RU2194736C2 - Photoluminescent phosphor with overlong-duration afterglow - Google Patents

Abstract

FIELD: luminophors. SUBSTANCE: photoluminescent phosphor, which can be used for emergency and off-line lighting systems, special- destination clothing, astronomic object simulation and highway warning devices, contains II-group element oxides (MeO), alumina, IV-group element oxides (MeO₂), and silica at molar ratio 3:1:2:1, respectively, and, in addition, one rare- earth element. Molar ratio MsO/CaO/SrO ranges from 1:4:5 to 1:2:7. As rare-earth element, photoluminescent phosphor contains at least one element selected from Eu, Sm, and Yb and at least one element selected from Y, Nd, Ce, Er, Ho, Yb, and Gd at atomic ratio of indicated groups of elements between 1: 1 and 3: 1. Photoluminescent phosphor is depicted by formula Ca_3-yAl_2-xSi•Zr₂O₁₂•Eu_yY_x, in which x=0.005-0.01, y=0.01-0.2. Its brightness during 60 min after excitement considerably rises and slowly drops during 12 h. Maximum of thermoluminescence is observed within a temperature range of 350-400 K. EFFECT: enhanced luminescence characteristics and increased hydrolytic stability. 3 cl, 1 tbl, 6 ex

Description

 The invention relates to the field of materials science, specifically to the technique of luminescent materials emitting for many hours after the termination of exposure to exciting light and intended for use in emergency and autonomous lighting systems, in various clothing elements, preferably for special purposes, in devices for simulating astronomical objects, traffic warning structures, etc.

The first generation of photoluminophores (PLs) with a long afterglow was based on sulfide compounds of the CaSBi or ZnSCu type, having the general formula A _p B _U1 Me. These materials were distinguished by a fast light accumulation rate, sufficient brightness and the ability to reproduce various colors of a polychrome palette.

 However, the low stability parameters caused their rapid destruction in air under solar radiation and humidity. Due to the nature of the phosphor matrix, the hydrolytic instability of the first generation photophosphors allowed them to be used only in closed conditions with constant temperature and humidity. So, products with sulfide phosphors were used in book publishing and printing of advertising brochures, books and calendars. They were used to create decorations in theaters, when illuminating various darkened spectacular structures - game caves, full-scale reduced geographical maps, etc. Very often, to give the necessary brightness, products with elements from sulfide photophosphors were additionally illuminated with UV lamps.

The well-known second generation of storage phosphors is associated with the use of aluminates of the second main subgroup of the Periodic system (Ca, Sr, Ba) Al ₂ O ₄ . When such compounds are activated by a pair of rare-earth elements entering into an intracrystalline redox reaction, for example, Eu ⁺² + Dy ⁺⁴ -> Eu ⁺³ + Dy ⁺³ + W _ex. , it is possible at a concentration of [Eu] ⁺² = 1-5% (atom) to accumulate significant amounts of quanta of light radiation that are then displayed for 10-40 hours. Phosphors of the second generation, in particular, are described in patent US 5424006. For a significant increase in duration Afterglow, a second rare-earth ion, taken from the group of dysprosium, cerium, neodymium or erbium, was introduced into the phosphor in addition to the activator europium. Synthesis of a phosphor of the composition Me _1-y Al _2-x O ₄ .Eu _y ⁺² Lu _x ⁺³ , where Me = Ca, Sr, Ba, Lu = Dy, Ce, Nd, Er, and the content of divalent europium varies from 1 • 10 ^-3 to 10% (atom) is produced from a mixture of metal carbonates (respectively from calcium, strontium, barium) and aluminum, europium, and second lanthanide oxides in a reducing medium upon heating for 1 h.

 The main advantages of this phosphor are: the ability to accumulate significant quantities of quanta of optical radiation when illuminated by natural or artificial light; wide spectral range of exciting light from 320 to 490 nm; the possibility of radiation from the accumulated electromagnetic radiation in blue, green or green-yellow color; high temperature (up to 340 K), to which the photoluminophore is able to flash the accumulated radiation; multi-day resistance to the effects of exciting sunlight; the availability of the starting reagents used in the phosphor.

However, the well-known photoluminophore composition Sr _1-y Al _2-x O ₄ • Eu _y ^{+ 2} Dy _x ^{+3 of the} second generation had significant drawbacks: low stability in the aquatic environment, low resistance to high ambient temperatures. So, when the paint is heated on a metal substrate to 100 ^o With it loses up to 60% of the initial brightness. In addition, the technology for the production of photoluminophors from Sr _1-y Al _2-x O ₄ • Eu _y ^{+ 2} Dy _x ⁺³ requires the use of very high temperatures in the synthesis (T _synth > 1300 ^o C), a closed reducing medium, which, of course, increases the cost of the final product and reduces the reproducibility of its lighting properties.

 The technical problem solved by the present invention is to create a storage photoluminophore with high brightness and dynamic properties, high operating temperature and hydrolytic stability while maintaining fully all the primary advantages of aluminate photoluminophore with ultra-long afterglow.

 The technical result obtained by the implementation of the invention is to expand the scope of phosphors by increasing resistance to external influences.

A composition of a photoluminophore matrix based on aluminum oxide Al ₂ O ₃ and oxides of the main subgroup of group II of the Periodic system of elements is proposed, additionally containing oxides of the main and secondary subgroup of group IV of the Periodic system, taken from the group SiO ₂ , TiO ₂ and ZrO ₂ when the general formula 3MeO is reached • 2MeO ₂ • Al ₂ O ₃ • SiO ₂ .

и отличается относительно низкой температурой плавления Т= 1850^oС, что обуславливает также понижение температуры ее синтеза из компонент.The proposed matrix composition has a cubic crystal structure with a lattice parameter close to a =

and has a relatively low melting point T = 1850 ^o C, which also leads to a decrease in the temperature of its synthesis from the components.

 High lighting and light storage properties of the proposed photoluminophore are realized only with a thorough synthesis of this material. For this operation, specially prepared materials of high purity are used.

 The following are examples of the implementation of the invention.

Example 1. Mix 3M CaCO ₃ + 2M ZrOCl ₂ • 8H ₂ O + 1M SiO ₂ + 1M Al ₂ O ₃ + 0,001 Eu ₂ O ₃ + 0,005MY ₂ O ₃ , grind them until completely homogeneous. The charge loaded into a 2 liter (2000 ml) alundum crucible tamped bulk density to 1.2 g / cm ^3, a crucible lid closed and loaded into a heated to 500 ^o C oven with a reducing atmosphere. The rate of temperature rise in the furnace is 10 ^o / min.

The mixture is aged in the furnace for 120 minutes at T = 1320 ^o C, after which the furnace is cooled to 700 ^o C. The contents of the crucibles are quenched by cooling in running distilled water. The phosphor bead is disassembled under a UV lamp, a part of the bead that is brightly glowing with bluish-green light is separated from the dark surface part. It should be noted low sintering ability of the product.

The luminous part of the peel is further dispersed in a drum mill (the ratio of the phosphor mass to the mass of balls is selected within 1: 3) for 1-2 hours, after which the material parameters are measured with dosed external illumination and a timer. The formula composition of the synthesized material is written as
Ca _3-y Al _2-x Si, Zr ₂ O ₁₂ | Eu $\genfrac{}{}{0ex}{}{\text{+2}}{\text{y}}$ + Y $\genfrac{}{}{0ex}{}{\text{+3}}{\text{x}}$ .
Its cumulative characteristics, depending on the concentrations of introduced Eu ⁺² and Y ^+3, are given in the table.

Upon primary excitation for 5 min with 200 lux illumination, the photoluminophore accumulates a light sum sufficient to illuminate for 16 hours (Sample 1-3). Hydrolytic stability is controlled by immersion of the phosphor powder in water and determining the concentration of hydrogen ions (pH), while the pH of the aqueous extract remains in solution at a level of 6.9-7.5 pH units for 10 hours, while the known material Sr _1-y Al _2-x O ₄ • Eu _y ^{+ 2} Dy _x ⁺³ usually has an alkaline reaction (pH = 9.5) and goes into a jelly-like state within 1 hour.

Example 2. 1.5 M CaCO ₃ + 0.5 M MgCO ₃ + 1 M SrCO ₃ + 2 M ZrOCl ₂ • H ₂ O + 1 M SiO ₂ + 1 M Al ₂ O _{3 are} mixed together with 0.005 M Eu ₂ O ₃ and 0.005 M Nd ₂ About ₃ . The mixture was triturated for 2 hours. The mixture was loaded into a silicon carbide crucible and heated to 1320 ^{° C.} for 3 hours in a reducing atmosphere, after which it was cooled and held for 800 hours at 800 ^° C.

After cooling, the mixture is quenched in water with T = 5 ^o C, the bead is disassembled under a UV lamp and washed from non-luminous particles. Korolek is crushed in a high-speed (1500 rpm) grinder with simultaneous fractionation and transfer to the regeneration of a coarse phosphor.

After crushing and sieving, the parameters of the phosphor are measured, which, under standard excitation conditions, has an initial brightness value of more than 3000 millikandel / m ² and retains a residual luminosity of 40 millikandell / m ² for 2 hours. The formula of the phosphor is written as Ca _1.5 Mg _0.5 Sr _0.99 Al _1.99 Si, Zr ₂ O ₁₂ Eu _0.01 Nd _0.01 . Phosphor grains have an average diameter of about 15-20 microns, large aggregates and particles larger than 40 microns are practically absent in the mass of grains.

Examples 3, 4, 5. In the composition of the charge injected 2M CaCO _3, MgCO _3, 0.4M, 0.6M SrSO _3, ZrO • 2M SO ₄ • 6H ₂ O, 1M SiO _2, 2M Al (OH) ₃ and 0, 01M Eu ₂ O ₃ . The mixture of the starting components is thoroughly mixed with a vibrating mill. Samples differ by the introduction of various amounts of holmium oxide by weight from 0.004 M, 0.01 M and 0.015 M. The mixture is additionally carefully rubbed to obtain an average diameter of d ₅₀ <3 μm. The mixture is loaded into a crucible from sintered alundum, ramming to a bulk density of ~ 1.3 g / cm ³ . The crucible is closed with an alundum lid.

The crucible with the charge is loaded into a furnace heated to 600 ^{° C.} with a reducing medium and silica elements. The rate of temperature rise in the oven is up to 10 ^o / min, the oven is heated to 1320 ^o C, and then held for 2 hours. The synthesized product is cooled with the oven, crushed in a jaw mill, and then sieved through a sieve with a mesh size of 400 microns .

Phosphor grains are treated from the surface with an aqueous solution of silica sol, which is the product of an ion-exchange reaction between K ₂ O • SiO ₂ and a cation exchange resin. The phosphor acquires the property of hydrophilicity and is easily combined with various water-dispersion varnishes and enamels.

Initial brightness sample corresponding to the composition 3 may reach 5 cd / m ² (F = 200 lux), the composition of 4 - 4.6 cd / m ^2, the composition of 5 - 4.2 cd / m ^2. The attenuation for all samples to a level of 1 mcd / m ² exceeds 12 hours

Example 6. Mix in a drum
2.78 M SrCO ₃ , 0.1 M MgCO ₃ , 0.1 M CaCO ₃ , 2 M ZrO ₂ , ₁ M SiO ₂ , 0.92 M Al ₂ O ₃ , 0.08 M B ₂ O ₃ , 0.01 M Eu ₂ O ₃ , 0.01 M Er ₂ O ₃ . The mixture is distributed over alundum crucibles and closed with a lid on top.

Calcination is carried out at 1330 ^o C for 2 hours in a reducing atmosphere, after which the phosphor bead is “quenched” in running water and dried. The phosphor is crushed for 4 hours in a planetary mill, sieved through a metal sieve with a mesh size of 40 microns (500 mesh).

After exposure for 15 min (F = 200 lux), the phosphor gains a luminosity of L = 4 cd / m ² , which slowly decreases according to the hyperbolic law to 1 mcd / m ² over 12 hours. PH of the aqueous extract of the sample pH = 6.8 units.

The formula of the phosphor is written as
Si _2.78 • Mg _0.1 Ca _0.1 Al _1.82 B _0.16 Si ₁ • Zr ₂ • O ₁₂ • Eu _0.02 • Er _0.02
An extremely important feature of the proposed compositions is the possibility of combining them with the conditions of daytime and twilight observations of information, when the spectral curve of the sensitivity of the human eye has a short-wavelength shift. For the main sample described in example 1, the curve of long attenuation was taken for 20 hours or more. It was shown on a number of samples that long-term attenuation over a wide time interval is described by the Becquerel-Antonov-Romanovsky hyperbolic equation, in which the power exponent k is close to unity.

где L_p - яркость послесвечения, кд/м²,
α, β, k - коэффициенты,
t - время,
Е - освещенность, люкс.

where L _p is the brightness of the afterglow, cd / m ² ,
α, β, k are the coefficients,
t is the time
E - illumination, lux.

 As noted above, all synthesized materials have insignificant hydrolytic activity; the pH of the aqueous extract remains almost unchanged even when the aqueous phosphor suspension is boiled, which allows using the material with almost any aqueous dispersion varnishes.

Along with hydrolytic stability, the proposed photoluminophore compositions also differ in high lighting and temperature properties. The maximum thermal emission of materials is in the range from 350 K to 400 K, frequency factors - from 10 ¹⁰ to 10 ¹² s ^-1 .

 Despite a certain rise in price of the photoluminophore material as a result of the introduction of zirconium or silicon dioxide into its composition, with significant volumes of its production, the high consumer properties of the photoluminophore will certainly lead to its large-tonnage use.

The developed phosphor can be used in the following areas:
- horizontal and vertical road marking, painting of bridges, protective shields, dividing strips, pedestrian crossings of poles, etc. ;
- emergency emergency lighting systems;
- fire safety systems and warnings;
- light accumulators and solar panels;
- use for painting large structures and structures, such as offshore platforms, mooring walls of port facilities, oil derricks, etc .;
- special clothing, clothing for schoolchildren and divers, etc. etc.

 The ability to light accumulation when exposed to ionizing radiation (x-rays, gamma rays) allows the widely used material in the technique of dosimetric control of various cargoes, mail attachments, etc.

 The widespread use of the material in the technique of accumulating and converting sunlight will be undoubted.

Claims (3)

1. Photoluminophore with ultra-long afterglow, containing aluminum oxide, silicon oxide, oxides of elements of the main subgroup of the second group of the Periodic system of elements and a rare earth element, characterized in that it additionally contains oxide of the element of the fourth group with a molecular ratio of MeO: Al ₂ O ₃ : MeO ₂ : SiO ₂ = 3: 1: 2: 1, moreover, at least one element from the group including Eu, Sm, Yb, and at least one of the elements belonging to group Y is used as a rare-earth element, Nd, Ce, Er, But, Yb, Gd.  2. The photoluminophore according to claim 1, characterized in that, as the oxides of the elements of the main subgroup of the second group, it contains oxides of magnesium, calcium and strontium in a molar ratio of 1: 4: 5 to 1: 2: 7.  3. The photoluminophore according to claim 1 or 2, characterized in that the atomic ratio of elements of the Eu, Sm, Yb group and elements of the Y, Nd, Ce, Er, Ho, Yb, Gd group is from 1: 1 to 3: 1.

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