RU2506301C2 - Luminescent material for solid-state white light sources - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to lighting engineering and can be used in blue LEDs of solid-state white light sources. The luminescent material based on yttrium aluminate, which contains cerium oxide, has the general formula (Y_1-xCe_x)_3±αAl₅O_12+1.5α, where x is the atomic fraction of cerium which is equal to 0.01-0.20; 0<α≤0.5 or 0>α≥-1.5. The colour temperature of the solid-state white light source varies from 3500 K to 4500 K.

EFFECT: colour coordinates and brightness are comparable with commercial samples.

3 cl, 1 tbl

Description

The invention relates to the field of lighting engineering and, in particular, to luminescent materials that glow when excited by blue light in the yellow-orange region of the spectrum and are used in solid-state white light sources. In these devices, intense white light is obtained as a result of a combination of yellow-orange luminescence of the phosphor with the primary blue radiation generated by an LED emitting in the blue region of the spectrum (440-480 nm).

The effectiveness of the devices of this type depends on the chemical composition of the phosphors used, which can be used silicate, phosphate, oxide, aluminate, nitride and oxo-nitride phosphors and their mixtures [C. Ronda Luminescence: From Theory to Application. Science. 2007, 2b0r]. The most effective among them are aluminate phosphors with a garnet structure, formed with the participation of oxides of yttrium, gadolinium, and other rare earth elements, activated by cerium, designated in the literature - YAG: Ce.

A broadband phosphor with a yellow-orange glow based on yttrium-aluminum garnet activated by cerium (Y, Ce) ₃ Al ₅ O ₁₂ and the method for its preparation was first patented as a cathodoluminophore for cathode ray tubes by Philips staff J. Blasse ( G. Blasse) and A. Brile in a number of countries, including the USA: Pat. US 3564322 (US Class: 313/468; Intern'l Class: C09K 11/77) dated 02.16.1971 with primary priority 04/29/1967. The synthesis of this phosphor is carried out by calcining a mixture of yttrium, aluminum and cerium oxides in a reducing medium, which leads to the formation of a compound in which the Y ³⁺ ion is partially replaced by Ce ³⁺ . Thus, Blasse-Bril garnet is a compound of fixed stoichiometric composition with partial substitution of yttrium for cerium in the concentration range from 0.01 to 0.20:

Since 1997, a phosphor with a yellow-orange glow based on yttrium-aluminum garnet activated by cerium has become widely used as a luminescent material for solid-state white light sources. In this case, the attention of the inventors was focused solely on the creation of more complex compositions of various compositions, including two or more lanthanides replacing yttrium.

Between 1998 and 2008, the Japanese company Nichia obtained a series of patents for a device consisting of an InGaN semiconductor heterojunction emitting light with a wavelength of 450-470 nm and coated with grains of a fluorescent substance with the structure of yttrium-aluminum garnet activated by cerium [US Patents No№: No.5998925 (US Class: 313/503; Intern'l Class: H01J 001/62) dated 12/07/1997, No 6069440 (US Class: 313 / 486,489; Intem'l Class: H01L 033/00) from 05/30/2000, No. 6608332 (US Class: 257/98) dated 08/19/2003, No. 6614179 (US Class: 353/512; Intern'l Class: H01L 33/00) dated 08/19/2003, No. 7362048 (US Class: 313/512].

In all of these patents, the authors consider the use of a composition whose composition corresponds to the formula:

(Y _1-x ∑ Ln _x ) (Al _1-abc G _a In _b ) ₅ O ₁₂ , where, among the main rare-earth elements, yttrium, gadolinium, and cerium are mentioned, along with Lu, Sm, La, Sc.

Subsequently, formulations were announced comprising 5 to 14 lanthanides US 20080116422 (US Class: 252 / 301.4R; Intem'l Class: C09K 11/08) dated 05/22/2008 and US 20080290355 (US Class: 257/94; Intem'l Class: C09K 11/08) from 11/27/2008. In the first of these, a composition is proposed whose formula is [Y _1-xyzpq Gd _x Tb _y Yb _z Lu _p Ce _q ] _s Al ₅ O ₁₂ , in addition to Gd, Ce, Lu, Sm Tb, Yb were added. In the application US No. 2008290355 by the same authors, the phosphor composition is given by the formula [Y _1-xyzq Gd _x Lu _y Yb _z Eu _q + activating additives Ce, Pr, Dy, Er, Sm] ₃ Al ₅ O ₁₂ , where lanthanides were included in the group 9 out of 14 f-elements.

жестко фиксировано и равно

.The chemical composition of these phosphors corresponded to the stoichiometric formula (Y + ∑ Ln) ₃ [∑ Ме ³⁺ ) ₅ O ₁₂ , where Ln = Gd, Се and, together with them, one or more elements from the group of lanthanides; Me ³⁺ - aluminum or together with it one or more elements from the group Ga, In, Sc. Moreover, the ratio between

rigidly fixed and equal

.

It should be noted that a key role in the formation of the luminescent properties of yttrium-aluminum garnets is played by Ce ³⁺ ion, which is an activator of luminescence, i.e. an element in which optical transitions determine the color of the glow, and the concentration sets the brightness of the luminescence.

Elements Gd, Tb and Lu are classified as additives that form a luminescent matrix. They provide a shift in the position of the maximum in the luminescence spectrum to the long-wave (Gd, Tb) or short-wave (Lu) spectral regions (Ga, In, Sc can play a similar role). Other rare-earth elements Nd, Eu, Dy, Er, But, Tm, - play an auxiliary role, which was noted in a number of patents, but was not characterized at a quantitative level. The total number of patented compositions of complex cationic composition with fixed stoichiometry (3-5-12) is in the tens.

In the last 5–7 years, patent solutions have appeared in the literature, in which compositions were proposed with altered stoichiometry between the oxides of rare-earth elements and aluminum oxide, both in the direction of excess of rare-earth elements and in the direction of excess aluminum.

In the period from 2001 to 2003, employees of the General Electric Corporation filed 5 patents for terbium, lutetium and terbium-lutetium garnets: US Pat No. 6598195 (07.22.2003), 6630077 (07.10.2003), 6793848 (09.21.2004), 6936857 (08.30.2005) and 7008558 (03.03.2006), the first of which was fundamental. In this document, possible variations of the index value for (∑Ln) _a and (∑Al, Ga, In) _z , were designated, respectively, as 2.8 <a <3 and 4 <z <5. It is worth noting especially the fact that the authors of the patent, changing the indices for ∑Ln and Al, i.e. speaking essentially of a non-stoichiometric garnet, the oxygen index is written to 12. If we take into account that the charge state of all metals characterizing the specific composition of the declared phosphors corresponds to the Me ³⁺ state, then the oxygen index of 12 is preserved if single-phase composition only under the condition that the charge state of representatives of the lanthanide group will be more than 3. The latter is in principle excluded, since the preparation of the phosphor is carried out under reducing conditions (high temperatures tours and the presence of hydrogen), when the stable state for terbium and cerium is 3+.

In the latest patent of General Electric Corporation (7008558 (03/07/2006)) the composition is represented by the formula: (G _1-xy A _x Rey) _a D _z O ₁₂ , where the variations of the stoichiometric indices “a” and “z” are indicated inequalities 2.8 <a <3.1 and 4 <z <5.1 (preferably: 2.884 <a <3.032 and 4.968 <z <5.116).

In 2006, a patent was issued (US No. 7135129 (US Class: 252 / 301.4R; Intern'l Class: C09K11 / 08 of 11/14/2006 for a phosphor composition: (Y _1-xyzq Gd _x Dy _y Yb _z Er _q Ce _p ) _α (Al _1-nmk Ga _n Sc _m In _k ) _β O ₁₂ , the stoichiometric indices for which α and β were equal: α = 2.97-3.02 and β = 4.98-5.02). In the application US20090153027 (US Class: 313 / 503; Intern'l Class: C09K 11/78) dated 06/19/2009 a phosphor having the composition [Y _2-xyzq Gd _x Ce _y Pr _z Dy _p O ₃ ] _{1,5 ± α} + (Al ₂ O ₃ ) _{2 is} proposed _{, 5 ± β} ), where α = (0.01-0.1) and β = (0.01-0.1). According to the authors, the preferred index values are 0.01 for "α" and 0.03 for "β".

In patent applications (WO 2011/014091 A1 and PCT / RU 2010/000619) compositions were proposed in which the index values for the elements of the yttrium sublattice varied in the range from 3.03 to 5 (excess yttrium oxide) and, accordingly, from 2, 8 to 1.0 (excess alumina). As it turned out, phosphors, in which the index value differs from the corresponding stoichiometric garnet (3), were not inferior in their operational properties, but in a number of signs (sintering ability, cost, brightness, color coordinates) are superior to those possessed by grenades with stoichiometry “3- 5-12 ".

However, no matter what the phosphor composition was stoichiometric or non-stoichiometric, the luminescent materials declared after Blaise-Bril always contained, in addition to cerium, at least one more lanthanide, which only corrected the activating effect of cerium. Therefore, if we do not consider the shift of the maximum to one side or another of the spectrum (almost always leading to a decrease in brightness), then we can assume that the simplest stoichiometric Blassse-Brill garnet possesses a set of properties necessary for practical application.

As a prototype of the invention, the patent RU No. 2396302 was selected, which describes the use of stoichiometric yttrium aluminum garnet (Y _1-x Ce _x ) Al ₅ O ₁₂ , activated only by cerium and designed to convert the radiation of blue LEDs in order to obtain solid-state white sources Sveta.

The disadvantage of the prototype is that within it can be synthesized a limited number of phosphors that differ only in the concentration of cerium.

The objective of the invention is to expand the range of inorganic luminescent materials for solid-state white light sources.

The problem is solved by creating a new luminescent material for solid-state white light sources based on yttrium aluminate, including yttrium oxide, cerium oxide, and aluminum oxide, while the composition of the inorganic luminescent material corresponds to the general formula (Y _1-x Ce _x ) _{3 ± α} Al ₅ O _{12 ± 1,5α} ,

where x is the atomic fraction of cerium equal to 0.01-0.20;

α is a value characterizing the deviation from the stoichiometric index 3 in yttrium garnet, both in the direction of values> 3, corresponding to positive values of α, and values <3, corresponding to negative values of α.

The positive values of α correspond to the introduction of an excess of yttrium oxide with respect to alumina compared with a ratio of 1.5: 2.5 in the stoichiometric compound (Y _1-x Ce _x ) ₃ Al ₅ O ₁₂ , which leads to an increase in the oxygen index to a value 12 + 1,5α. Negative values of a correspond to a lack of yttrium oxide with respect to alumina compared with a ratio of 1.5: 2.5 in the stoichiometric compound (Y _1-x Ce _x ) ₃ Al ₅ O ₁₂ , which leads to a decrease in the oxygen index to 12 -1.5α. In this case, the positive values of the index a vary in the range 0 <α≤0.5 and the negative values in the range 0> α≥-1.5

тогда как в прототипе оно фиксировано и составляет 0,6.Thus, in contrast to the prototype in the present invention, the ratio of molar amounts varies in a wide range of compositions

whereas in the prototype it is fixed and is 0.6.

Case Studies

, а именно: (Y_1-xCe_x)_1,5 Al₅O_9,75, (Y_1-xCe_x)_2,8 Al₅O_11,70, (Y_1-xCe_x)_3,20 Al₅O_12,30 и (Y_1-xCe_x)_3,50 Al₅O_12,75. При переходе от одной серии к другой - содержание церия уменьшалось и составляло х=0,15, 0,10, 0,05 и 0,01. Данные, характеризующие изменение свойств в пределах каждой серии, разделены в приведенной ниже таблице пробелом.Four series of samples were prepared with a given (within this series) cerium content and a varying molar ratio

namely: (Y _1-x Ce _x ) _1.5 Al ₅ O _9.75 , (Y _1-x Ce _x ) _2.8 Al ₅ O _11.70 , (Y _1-x Ce _x ) _{3, 20} Al ₅ O _12.30 and (Y _1-x Ce _x ) _3.50 Al ₅ O _12.75 . In the transition from one series to another, the cerium content decreased and amounted to x = 0.15, 0.10, 0.05, and 0.01. Data characterizing the change in properties within each series are separated by a space in the table below.

Thus, a total of 16 samples were prepared, differing from each other by the index value (3 ± α), as well as the cerium content. Data on the composition of the phosphors are shown in table No. 1. Examples included also sample No. 17, the composition of which corresponds to the prototype.

Phosphors, the composition of which is given in the list of examples, were obtained by heat treatment of a mixture of yttrium, cerium and aluminum hydroxide oxides. The prepared mixtures were calcined in the presence of mineralizers (fluxes), contributing to an increase in the mass transfer rate due to the formation of a liquid phase on the surface of reacting solids, and thereby leading to an increase in the rate of formation of the target product by reactions

Mixtures of barium chloride and fluoride (up to 7-10% by weight of oxides) were used as fluxes.

The starting materials (yttrium and ceria-IV oxides and aluminum hydroxide) with a known particle size distribution (laser particle size analyzer) were mixed dry on a vibrating stand or in a drunken barrel type mixer in closed polyethylene vessels using steel balls with a polyethylene coating . Calcination was carried out in alundum crucibles (Al ₂ O ₃ ) with gradual heating of the reagents in a reducing medium (N ₂ + H ₂ ) at a speed of 7-10 deg / min to a temperature of 1450 ° C. The exposure time at high temperature was 3-5 hours, after which the crucibles were cooled to 400 ° C for 2.5 hours.

To remove the melt, the prepared samples were washed several times with a large volume of distilled water and dried in an oven at 130 ° C. The particle size of the prepared phosphors was about 7-12 microns.

The lighting parameters of the samples were measured on a certified EVERFINE-HAAS device with reflection of blue radiation from synthesized phosphors with yellow-orange glow. The values given in the table correspond to the parameters characterizing the luminescent properties of the samples in the wavelength range 470-780 nm, i.e. minus the blue light emitting diode.

Table number 1 PRODUCT CHARACTERISTICS: I _rel.ed - relative brightness; λ _dom , nm - the dominant wavelength in the luminescence spectrum; λ _peak , nm — position of the maximum in the luminescence spectrum; Δλ _0.5 , nm - width of the luminescent band at half the height of the maximum ordinate; T _c - color temperature, K No. p / p Phosphor composition 1 Characteristics of the yellow-orange luminescence band (470-750 nm) I, rel. λ _dom , nm λ _peak , nm Δλ _0.5 , nm Color coordinates T _c x y one (Y _0.85 Ce _0.15 ) _1.50 Al ₅ O _9.75 499 568.4 543.2 113.1 0.425 0.548 4028 2 (Y _0.85 Ce _0.15 ) _2.80 Al ₅ O _11.70 526 568.5 546.3 112.5 0.427 0.549 4005 3 (Y _0.85 Ce _0.15 ) _3.20 Al ₅ O _12.30 527 568.9 546.8 112.6 0.430 0.547 3956 four (Y _0.85 Ce _0.15 ) _3.50 Al ₅ O _12.75 538 568.9 547.9 113.2 0.429 0.547 3962 5 (Y _0.90 Ce _0.10 ) _1.50 Al ₅ O _9.75 502 570.8 556.5 115.3 0.443 0.537 3730 6 (Y _0.90 Ce _0.10 ) _2.80 Al ₅ O _11.70 506 571.9 557.6 115.7 0.452 0.532 3584 7 (Y _0.90 Ce _0.10 ) _3.20 Al ₅ O _12.30 506 572.1 559.2 115.4 0.453 0.531 3558 8 (Y _0.90 Ce _0.10 ) _3.50 Al ₅ O _12.75 517 571.3 557.6 115.1 0.447 0.535 3658 9 (Y _0.95 Ce _0.05 ) _1.50 Al ₅ O _9.75 487 572.0 558.8 117.2 0.452 0.531 3581 10 (Y _0.95 Ce _0.05 ) _2.80 Al ₅ O _11.70 514 572.6 558.4 116.3 0.457 0.528 3493 eleven (Y _0.95 Ce _0.05 ) _3.20 Al ₅ O _12.30 509 572.5 558.8 116.4 0.456 0.529 3513 12 (Y _0.95 Ce _0.05 ) _3.50 Al ₅ O _12.75 501 572.0 556.9 116.1 0.453 0.531 3568 13 (Y _0.99 Ce _0.01 ) _1.50 Al ₅ O _9.75 403 565.4 534.3 111.3 0.403 0.559 4385 fourteen (Y _0.99 Ce _0.01 ) _2.80 Al ₅ O _11.70 445 565.7 535.5 110.8 0.405 0.558 4353 fifteen (Y _0.99 Ce _0.01 ) _3.20 Al ₅ O _12.30 438 565.7 532.7 110.9 0.405 0.557 4358 16 (Y _0.99 Ce _0.01 ) _3.50 Al ₅ O _12.75 430 566.1 535.4 111.5 0.408 0.556 4309 17 (Y _0.95 Ce _0.05 ) _3.00 Al ₅ O _12.00 486 568.0 547.0 115,2 0.422 0.549 4069

As can be seen from the data in the table, the vast majority of the prepared compositions with the exception of samples of the series with a minimum cerium content exceed in brightness and color characteristics the values that correspond to the prototype.

Claims (3)

1. Luminescent material for solid-state white light sources based on yttrium aluminate, including cerium oxide, and corresponding to the general formula (Y _1-x Ce _x ) _{3 ± α} Al ₅ O _{12 + 150α} , where x is the atomic fraction of cerium equal to 0, 01-0.20;
α is the value characterizing the deviation from the stoichiometric index 3 in yttrium garnet, both towards values> 3 corresponding to positive values of α, and values <3 corresponding to negative values of α, while positive values of α correspond to changes in the indices of oxygen in the range of 12 + 1,5α ”and“ 12-1,5α ”in the case of negative values of α. 2. The luminescent material according to claim 1, characterized in that the value of α is positive and varies in the range of values 0 <α≤0.5, excluding from the set of possible values the value α = 0. 3. The luminescent material according to claim 1, characterized in that the value of α is negative and varies in the range of values 0> α≥-1.5, excluding the value α = 0 from the set of possible values.