JP2023123882A - Light-emitting material, light-emitting ink, light-emitting body, and light-emitting device - Google Patents

Abstract

To provide a novel light-emitting material that contains a rare earth complex fixed on a substrate and has high emission quantum efficiency.SOLUTION: Disclosed is a light-emitting material including: a substrate that includes a metal oxide and/or a metal sulfide; two or more linker groups bonded to the substrate; a phosphine oxide ligand bonded to each of the linker groups, each phosphine oxide ligand having one phosphine oxide group; and a rare earth ion. A rare earth complex is formed by one rare earth ion and two or more phosphine oxide ligands.SELECTED DRAWING: Figure 6

Description

The present invention relates to luminescent materials, luminescent inks, emitters and luminescent devices.

Attempts have been made to immobilize a luminescent rare earth complex on a substrate containing silica or the like (for example, Patent Document 1, Non-Patent Document 1).

Patent Document 1 discloses a method of obtaining a phosphor by adding an aqueous solution of aluminum nitrate and an aqueous solution of europium nitrate to porous silica, mixing the mixture, drying and firing the mixture, and surface-treating the fired product with a silane coupling agent. do. Although aluminum and europium are fixed on silica, it is not clear in what form it is and it is thought that they adhere unevenly.

Non-Patent Documents 1 and 2 disclose europium complex-containing particles in which bidentate ligands such as phosphine oxide ligands or bipyridine ligands are bound to silica via one linker group.

WO2018/037914

Biju Fracis et al., Eur. J. Inorg. Chem, 2017, 3205-3213 Langmuir, 2013, 29, 5878-5888

Conventional luminescent materials comprising rare earth complexes immobilized on substrates tended to exhibit lower luminous quantum efficiencies compared to unimmobilized rare earth complexes. Accordingly, one aspect of the present invention provides a novel luminescent material that includes a rare earth complex immobilized on a substrate and exhibits high luminous quantum efficiency.

One aspect of the invention is a substrate comprising at least one of a metal oxide or metal sulfide, two or more linker groups attached to the substrate, and one phosphine oxide attached to each of the linker groups. A luminescent material is provided that includes a phosphine oxide ligand having a group and a rare earth ion. A rare earth complex is formed by one of the rare earth ions and two or more of the phosphine oxide ligands.

Another aspect of the present invention provides a luminescent ink containing the luminescent material and a dispersion medium in which the luminescent material is dispersed.

Yet another aspect of the present invention provides a light emitter containing the light emitting material, and a light emitting device comprising the light emitter.

According to one aspect of the invention, novel luminescent materials are provided that include a rare earth complex immobilized on a substrate and exhibit high luminous quantum efficiency.

1 is a transmission electron micrograph of silica nanoparticles. 1 is a transmission electron micrograph of a luminescent material containing silica nanoparticles and rare earth complexes. 2 is an EDS spectrum of a luminescent material containing silica nanoparticles and rare earth complexes; FT-IR spectra of luminescent materials or rare earth complexes. Excitation spectra of ligands, rare earth complexes or luminescent materials. 1 is an emission spectrum of a luminescent material or a rare earth complex; 4 is a graph showing luminescence attenuation of luminescent materials or rare earth complexes.

Several embodiments of the invention are described in detail below. However, the present invention is not limited to the following embodiments.

A luminescent material according to one embodiment comprises a substrate comprising at least one of a metal oxide or a metal sulfide, two or more linker groups bonded to the substrate, and one phosphine oxide bonded to the linker group. A plurality of phosphine oxide ligands having groups and a plurality of rare earth ions. A rare earth complex is formed by one rare earth ion and two or more phosphine oxide ligands.

The following chemical formula (I) schematically shows an example of the luminescent material.

In formula (I), X represents a substrate, L represents a linker group attached to the substrate X and the phosphine oxide ligand ((Ar ¹ )Ar ² )P=O), Ln(III) represents a rare earth indicates an ion. Ar ¹ and Ar ² each independently represent an optionally substituted aryl group. Z represents an n-dentate ligand forming a coordination bond with the rare earth ion M(III). In formula (I), one rare earth ion M(III), two phosphine oxide ligands, and 6/n ligands Z form a rare earth complex. The number of phosphine oxide groups bonded to one linker group L is typically one. Although only one rare earth complex is illustrated in formula (I), typically multiple rare earth complexes are attached to the substrate X via linker groups L. According to the findings of the present inventors, by immobilizing the rare earth complex on the substrate X via two or more linker groups, the rare earth complex is stably immobilized on the substrate X, and the substrate It is believed that light emission with a higher quantum yield can be achieved compared to unfixed rare earth complexes.

The shape of the base material X is not particularly limited, and for example, the base material X may be a particle, film or plate. When the base material X is particles, the luminescent material into which the rare earth complex is introduced is usually also particulate. Particulate luminescent materials are expected to be applied, for example, as luminescent ink or fluorescent particles used in the biomedical field. A film as a substrate may be, for example, a plastic film. A plate-like body as a substrate may be, for example, a glass plate.

When the substrate X is particles, the average particle size may be 1000 nm or less, 500 nm or less, 100 nm or less, or 10 nm or more. A particulate luminescent material having nanoparticles having a nano-order particle size as a base material X tends to have good dispersibility in various dispersion media. The particle diameter of the luminescent material into which the rare earth complex is introduced may be 1000 nm or less, 500 nm or less, 100 nm or less, or 10 nm or more.

Substrate X includes metal oxides, metal sulfides, or both. Examples of metal oxides include silicon dioxide (silica), zinc oxide, calcium oxide, titanium oxide, aluminum oxide, and indium tin oxide (ITO). Examples of metal sulfides include zinc sulfide and cadmium sulfide. The base material X may be a glass body (for example, silica glass, ITO glass, fluorine glass) or a crystal. The total content of metal oxides and metal sulfides in the substrate X is 50 to 100% by mass, 60 to 100% by mass, 70 to 100% by mass, 80 to 100% by mass, based on the mass of the substrate X, Or it may be 90 to 100% by mass.

The linker group L has a functional group forming a bond with the metal oxide or metal sulfide of the substrate X. Functional groups can be, for example, residues of hydrolyzable silyl groups. The linker group L may further have an arylene group bound to the phosphine oxide group. The linker group containing a residue of a hydrolyzable silyl group and an arylene group may be, for example, a moiety other than X among groups represented by the following formula (1).

In formula (1), X represents a base material, R ¹ represents a divalent organic group, R ² represents an alkyl group having 1 to 5 carbon atoms or 1 to 3 carbon atoms, and Ar ³ represents a phosphine oxide group and Indicates a bonded arylene group (eg, phenylene, biphenylene, naphthylene). p is an integer of 1 to 3 corresponding to the number of atoms bonded to the substrate X among the three oxygen atoms bonded to Si. * indicates the portion of the phosphine oxide group that is bonded to the phosphorus atom. R ¹ is typically an organic group derived from a synthetic route deriving a linker group. For example, R ¹ may be a group containing an amide group, and an example of the linker group L in that case is represented by the following formula (1a). R ³ in formula (1a) represents an alkylene group. The number of carbon atoms in the alkylene group as R ³ may be, for example, 1 or more or 2 or more, and may be 20 or less, 15 or less, or 10 or less.

Ar ¹ and Ar ² in formula (I) each independently represent an optionally substituted aryl group. An aryl group as Ar ¹ or Ar ² can be the residue of an aromatic compound with one hydrogen atom removed. Specific examples of aryl groups include substituted or unsubstituted benzene, substituted or unsubstituted naphthalene, substituted or unsubstituted anthracene, or substituted or unsubstituted phenanthrene with one hydrogen atom removed. . In particular, Ar ¹ and Ar ² may be substituted or unsubstituted phenyl groups. A halogen atom may be sufficient as the substituent which an aryl group has.

The rare earth ions that constitute the rare earth complex introduced into the light-emitting material are usually trivalent rare earth ions. Rare earth ions can be appropriately selected according to the emission color and the like. Rare earth ions are, for example, Eu(III) ions, Tb(III) ions, Gd(III) ions, Sm(III) ions, Yb(III) ions, Nd(III) ions, Er(III) ions, Y ( It can be at least one selected from the group consisting of III) ions, Dy(III) ions, Ce(III) ions, and Pr(III) ions. From the viewpoint of obtaining high emission intensity, the rare earth ions may be Eu(III) ions, Tb(III) ions or Gd(III) ions.

The luminescent material exemplified as formula (I) further has an n-dentate ligand Z other than the phosphine oxide ligand with the linker group L, forming a coordinate bond with the rare earth complex. The ligand Z may be a bidentate ligand, examples of which include diketone ligands represented by the following formula (2). The diketone ligand can contribute to further improvement of the emission intensity of the rare earth complex through its photosensitizing action.

In formula (2), R ¹¹ and R ¹² each independently represent an optionally substituted aliphatic group or an optionally substituted aromatic group, R ¹³ is a hydrogen atom, represents an optionally substituted aliphatic group or an optionally substituted aromatic group, wherein R ¹³ optionally has a substituent by bonding to R ¹¹ or R ¹² A cyclic group may be formed. R ¹³ may be a deuterium atom.

R ¹¹ , R ¹² and R ¹³ may each independently be an alkyl group (eg, methyl group, tert-butyl group), halogenated alkyl group, aryl group or halogenated aryl group. The alkyl group and the halogenated alkyl group may have 1 to 10 carbon atoms. The halogenated alkyl group as R ¹¹ , R ¹² or R ¹³ is a fluoroalkyl group having 1 to 5 carbon atoms (eg, trifluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group). The aryl group as R ¹¹ , R ¹² or R ¹³ may be a phenyl group, naphthyl group or thienyl group, which may be halogenated.

The cyclic group formed by combining R ¹³ with R ¹¹ or R ¹² may be an optionally substituted cyclic aliphatic group, an aromatic group, or a group consisting of a combination thereof.

The ligand Z may have optical activity. By introducing an optically active ligand Z into a light-emitting material, the light-emitting material can be endowed with circularly polarized light properties. The optically active ligand Z may be, for example, a camphor derivative represented by the following formula (20) or an enantiomer thereof. Any ratio of the two enantiomers may be combined.

In formula (20), R ²¹ has the same definition as R ¹¹ in formula (2). R ²² , R ²³ and R ²⁴ each independently represent an optionally substituted hydrocarbon group, R ²⁵ , R ²⁶ , R ²⁷ and R ²⁸ each independently represent a hydrogen atom, a halogen atom, or a substituted indicates a hydrocarbon group which may have a group. R ²¹ , R ²² and R ²³ may be optionally substituted alkyl groups and may have 1 to 5 carbon atoms. A specific example of R ²¹ , R ²² and R ²³ is a methyl group. R ²⁴ , R ²⁵ , R ²⁶ and R ²⁷ may each independently be an optionally substituted alkyl group and may have 1 to 5 carbon atoms. R ²⁴ , R ²⁵ , R ²⁶ and R ²⁷ may be hydrogen atoms. Specific examples of camphor derivatives represented by formula (20) and enantiomers thereof include 3-(trifluoroacetyl)camphorate and 3-(perfluorobutyryl)-(±)-camphorate.

The luminescent material includes, for example, a linker group containing a functional group (for example, a hydrolyzable silyl group) that forms a bond with the metal oxide or metal sulfide of the substrate X, and a phosphine oxide ligand containing a phosphine oxide group. A compound having the compound can be obtained by a method comprising the steps of: bonding to a substrate X; and forming a rare earth complex with a phosphine oxide ligand bonded to the substrate X via a linker group and a rare earth ion. Formula (3) below shows an example of a compound having a linker group containing a hydrolyzable silyl group and a phosphine oxide ligand, which can be used in the production of a luminescent material. R ¹ , R ² , Ar ¹ , Ar ² and Ar ³ in formula (3) are as defined above.

The compound of formula (3) is, for example, a compound having a hydrolyzable silyl group and an amino group represented by formula (11) below, and a phosphine oxide group and a carboxyl group represented by formula (12) below. It can be obtained by reaction with a compound having or a derivative thereof. Any compound containing a combination of functional groups capable of forming a chemical bond by reaction can be arbitrarily applied without being limited to the reaction of amino groups and carboxyl groups as in formulas (11) and (12).

A luminescent ink according to one embodiment may include a particulate luminescent material and a dispersion medium in which the luminescent material is dispersed. A luminescent film can be formed by a printing method or the like using luminescent ink. The dispersion medium is not particularly limited, and may be, for example, methanol, ethanol, water, acetone, hexane, chloroform, dichloromethane, diethyl ether, ethyl acetate, benzene, toluene, or combinations thereof. Luminescent inks may include styrene, acrylic acid, methacrylic acid, acrylic acid derivatives, methacrylic acid derivatives (methyl methacrylate, ethyl methacrylate, etc.), or polymers (polystyrene, polymethyl methacrylate, etc.).

A light emitter according to this embodiment includes the light emitting material according to the above-described embodiments. This light emitter can constitute various light emitting devices or security materials. Examples of light emitting devices include micro LEDs, displays such as traffic signs and illuminated signs, liquid crystal backlights, and illuminated displays.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples. However, the present invention is not limited to these examples.

1. Synthesis (1) Eu(hfa) ₃ ( _H2O ) ₂
10 mL of europium acetate monohydrate (0.87 g, 2 mmol) was dissolved in distilled water. A solution of 1,1,1,5,5,5-Hexafluoro-2,4-pentandinone (0.9 mL, 6 mmol) was added dropwise thereto. After stirring at room temperature for 4 hours, the precipitated yellow powder was separated by filtration and recrystallized from a mixed solvent of methanol/water. The resulting crystals were washed with toluene and dried under vacuum to give Eu(hfa) ₃ (H ₂ O) ₂ (1.12 g, 69% yield).
IR spectrum (cm ^-1 ): ν(C=O) 1647 (s), ν(CF) 1251-1136 (s)cm ^-1
1 H NMR (CD ₃ OD, 400 MHz, 300K) δ, ppm: 3.90 (s, 3H, CF ₃ CH); ¹⁹ F NMR (CD ₃ OD, 376 MHz, 300 K) δ, ppm: -80.8 (s , _CF3 ) ppm

(2) Synthesis of 4-(diphenylphosphino)benzoic acid

Diphenyl(p-tolyl)phosphine (5.0 g) was placed in a Schlenk tube followed by KMnO ₄ (11.1 g) and NaOH (0.43 M, 65 mL). The Schlenk tube was heated at 90° C. for 15 hours and the hot suspension was filtered through celite. The resulting solution was washed twice with diethyl ether and 50% H ₂ SO ₄ was added to precipitate solids. Solids were filtered off and recrystallized from ethanol. The collected white crystals were washed with diethyl ether and dried under vacuum to obtain 4-(diphenylphosphino)benzoic acid (3.1 g, 55% yield).
IR spectrum (cm ^-1 ): ν(COO) 1705(s) and 1251(s), ν(P=O)1155(s)
¹ H NMR (CD ₃ OD, 400 MHz, 300K) δ (ppm): 8.16 (m, 2H, Ar); 7.76 (m, 2H, Ar); 7.67 (m, 6H, Ar); 7.58 (m, 4H ,Ar). ³¹ P NMR (CD ₃ OD, 162 MHz, 300K) δ (ppm) : 32.1 (s)

(3) Phosphine oxide ligand TPPO-Si(OEt) ₃

4-(Diphenylphosphino)benzoic acid (0.61 g, 1.95 mmol) was placed in a Schlenk tube and thionyl chloride (12 mL) was added under a nitrogen atmosphere. After 2 hours of reaction at room temperature, excess thionyl chloride was removed to give a pale yellow solid. This solid was dissolved in dry acetotrile (10 mL), triethylamine (2.16 mL, 15.34 mmol) and 3-aminopropyltriethoxysilane (0.49 mL, 2.05 mmol) were added to the solution and the solution was stirred at room temperature for 1.5 hours. did. Solvent was removed and the solid was suspended in water and extracted with methylene chloride. The methylene chloride layer was washed with saturated brine, dried over magnesium sulfate, and the solvent was removed to give a dark brown crude product. The crude product was purified by silica gel column chromatography using ethyl acetate as eluent to give TPPO-Si(OEt) ₃ (577 mg, 56% yield).
Elemental analysis calcd for _C28H36NO5PSi ( _525.66 ): C, 63.98; H, 6.90 _; N, 2.66; Found: C, 63.64; H, 6.97;
¹ H NMR (CD ₃ OD, 400 MHz, 300K) δ (ppm): 7.94 (m, 2H, Ar), 7.54-7.78 (m, 12H, Ar) overlapping with (t, 1H, CO-NH), 3.83 (t, 6H, CH2 _- O-Si), 3.38 (m, _2H , N _{- CH2CH2CH2} -Si), 1.72(t, 2H, _-CH2- CH2 _- Si), 1.20 (t , 9H, _CH3 - _CH2 -O-),0.68 (t, 2H, _-CH2 -Si)
³¹ P NMR (CDCl ₃ , 162 MHz, 300K) δ (ppm): 32.1 (s)

(4) Eu complex (Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ )

Eu(hfa) ₃ (H ₂ O) ₂ was dehydrated by heating at 135° C. for 4 hours under a vacuum of 1×10 ⁻³ mbar. Dehydrated Eu(hfa) ₃ (H ₂ O) ₂ (90 mg, 0.11 mmol) was placed in a Schlenk tube, dry ethanol (10 mL) was added under a nitrogen atmosphere, and then TPPO-Si(OEt) ₃ (115 mg. 0.22 mmol) was added. The yellow solution formed was stirred at room temperature for 5 hours. The solvent was then removed and the product was dried under vacuum to give )Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ (yield 189 mg, 94% yield).
Elemental analysis calcd (%) for _{C71H75EuF18N2O16P2Si2} ( _1824.4 ) _: C _, 46.74; H _, 4.14 _; N, 1.54; _Found : C, 46.59; H, 4.38;

(5) Silica nanoparticles Ammonia solution (28%, 9.5 mL), triethoxysilane (7.0 mL), and absolute ethanol (183 mL) were placed in a round bottom flask. The formed solution was stirred overnight at 45° C. to obtain a milky white dispersion containing silica nanoparticles. Silica nanoparticles were collected by centrifugation at 4000 rpm and dispersed in absolute ethanol (185 mL) by ultrasonic method.

(6) Luminescent material with Eu complex immobilized on silica nanoparticles ( _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ )

An ethanol dispersion of silica nanoparticles (6 mL) was placed in a round-bottomed flask, to which TPPO-Si(OEt) ₃ (142 mg, 0.270 mmol) was slowly added under a nitrogen atmosphere, and the mixture was stirred overnight at room temperature. . Then dehydrated Eu(hfa) ₃ (H ₂ O) ₂ (109 mg, 0.135 mmol) was added and the resulting reaction was stirred at room temperature for 12 hours. Silica nanoparticles were isolated by centrifugation and washed with diethyl ether until no red effluent was observed under UV light (365 nm). The washed particles were dried under vacuum to obtain pale yellow silica nanoparticles (SiO ₂ -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ ) modified with Eu complexes.

2. Evaluation (1) Particle size Silica nanoparticles before modification with an Eu complex and a luminescent material ( _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ ) which is silica nanoparticles modified with an Eu complex. Measured by dynamic light scattering method. The average particle size of the silica nanoparticles before modification was 36 nm, and the average particle size of the particulate luminescent material ( _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ ) was 53 nm.

(2) Transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDS)
Silica nanoparticles before modification and silica nanoparticles modified with an Eu complex (SiO ₂ -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ ) were observed with a transmission electron microscope. Figure 1 is a transmission electron micrograph of silica nanoparticles before modification, and Figure 2 is a transmission electron micrograph of particulate luminescent material ( _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ ). It is a photomicrograph. In the image of SiO ₂ -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ , many dark regions thought to be derived from Eu complexes were observed. Furthermore, when an image of _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ was analyzed by energy dispersive X-ray spectroscopy (EDS), the presence of Eu, P, F, Si, C and O was confirmed, which also suggested that the Eu complex was introduced onto the silica nanoparticles. FIG. 3 is an EDS spectrum of _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ .

(3) Fourier transform infrared spectroscopy (FT-IR)
_{FIG . 4 shows the FT- _ _} IR spectrum. In the FT-IR spectra of Eu(hfa) ₃ (TPPO) ₂ and Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ , the P=O stretching observed in the case of TPPO-Si(OEt) ₃ No derived signal at 1184 cm ⁻¹ was observed and a signal at 1142 cm ⁻¹ was observed, such a signal shift suggesting the formation of a coordinate bond between the P═O group and Eu(III).

(4) Thermogravimetric Analysis By thermogravimetric analysis, the decomposition temperatures of Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ and _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ were respectively 208°C and 306°C were confirmed.

_{( 5 ) Photophysical Properties _ _ 3} Excitation spectrum of [TPPO-Si(O) ₃ ] ₂ . Excitation spectra ^of Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ and SiO ₂ -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ show A broad absorption due to

FIG. 6 shows solid-state Eu(hfa) ₃ ( _H2O ) ₂ , Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ , and _SiO2 -Eu(hfa) ₃ [TPPO-Si(O). ) ₃ ] ₂ emission spectrum (excitation light: 356 nm). _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ was compared with Eu(hfa) ₃ ( _H2O ) ₂ and Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ . and showed remarkably strong luminescence.

FIG. 7 shows solid-state Eu(hfa) ₃ ( _H2O ) ₂ , Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ , and _SiO2 -Eu(hfa) ₃ [TPPO-Si(O). ) ₃ ] ₂ and Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ in solution. _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ was compared with Eu(hfa) ₃ ( _H2O ) ₂ and Eu(hfa) ₃ [TPPO-Si(OEt) ₃ ] ₂ . and exhibited a long emission lifetime. Table 1 shows the photophysical properties of each Eu complex (luminescence lifetime τ _obs , radiative rate constant k _r , non-radiative rate constant k _nr , 4f-4f transition luminescence quantum efficiency Φ _ff and total luminescence quantum yield Φ _tot ). _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ showed a relatively large kr and a small knr. _SiO2 -Eu(hfa) ₃ [TPPO-Si(O) ₃ ] ₂ is prepared by immobilizing the rare earth complex on the substrate X using two or more linker groups. It is thought that the stable immobilization enables an increase in radiation velocity and suppression of the thermal deactivation process, resulting in high luminescence quantum efficiency.

Claims (9)

a substrate comprising at least one of a metal oxide or a metal sulfide;
two or more linker groups attached to the substrate;
a phosphine oxide ligand having one phosphine oxide group attached to each said linker group;
rare earth ions;
including
a rare earth complex is formed by one of the rare earth ions and two or more of the phosphine oxide ligands;
Luminescent material. 2. The luminescent material of claim 1, wherein the linker group comprises residues of hydrolyzable silyl groups and arylene groups. 3. A luminescent material according to claim 1 or 2, wherein the substrate comprises silicon dioxide. The luminescent material according to any one of claims 1 to 3, further comprising an optically active ligand forming a coordinate bond with the rare earth ion. A luminescent material according to any one of claims 1 to 4, wherein the substrate is a particle. The luminescent material according to any one of claims 1 to 4, wherein the substrate is particles having an average particle size of 100 nm or less. A luminescent ink comprising the luminescent material according to claim 5 or 6 and a dispersion medium in which the luminescent material is dispersed. An emitter comprising the luminescent material according to any one of claims 1-6. A light emitting device comprising the light emitter according to claim 8 .