JPS649356B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a main lattice (host) consisting of a crystalline inorganic compound containing lanthanum as one of the main components.
lattice), activated by gadolinium, and further containing a second activator element and a third activator element. Already published Dutch patent application no.
No. 7607724 contains gadolinium, is activated by terbium and/or dysprosium in addition to bismuth, and has the formula: La _1-xyz Gd _x Bi _y A _z
B ₃ O ₆ (A in the formula represents terbium and/or dysprosium, 0x1, 0.001y
0.80, 0z0.60 and x+y+z1). In this borate, gadolinium is a constituent of the main lattice, and the activator element bismuth is excited by ultraviolet radiation from a low-pressure mercury vapor discharge lamp consisting primarily of a wavelength of about 254 nm, and this excitation energy is then transferred to the activator element. Transitioning from bismuth to activator element A, and depending on the activator element selected as A, exhibits the emission characteristics of terbium or dysprosium. A condition for obtaining efficient terbium or dysprosium luminescence is that the material contains gadolinium, preferably in relatively large amounts. The reason for this is unknown, but it is thought that it is because only gadolinium plays the role of the main component of the main lattice. Usually, a luminescent material has a crystalline inorganic compound as its main lattice, and a small amount of an activator element is usually mixed therein. The main lattice group, which is important for luminescent materials, is formed by compounds containing as one of the main components an element selected from the group consisting of yttrium, lanthanum and lanthanides. Such a main lattice is represented by a rare earth lattice and can contain, in addition to the above-mentioned cations such as Y, La and lanthanides, other cations such as alkali metals and alkaline earth metals as a main component. Gadolinium-activated luminescent materials have been known for a long time (e.g., F.A. Kroger: Some Aspects of
The Luminous Sense of Solid
Aspects cf the Luminescence cf Solids)
(1948), p. 293). Gd-activated rare earth lattices, especially Gd-activated yttrium tantalate, are known as the ``Journal of Luminescence''.
Luminescence) 3 (1970), page 109. A generally known phenomenon that can be used advantageously in luminescent materials is the transfer of excitation energy from one type of activator element (the so-called sensitizer) to another type of activator element (the actual activator). It is. Such transition may be complete;
It may also be only a part of it. In the former case, only the activator's luminescence is observed, and in the latter case, the sensitizer's luminescence is observed in addition to the activator's luminescence. In many cases, the condition for energy transfer to occur is that the sensitizer emits light in the portion of the spectrum in which the activator can be excited. It is known that the transfer of excitation energy to gadolinium can occur in luminescent materials. "Appl. Phys. Lett." 21 (1972) p. 57 lists, for example, thallium-activated glasses and gadolinium-activated glasses. In such materials, the exciting radiation is absorbed by thallium, which acts as a sensitizer, and transferred to gadolinium. Furthermore, it is known that gadolinium can act as a sensitizer. “Structure and Bonding”
Bonding), 13 (1973), p. 53, describes the energy transfer from gadolinium to terbium in luminescent materials. German Patent Specification No.
No. 1284296 discloses gadolinium-activated and terbinium-activated boric acid alkaline earth metal alkali metal salts. A significant drawback of many luminescent materials containing sensitizers and activators is that in order to achieve complete energy transfer to the activator and obtain the maximum possible emission of the desired activator radiation, very high activators are required. Concentration is often required. However, normally at such high activator concentrations so-called concentration quenching occurs, resulting in very low luminous fluxes. It is therefore necessary to use small amounts of activator, in which case the energy transfer is not optimal. Materials that do not exhibit concentration quenching even at high activator concentrations often have the disadvantage of being extremely expensive. The reason for this is that expensive rare earth metals are usually used as activators. The object of the invention is to obtain a gadolinium-activated material in which a transfer of excitation energy can occur and whose emission is desired to reduce the concentration of activator. The luminescent material of the present invention is a borate represented by the following formula: La _x Gd _1-xyz Bi _y Mn _z B ₃ O ₆ (0x0.5 0.001y0.1 0.001z0.2). Such borates exhibit efficient Mn emission in the green portion of the spectrum when excited by short wavelength ultraviolet radiation. The present invention provides efficient transfer of excitation energy from the second activator element to the third activator element via gadolinium in a rare earth metal lattice containing gadolinium, a second activator element, and a third activator element. This is based on the fact that we have confirmed that it can be made to occur. In principle, this mechanism can occur in all crystalline rare earth metal lattices that have been activated as described above. but,
When a photosensitive material activated by Gd and a second activator element only (i.e. in the absence of a third activator element) is excited by short wavelength ultraviolet radiation, The condition is that it exhibits the characteristic line luminescence of Gd, and in some cases, exhibits the luminescence characteristic of the second activator element. The ultraviolet radiation used in such tests to determine whether a rare earth lattice containing Gd is suitable for activation by a certain combination of second and third activator elements consists primarily of low pressure wavelengths of approximately 254 nm. This is the mercury resonance radiation of mercury vapor discharge. From the above description, it can be seen that in the luminescent material of the present invention, energy transfer occurs in two stages: transfer from the second activator to Gd and transfer from Gd to the third activator. In this process,
Because mutual transfer between Gd ions can occur, this tertiary activator is usually
Complete transfer to the active agent can be achieved. An important advantage of the luminescent material of the present invention is that it can exhibit efficient light emission from the third activator element even at low third activator concentrations. Therefore, the risk of concentration quenching is reduced and a high luminous flux can be achieved. Additionally, lower third activator concentrations usually result in less expensive materials. The numerical limitations in the above general formula mean the range in which the luminescent material exhibits desired luminescence. As mentioned above, the luminescent material of the present invention is a borate that emits manganese radiation;
Contains seed activator elements, namely Gd, Bi and Mn. The second activator element Bi is excited by 254 nm radiation from a low-pressure mercury vapor discharge lamp, and this excitation energy is transferred to the third activator element Mn through the activator element Gd.
, and then Mn emits in the green part of the spectrum. If Gd does not exist,
The energy transfer from Bi to Mn is extremely small. In the luminescent material of the present invention, since the presence of Gd is essential for energy transfer, Gd is not a constituent of the main lattice of borate but is an activator element. Further, since the luminescent material of the present invention is activated with divalent Mn, it emits light in one narrow band having a maximum value at 520 nm. This type of luminescence has been demonstrated in various practical applications compared to the spectrum of terbium consisting of many lines or the spectrum of dysprosium consisting of two bands in luminescent materials as shown in the aforementioned Dutch patent application No. 7607724. This is highly desirable in many applications. The luminescent material of the invention can be used in luminescent screens, preferably luminescent screens of low-pressure mercury vapor discharge lamps. The luminescent material of the present invention is, for example,
It can be advantageously used in the following applications: (1) as a green-emitting component in multicomponent low-pressure mercury vapor discharge lamps for general lighting, in combination with a blue-emitting component and a red-emitting component; (2) for photochemical processes. (3) in low-pressure mercury vapor discharge lamps for irradiating infants with hyperbilirubinemia, and (4) for irradiating plants to study plant growth. in low-pressure mercury vapor discharge lamps. In such discharge lamps, it is often desired to emit light from one or more of the above-mentioned third activator elements, both for general lighting and for special uses. The luminescent material of the present invention can be produced by a conventional method for producing luminescent materials. It is common practice to subject the starting mixtures of the elements that make up the compound to a solid state reaction at elevated temperatures. Next, embodiments of the present invention will be described with reference to the drawings. Example 1 A mixture was made consisting of the following materials: Gd ₂ O ₃ 4.441 g La ₂ O ₃ 1.579 g H ₃ BO ₃ 6.813 g (5% excess) Bi ₂ O ₂ CO ₃ 0.116 g MnCO ₃ 0.044 g. The mixture was heated to 1000° C. twice for 1 hour each in a nitrogen atmosphere.
The product had the formula: La _0.277 Gd _0.7 Bi _0.013 Mn _0.01 B ₃ O ₆ and emitted in the green emission band (maximum approximately 520 nm) when excited with 254 nm radiation. The quantum yield was 55%. Figure 1 shows the spectral distribution of the emitted radiation. In FIG. 1, the wavelength λ (nm) is plotted on the horizontal axis, and the relative radiation intensity E (arbitrary unit) is plotted on the vertical axis. A small contribution of Gd emission was still observed at 310-315 nm. In Figure 1, this luminescent line is shown on a 10x scale. Examples 2 and 3 Two types of luminescent borates with different activator contents were prepared in the same manner as in Example 1. Table 1 shows the formulas expressing these substances and the measurement results of quantum rates q (%) when these substances are excited with 254 nm radiation.

[Table] Figure 2 shows a cross section of a low-pressure mercury vapor discharge lamp using the luminescent material of the present invention. This low-pressure mercury vapor discharge lamp comprises a tubular glass wall 1. 1 at each end of the discharge lamp
Electrodes 2 and 3 are installed one by one, and a discharge occurs between these electrodes during operation. The discharge lamp is charged with a rare gas mixture, which acts as a starting gas, together with a small amount of mercury. The inner surface of the wall 1 is coated with a luminescent layer 4. Luminous layer 4
contains the luminescent material of the present invention. Luminous layer 4
can be deposited in a conventional manner, for example by means of a suspension containing the luminescent material.

[Brief explanation of drawings]

FIG. 1 is a graph showing the energy spectral distribution of radiation emitted from the luminescent material of the present invention, and FIG.
The figure is a cross-sectional view of a low-pressure mercury vapor discharge lamp using the luminescent material of the present invention. 1... Glass wall, 2, 3... Electrode, 4... Photosensitive layer.

Claims (1)

[Claims] A luminescent material which is a borate expressed by the following formula: La _x Gd _1-xyz Bi _y Mn _z B ₃ O ₆ where 0x0.5 0.001y0.1 0.001z0.2.