thereof and mixtures thereof.

[0085] The semiconductor nanoparticle can have any desired symmetrical or asymmetrical geometrical shape, and non-restrictive examples of possible shapes are elongate, round, elliptical, pyramidal, etc.. A specific example of a semiconductor nanoparticle is an elongate nanoparticle, which is also called a nanorod and is made from a semiconducting material. [0086] Further semiconductor nanorods which can be used are those having a metal or metal-alloy region on one or both ends of the respective nanorod. Examples of such elongate semiconductor/metal nanoparticles and the production thereof are described in WO 2005/075339, the disclosure content of which is incorporated herein by way of reference. Other possible semiconductor/metal nanoparticles are shown in WO 2006/134599, the disclosure content of which is incorporated herein by way of reference.

[0087] Furthermore, semiconductor nanoparticles in a core/shell configuration or a core/multishell configuration are known. These are

-20 discrete semiconductor nanoparticles which are characterised by a heterostructure, in which a core comprising one type of material is covered with a shell comprising another material. In some cases, the shell is allowed to grow on the core, which serves as seed core. The core/shell nanoparticles are then also referred to as seeded nanoparticles. The expression seed core or core relates to the innermost semiconductor material present in the heterostructure. Known semiconductor nanoparticles in core/shell configuration are shown, for example, in EP 2 528 989 B1, the contents of which are incorporated into the present description in their totality by way of reference.

[0088] The semiconductor nanoparticles may be also located on the surface of a non-activated crystalline material (i.e. matrix material) such as described in WO 2017/041875 A1, the disclosure of which is hereby incorporated by reference.

[0089] Suitable non-activated crystalline materials are matrix materials of an inorganic phosphor. Preferred non-activated crystalline materials are selected from non-activated crystalline metal oxides, non-activated crystalline silicates and halosilicates, non-activated crystalline phosphates and halophosphates, non-activated crystalline borates and borosilicates, non-activated crystalline aluminates, gallates and alumosilicates, nonactivated crystalline molybdates and tungstates, non-activated crystalline sulfates, sulfides, selenides and tellurides, non-activated crystalline nitrides and oxynitrides, non-activated crystalline SiAIONs and other non-activated crystalline materials, such as non-activated crystalline complex metaloxygen compounds, non-activated crystalline halogen compounds and nonactivated crystalline oxy compounds, such as preferably oxysulfides or oxychlorides.

[0090] If the compounds or blends according to the invention are employed in small amounts, they already give rise to good LED qualities. The LED quality is described here by means of conventional parameters, such as, for example, the colour rendering index (CRI), the correlated colour temperature (CCT), lumen equivalent or absolute lumen, or the colour point in CIE x and y coordinates.

[0091] The colour rendering index (CRI) is a dimensionless lighting quantity, familiar to the person skilled in the art, which compares the colour

-21 reproduction faithfulness of an artificial light source with that of sunlight or filament light sources (the latter two have a CRI of 100).

[0092] The correlated colour temperature (CCT) is a lighting quantity, familiar to the person skilled in the art, with the unit kelvin. The higher the numerical value, the higher the blue content of the light and the colder the white light from an artificial radiation source appears to the observer. The CCT follows the concept of the black body radiator, whose colour temperature describes the so-called Planck curve in the CIE diagram.

[0093] The lumen equivalent is a lighting quantity, familiar to the person skilled in the art, with the unit Im/W which describes the magnitude of the photometric luminous flux in lumens of a light source at a certain radiometric radiation power with the unit watt. The higher the lumen equivalent, the more efficient a light source.

[0094] The lumen is a photometric lighting quantity, familiar to the person skilled in the art, which describes the luminous flux of a light source, which is a measure of the total visible radiation emitted by a radiation source. The greater the luminous flux, the brighter the light source appears to the observer.

[0095] CIE x and CIE y stand for the coordinates in the standard CIE colour chart (here standard observer 1931), familiar to the person skilled in the art, by means of which the colour of a light source is described.

[0096] All the quantities mentioned above can be calculated from the emission spectra of the light source using methods known to the person skilled in the art.

[0097] The present invention furthermore relates to a light source comprising the compound or blend according to the present invention as light-emitting material.

[0098] In a preferred embodiment, the light source is a fluorescent lamp, wherein the light-emitting material is excited by a gas discharge, preferably by a Hg gas discharge of 254 nm or 360 nm.

[0099] In an alternative preferred embodiment, the light source is an LED, especially an pc-LED, comprising at least one primary light source emitting UV, violet and/or blue light, wherein the light-emitting material converts the light of the primary light source into light having a longer wavelength, preferably into red light.

-22 [00100] Preferably, the primary light source is a semiconductor light emitting diode (SLED) or a laser diode (LD) emitting UV, violet and/or blue light. More preferably, the primary light source is a (SLED). The primary light source preferably has a peak wavelength in the spectral range from about 250 to about 550 nm, more preferably from about 250 to about 470 nm, and most preferably from about 250 to about 420 nm.

[00101] A semiconductor light emitting diode (SLED), forming a first group of suitable primary light sources, is a two-lead semiconductor light source. It is a p-n junction diode, which emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect called electroluminescence, and the colour of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/lnGaN, also use sapphire substrate. The structure and mode of operation of SLEDs are known to the person skilled in the art.

[00102] In a preferred embodiment the SLED comprises a luminescent indium aluminium gallium nitride, preferably of the formula InjGajAlkN, wherein 0 < i, 0 < j, 0 < k, and i + j + k = 1, or a luminescent arrangement based on ZnO, TCO (transparent conducting oxide), ZnSe or SiC.

[00103] A laser diode, or LD also known as injection laser diode or ILD, is an electrically pumped semiconductor laser in which the active laser medium is formed by a p-n junction of a semiconductor diode similar to that found in a semiconductor light emitting diode. The structure and mode of operation of LDs are known to the person skilled in the art. The laser diode is the most common type of laser produced with a wide range of uses that include fibre optic communications, barcode readers, laser pointers, CD/DVD/Blu-Ray disc reading and recording, laser printing, laser scanning and increasingly directional lighting sources.

[00104] The compound or blend according to the invention can be in the form of loose material, powder material, thick or thin layer material or selfsupporting material, preferably in the form of a film. It may furthermore be embedded in an encapsulation material. The compound or blend according

-23 to the invention can either be dispersed in a resin (e.g. an epoxy resin, silicone resin, a polysil(ox)azane resin, etc.) as encapsulation material, or, in the case of suitable size ratios, arranged directly on the primary light source or alternatively arranged remote therefrom, depending on the application (the latter arrangement also includes remote phosphor technology). The advantages of remote phosphor technology are known to the person skilled in the art and are revealed, for example, by the following publication: Japanese J. of Appl. Phys. Vol. 44, No. 21 (2005), L649-L651. [00105] In a further embodiment, it is preferred for the optical coupling between the phosphor and the primary light source to be achieved by a light-conducting arrangement. This makes it possible for the primary light source to be installed at a central location and to be optically coupled to the phosphor by means of light-conducting devices, such as, for example, optical fibres. In this way, it is possible to achieve lamps adapted to the lighting wishes which merely consist of one or more different phosphors, which can be arranged to form a light screen, and an optical waveguide, which is coupled to the primary light source. In this way, it is possible to place a strong primary light source at a location which is favourable for electrical installation and to install lamps comprising phosphors which are coupled to the optical waveguides at any desired locations without further electrical cabling, but instead only by laying optical waveguides.

[00106] The particle size of the compounds according to the invention for use in LEDs is usually between 50 nm and 30 pm, preferably between 1 pm and 20 pm.

[00107] For use in LEDs, the compounds according to the invention can also be converted into any desired outer shapes, such as e.g. spherical particles, platelets, filaments and structured materials and ceramics (i.e. shaped phosphor bodies). The person skilled in the art is familiar with the production and use of such shaped phosphor bodies.

[00108] Moreover, the compound according to the present invention may be used as scintillation material in medical imaging detectors or detectors for high energy radiation. Preferably, in such medical imaging detectors or detectors for high energy radiation the compound of the present invention is excited by high energy rays selected from X-, α-, β-, γ-rays or a combination thereof.

-24 [00109] Beyond that, the compound according to the present invention may be used as luminescent material for security applications, medical imaging or temperature sensing. Preferred security applications are e.g. those used in banknotes. Medical imaging may be preferably carried out in a way where the material is exposed to high energy radiation such as e.g. X-rays and generates red photons around 615 nm that can be well detected by e.g. a CCD camera or a Si-diode. An example of such a system might be e.g. a computer tomograph. Temperature sensing may be preferably carried out in a way where the material’s well defined and highly tuneable depending on composition change in luminescence output with temperature is exploited.

[00110] All variants of the invention described here can be combined with one another so long as the respective embodiments are not mutually exclusive. In particular, it is an obvious operation, on the basis of the teaching of this specification, as part of routine optimisation, precisely to combine various variants described here in order to obtain a specific particularly preferred embodiment.

[00111] The following examples are intended to illustrate the present invention and show, in particular, the result of such illustrative combinations of the invention variants described. However, they should in no way be regarded as limiting, but instead are intended to stimulate generalisation. [00112] All compounds or components which are used in the preparations are either known and commercially available or can be synthesised by known methods. The temperatures indicated in the examples are always in °C. It furthermore goes without saying that, both in the description and also in the examples, the amounts of the constituents used in the compositions always add up to a total of 100%. Per cent data should always be regarded in the given connection.

Examples

Synthesis of inventive compounds [00113] The compound according to the present invention are synthesized from the stoichiometric amounts within 10 % deviation of the corresponding oxides and/or carbonates and/or halides of the metals in the general formula. Also high purity metals and their combinations might be used such as, but not limited to, for example metallic Si.

-25 [00114] The compound according to the present invention is prepared by one of the methods selected from the group consisting of solid state reaction methods with or without flux selected from the group consisting of B₂O₃, Bi₂O₃, l_i₂O, H3BO3, K2CO3, LiCOs, LiHCOs, Na₂CO₃, AIF₃-3H₂O, BaF₂, NH₄F, NH4CI, YF₃, K3PO4, (ΝΗ₄)₂ΗΡΟ₄, Li₂SO₄H₂O, LaNH₄(SO₄)_2l (NH₄)2SO₄, and mixtures thereof, sol-gel methods, combustion methods, precipitation methods and combinations thereof.

[00115] The mixture of starting materials is homogenized. Depending on the selected starting materials, the synthesis may consist of pre-calcination or different pre-calcination steps at 100 to 1350°C for 1 to 3 h in air and/or nitrogen and/or argon and/or vacuum and/or CO and synthesis at 1200 to 1500°C for 5 to 48 h in air or vacuum or CO or argon.

Methods used [00116] For X-ray powder diffraction (XRD) the material in powder form is exposed to X-rays of well-defined wavelength/energy (here Ka of a copper lamp was used with λ=1.5404 A obtained via filtering of white spectrum by the use of a Ni filter). The XRD was powered by 40 kV with a current of 15 mA. The XRD measurements were recorded in reflection mode.

[00117] Emission spectra were recorded using an Edinburgh Instruments Ltd. fluorescence spectrometer equipped with a mirror optic for powder samples. The excitation source used was an Osram 450 WXe discharge lamp.

[00118] Quantum efficiency (QE) was obtained from measurements of absolute photons emitted by the material over the number of photons absorbed via the use of a white standard (BaSO₄). Band gaps (E_g) were determined experimentally via data obtained from the reflection spectra of the respective undoped materials. Emission lifetimes (t) were recorded experimentally under a pulsed Xe lamp excitation and number was determined via mathematical fitting which is the well-recognized procedure. Light yield (LY) was determined mathematically according to the wellknown and accepted literature procedure using the experimental values as described above.

-26 Synthesis Example 1 [00119] Synthesis of La₂.7Euo.3Ga₅SnOi4

Starting materials: 39.50 g l_a₂O3, 41.71 Ga₂O₃, 4.70 g Eu₂O₃, 13.41 g SnO₂, and 6.0 g NH₄F. The starting materials are mixed, homogenized and fired at 150°C for 3h in air atmosphere. After the pre-calcination the composition was fired at 1250°C for 30h. The material is ground into a fine powder, washed in water, dried and sieved to narrow the particle size range. A typical XRD pattern for La₃Ga₅SnOi4:Eu³⁺ langasites is shown in Figure 1.

Synthesis Example 2 [00120] Synthesis of La2.4Euo.6Ga5Sno.9Sio.1O14

Starting materials: 35.34 g La₂O₃, 42.36 g Ga₂O₃, 9.54 g Eu₂O₃, 12.26 g SnO₂, and 0.54 g SiO₂. The starting materials are homogenized and fired at 1500°C for 10 h. The material is ground into a fine powder, washed in water, dried and sieved to narrow the particle size range.

Synthesis Examples 3 to 12 [00121] Synthesis Examples 3 to 12 were prepared in an analogous manner to the procedures as described above. For Synthesis Example 3 metallic Ge was used as a Ge source. For Synthesis Example 4 ZrO₂ was used as a Zr source. For Synthesis Example 5 HfO₂ was used as a Hf source. For Synthesis Example 6 TiO₂ and GeO₂ were used as Ti and Ge sources, respectively. Corresponding metal sources were also used for the preparation of Synthesis Examples 7 to 12.

Further Synthesis Examples [00122] In addition, the following compounds were prepared in an analogous manner to the procedures as described above: La₂.4Euo.6Ga₅SnOi4; La₃Ga5SnOi4:Eu³ (20%); La3Ga5SnOi4:Eu³ (10%); La3Ga₅SnOi4:Eu³ (2%); La^EuogGasSnogHfo iO^;

La3Ga5Tio.5Sno.5O14:Eu³ (20%); and LasGasHfo sSno sO^Eu³ (20%).

Comparative Synthesis Examples 1 to 4 [00123] Comparative Synthesis Examples 1 to 4 were prepared according to the synthesis procedure shown in WO 2009/134507 A2.

-27 [00124] Quantum efficiencies and emission peak wavelengths for different compositions of the prepared langasite compounds are shown in Table 1.

Preparation of LED [00125] General instructions for the manufacturing and measurement of phosphor-converted-LEDs (pc-LEDs): The phosphor material and an optically transparent silicone are mixed by means of a planetary centrifugal mixer to obtain a silicone-phosphor slurry. The slurry is then dispensed onto a blue or near-UV or UV- or violet-light-emitting LED-die by means of an automated dispensing equipment and cured under elevated temperatures, depending on the properties of the used transparent silicone.

[00126] The dies are driven at an operating current of 350 mA and the resultant spectra of the pc- LEDs are measured by means of a spectrometer from Instrument Systems, type CAS 140 CT combined with an integration sphere ISP 250.

Sample	Composition	QE [%]	Aem.max. [nm]
Synthesis Example 1	La2.7Euo.3Ga5SnOi4	68	612
Synthesis Example 2	La2.4EUo.6Ga5Sno.9Sio.lOl 4	80	612
Synthesis Example 3	La2.4EU0.6Ga5Sn0.9Ge0.1O14	85	612
Synthesis Example 4	La2.4EUo.6Ga5Sno.lZro.9O14	73	612
Synthesis Example 5	La2.4EUo.6Ga5Sno.9Hfo.lO14	75	612
Synthesis Example 6	La2.4EU0.6Ga5Sn0.05Ti0.05Ge0.9O14	77	619
Comparative Synthesis Example 1	La2.85Euo.o75Cro.o75Ga5SiOi4	0.2	-
Comparative Synthesis Example 2	La2.9989EUo.OOlCro.OOOlGa5SiOl4	3	-
Comparative Synthesis Example 3	La2.9249EUo.075Cro.OOOlGa5SiOl4	0.5	-
Comparative Syntehsis Example 4	La2.924EUoooiCro.075Ga5SiOl4	5	-

Table 1: Quantum efficiencies (QE) and emission peak wavelengths (Aem max.) for different compositions of langasite compounds.

[00127] Relevant data for scintillation (E_g, QE and t) and potential light yield (LY) are shown in Table 2 for different La₃Ga5(Sn,M)Oi4:Eu (20%) compounds.

Sample	M	Eg (eV)	QE (%)	j T (ms)	LY (ph/MeV)	BGOLY (ph/MeV)
Synthesis Example 7	-	4.46	68	1.1	66,290	i
Synthesis Example 8	Sir)	4.51	80	1.1	77,120	i
Synthesis Example 9	Ger)	4.54	85	1.1	81,400	8,200
Synthesis Example 10	Tir)	4.07	86	1.1	91,870
Synthesis Example 11	Zrr)	4.32	73	1.1	73,470
Synthesis Example 12	Hf’	4.43	75	1.1	73,600

Table 2: Band gap (E_g), quantum efficiency (QE), emission lifetime (t) and calculated maximum light yield (LY) for different langasite compounds and light yield of Bi₄Ge₃0i2 (BGO LY). ^r)The stoichiometric amount of M is M₀.₉g.

Claims (16)

1. Compound of the general formula (1), (LSl-a-bEUaMb^GQs-ciAciSn-i-gDgO-iq (1) where the following applies to the symbols and indices:

M is selected from the group consisting of Gd, Lu, Y, Bi, Sc, and combinations thereof;

A is selected from the group consisting of Al, Sc, In, and combinations thereof;

D is selected from the group consisting of Si, Ge, Ti, Zr, Hf, GagEg, and combinations thereof, wherein E = Nb, Ta or a combination thereof, and g = (1 -e) 0.5; and

0 < a < 0.5; 0 < b < 0.25; 0 < d < 2; and 0 < e < 1.

2. Compound according to claim 1, wherein D is Ge.

3. Compound according to claim 1 or 2, wherein 0 < a < 0.4, preferably 0 < a < 0.3, and more preferably 0 < a < 0.2.

4.

Compound according to one or more of claims 1 to 3, wherein b = 0.

5. Compound according to one or more of claims 1 to 4, wherein d = 0.

6. Compound according to one or more of claims 1 to 5, wherein 0 < e < 0.5, preferably 0 < e < 0.3, more preferably 0 < e < 0.1, and most preferably 0 < e < 0.02.

7. Compound according to Claim 1, characterised in that the following applies to the symbols and indices:

D is Ge;

0 < a < 0.4, preferably 0 < a < 0.3, more preferably 0 < a < 0.2;

b = 0;

d = 0;and

0 < e < 0.3, preferably 0 < e < 0.1, more preferably 0 < e < 0.02.

8. Compound according to one or more of Claims 1 to 7, characterised in that the compound is coated on the surface with another compound.

9. Process for the preparation of a compound according to one or more of Claims 1 to 8, comprising the steps:

a) preparation of a composition comprising starting materials of the respective metals contained in the compound of general formula (1), wherein the starting materials are independently selected from pure metal elements, metal oxides, metal carbonates, metal halides and mixtures thereof; and

b) calcination of the composition.

10. Blend comprising a compound according to one or more of claims 1 to

8 and at least one further luminescent material.

11. Blend according to claim 10, wherein the at least one further luminescent material is selected from phosphor materials or quantum materials.

12. Light source comprising the compound according to one or more of claims 1 to 8 or the blend according to claim 10 or 11 as light-emitting material.

13. Light source according to claim 12, wherein the light source is a fluorescent lamp, wherein the light-emitting material is excited by a gas discharge.

14. Light source according to claim 12, wherein the light source is an LED comprising at least one primary light source emitting UV, violet and/or

- 32 blue light, wherein the light-emitting material converts the light of the primary light source into light having a longer wavelength.

15. Use of the compound according to one or more of claims 1 to 8 as scintillation material in medical imaging detectors or detectors for high energy radiation.

16. Use of the compound according to one or more of claims 1 to 8 as persistent luminescent material for security applications, medical imaging or temperature sensing.