RU2533709C2 - Monocrystalline fluorescent material for white light-emitting diodes - Google Patents

Abstract

FIELD: physics, optics.

SUBSTANCE: invention relates to fluorescent materials and specifically to a monocrystalline fluorescent material for white light-emitting diodes. The material is a solid solution of aluminium oxide and yttrium aluminium garnet with cerium and has a composition corresponding to the formula Y_3-xCe_xAl_5+yO_12+1.5y, where x=0.02-0.05, y=0.17-3.97.

EFFECT: high photoluminescence intensity of the fluorescent material coupled with high operational stability in varying climatic conditions.

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Description

The invention relates to the field of phosphors, which have the ability to luminesce when exposed to radiation from a mercury-quartz lamp (or other radiation sources) and can be used in white light emitting diodes.

The phosphors for white light-emitting diodes are widely known, the material of which is yttrium-aluminum garnet with cerium (YAG: Ce). These are epitaxial films and powders, less often - transparent ceramics ("Photoluminophors based on YAG, activated by Се ⁺³ , in white light-emitting diodes" Merkushev OM, Vedernikova LG St. Petersburg State Technological Institute). These materials, in addition to the complexity and high cost of obtaining them, work in fairly narrow temperature ranges and climatic conditions and have limitations on the service life - the luminous flux may fall by half after several thousand hours of operation.

Closest to the proposed invention are phosphors based on a fluorescent material - yttrium-aluminum garnet activated by cerium (YAG: Ce) with various compositions, including yttrium and aluminum, while maintaining the stoichiometry of yttrium-aluminum garnet (US Patent No. 5998925, IPC: H01J 1/62, H01J 63/04, 1997). However, the known phosphor material has insufficient photoluminescence intensity with limited operation in certain climatic conditions, which significantly narrows the scope of white light emitting diodes.

The technical task of the invention is to increase the intensity of the photoluminescence of the phosphor material in combination with its high stability in varying climatic conditions.

The stated technical problem is solved due to the fact that the single-crystal phosphor material for white light-emitting diodes, including yttrium - cerium activated aluminum garnet, is a solid solution of aluminum oxide and yttrium-aluminum garnet with cerium and has a composition corresponding to the formula

Y _3-x Ce _x Al _{5 + y} O _{12 + 1,5y} ,

where x = 0.02-0.05,

y = 0.17-3.97.

Distinctive features of the present invention is that the phosphor material is a solid solution of aluminum oxide and yttrium-aluminum garnet with cerium and has a composition corresponding to the formula

Y _3-x Ce _x Al _{5 + y} O _{12 + 1,5y}

where x = 0.02-0.05,

y = 0.17-3.97.

It should be noted that the main contribution to the increase in the intensity of photoluminescence is made by an increase in the content of aluminum oxide in the composition of the solid solution, and even with the same amount of cerium, the intensity of photoluminescence increases significantly.

The indicated properties of the phosphor material are related to the fact that a high concentration of aluminum oxide compared with yttrium-aluminum garnet activated by cerium promotes the formation of cerium-containing aluminum nanoclusters in the melt, which leads to an increase in the cerium concentration coefficient and the uniformity of its distribution in the crystalline matrix of the solid solution.

The optimal composition of the solid solution was determined empirically; at y = 0, the photoluminescence does not exceed 45,000 rel. units, at y> 3.99, luminescence is practically not observed, since the solid solution is close to eutectic in composition. The maximum photoluminescence intensity is observed at y = 2.9, and this composition of the solid solution should be considered optimal.

Example 1. To obtain a solid solution of composition Y _2.95 Ce _0.05 Al ₅ O ₁₂ (y = 0) a mixture of powdery oxides with a total weight of 1200 g of the composition was prepared: Y ₂ O ₃ - 674.87 g; CeO ₂ - 8.76 g; Al ₂ O ₃ - 516.47 g. After stirring, the mixture was placed in a molybdenum crucible, which was installed in a heat unit with a tungsten heater of the Sapphire 2MG industrial unit. Melting and subsequent crystallization of the mixture was carried out by directed crystallization in vacuum at a crucible pulling speed through the heating zone of 4 mm / h. After the cycle is completed, the material is removed from the crucible. It is yellow in color, transparent, does not contain extraneous phases. A photoluminescence spectrum was taken from a sample of the obtained material upon excitation by a mercury-quartz lamp. The photoluminescence intensity did not exceed 45,000 rel. units with an emission peak at a wavelength of 540 nm (Fig. 1).

Example 2. To obtain a solid solution of composition Y _2.98 Ce _0.02 Al ₈ O ₁₆ , (y = 2.9), 1200 g of a mixture of powdered oxides of the composition were prepared: Y ₂ O ₃ - 541.2 g, CeO ₂ - 2.76 g, Al ₂ O ₃ - 654.04 g. The mixture was stirred, poured into a molybdenum crucible, which was placed in a heat unit with a tungsten heater from the Sapphire 2MG installation. Melting and directional crystallization of the mixture were carried out in vacuum at a container drawing speed of 4 mm / h. The resulting material is bright yellow, transparent, without inclusions. The photoluminescence spectrum taken from the obtained material during its irradiation with a mercury-quartz lamp had an intensity of 100,000 rel. units at a wavelength of 540 nm (Fig. 2).

Example 3. To obtain a solid solution of composition Y _2.98 Ce _0.02 Al _8.99 O ₁₈ (y = 4) a mixture of powdered oxides weighing 1200 g was prepared: Y ₂ O ₃ - 502.92 g, CeO ₂ - 6, 48 g, Al ₂ O ₃ - 690.6 g. A molybdenum container with the mixture was placed in the Sapphire 2MG unit. Melting and subsequent crystallization were carried out in vacuum at a container drawing speed of 4 mm / h. An opaque material is obtained that weakly luminesces in the region of 380 nm.

From the above examples, the possibility of obtaining a solid solution of aluminum oxide and yttrium-aluminum garnet with cerium is obvious.

Using the proposed phosphor material makes it possible to double the intensity of photoluminescence in combination with its high stability in changing climatic conditions, which can significantly expand the scope of white LEDs.

Claims (1)

Monocrystalline phosphor material for white light emitting diodes, including yttrium-aluminum garnet activated by cerium, characterized in that it is a solid solution of aluminum oxide and yttrium-aluminum garnet with cerium and has a composition corresponding to the formula
Y _3-x Ce _x Al _{5 + y} O _{12 + 1.5y,}
where x = 0.02-0.05,
y = 0.17-3.97.

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