RU2192444C2 - Photoluminophore of long-persistence - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: photoluminophore corresponds to the general formula: Me_1-x-y Mn_xEu_y(Al_1-q-z Y_qLn_z)₂ O₄ where Ln means Nd and/or Dy; Me means the combination Sr-Mg and Ca-Mg, 0.001 <x ≤ 0.002; 0.01 <y ≤ 0.05; 0.005 <z ≤ 0.05; 0.005g ≤ 0.05; ratio y/( x + z ) = from 1:2 to 2: 1. [MgCO₃]/[SrCO₃] = g and [MgCO₃]/[CuCO₃] = g. Photoluminophore shows long-persistence property up to 48 h and enhanced long-persistence brightness for the first 10-30 min after light effect ceasing. Invention can be used in making sources of emergency autonomic illumination, fencings, illuminating, indicators, device scales, road signs. EFFECT: valuable properties of photoluminophore. 2 cl

Description

 The invention relates to the field of materials science, namely to the field of luminescent materials with a long afterglow, which are capable of storing a large amount of energy when irradiated with optical radiation and emit it for a sufficiently long time in the form of optical radiation after the cessation of excitation, and daylight can be used as an excitation source , gas-discharge and incandescent light sources, ultraviolet radiation lamps, etc.

 The duration of the afterglow of such phosphors in a number of cases is quite sufficient for their practical use as emergency stand-alone lighting sources, for indicating emergency exits in extreme situations, fences, for highlighting various signs, including advertising and road, instrument scales, clocks, for designations of elements of road and floor coverings, etc.

Known photoluminophores with a long afterglow based on sulfide compounds of the type (CaS, SrS): Bi or ZnS: Cu, having the general formula A _p B _U1 : Me (see, for example, SU, copyright certificate 1813779). These materials, not having a significant afterglow time, differed at the same time with a fast rate of light accumulation, sufficient initial brightness and the ability to reproduce the basic colors of the palette. To increase the efficiency of phosphorescence, a second activator was often introduced into the composition of sulfide phosphors. So, for SrS, CaS: Bi, the addition of Sm and Cu had a favorable effect, and for ZnS: Cu, the addition of Co. However, the low hydro- and weather-resistance parameters caused the rapid destruction of first-generation phosphors in air, under solar radiation, and in water.

 The practical use of these materials was limited to their use only in closed rooms with constant temperature and humidity.

It is known the use of rare earth elements for the activation of phosphors (RU, patent 2004566). In particular, a luminous phosphor composition was proposed for a sufficiently long time:
K ₂ Y _1-xy Nb _x Yb _y F ₅ ,
where 0.001 <x <0.150;
0.02 <y <0.20.

The second generation of light-accumulating phosphors is known, associated with the use of aluminates of the second main (IIA) subgroup of the periodic System of elements (Ca, Sr, Ba) O: Al ₂ O ₃ . These compounds are formulaic and structural analogues of the natural mineral spinel - MgAl ₂ O ₄ . Effective luminescence in aluminates is ensured by the introduction of activators in the form of rare-earth elements, in particular divalent europium, in a concentration of [Eu ⁺² ] from 1.10 ^-2 to 8 at.%. To significantly increase the duration of the afterglow, a second rare-earth ion, taken from the group of dysprosium, cerium, neodymium, erbium, both individually and in combination, was added to the phosphor in addition to the activator europium. In this case, it is possible to accumulate large light sums that are illuminated for 1-40 hours. Long-time phosphors on an aluminate basis are described in detail in US Pat. No. 5,424,006.

However, aluminate photophosphors of the composition (Ca, Sr) Al ₂ O ₄ : Eu, Dy, despite the relatively high lighting performance, also did not allow reaching the brightness level of the afterglow, which ensured the guaranteed visibility of the information displayed using photophosphors with long afterglow. Therefore, the use of photophosphors in various signs, warning signs, and various information displays remained in question.

 The technical problem solved by the present invention is to create a photophosphor with a long afterglow, which provides increased brightness of the afterglow in the first 10-30 minutes after the termination of the action of exciting light, which also has a long afterglow (up to 48 hours).

 The technical result achieved by the implementation of this invention is to provide the possibility of using photoluminophores in adverse conditions for advertising and preventive needs.

The specified technical result is achieved by the use of paints, mastics and other coatings suitable for use, as well as plastics used to create structural elements for information screens and fences, photophosphors based on calcium and strontium aluminates, activated by manganese, europium, dysprosium, neodymium, and the composition of the phosphor as impurities introduced a combination of multivalent coactivators Mg and Y, with the receipt of the General chemical formula
Me _1-xy Mn _x Eu _y (Al _1-qz Y _q Ln _z ) ₂ O ₄ ,
where Ln is Nd and / or Dy,
Me is a combination of Sr-Mg and / or Ca-Mg,
and the values x, y, q, z correspond to the values:
0.001 <x≤0.002, 0.01 <y≤0.05, 0.005 <z≤0.05, 0.005 <q≤0.05 with the ratio y / (x + z) varying from 1: 2 to 2 :1. Preferably, the relative concentration of the Mg impurity in the photoluminophore corresponds to the values of the initial molar fractions:
[MgCO ₃ ] / [SrCO ₃ ] = q and
[MgCO ₃ ] / [CaCO ₃ ] = q,
where q = 0.005-0.05.

 The proposed composition has a crystalline structure like spinel.

 The indicated combination of activating impurities provides high values of the amount of light accumulated by the photoluminophore upon excitation by the blue-blue radiation of the visible spectrum.

The combination of Mn ^{+ 2} and Nd ⁺³ (Dy ⁺³ ), Y ⁺³ and Mg ⁺² ions determines the spectrum and concentration of electron-hole traps, the depth of which lies in the range 0.5-0.6 eV above the ceiling of the valence band. Such activation energy corresponds to the maximum afterglow intensity under normal external operating conditions for 10-30 minutes after the cessation of excitation.

To obtain a photoluminophore of the optimal composition, 0.910 M SrCO ₃ , 0.04 M MgCO ₃ , 0.920 M Al ₂ O ₃ 0.04 M Y ₂ O ₃ with 0.050 M Eu ₂ O ₃ and 0.040 M Dy ₂ O _{3 were} mixed. Mix the components in a drum mill until complete homogeneity of the original mixture. The resulting mixture is then loaded into crucibles, protected with a layer of activated carbon, closed with a lid and put in a furnace heated to 500 ^{° C.} Raise the temperature in the oven to 1320 ^o C, incubated for 2 hours. Then the crucibles are cooled together with the furnace to 700 ^o C, after which further cooling of the crucible occurs outside the furnace under normal external conditions (T = 20 ^o C). The cooled crucible is broken, the sintered bead is removed and the middle part is extracted from it, which has no extraneous color and has bright photoluminescence.

 Similarly synthesized phosphor samples, the composition of which corresponds to that given in the independent claim, are well photoluminescent when irradiated with daylight and at the same time have intense phosphorescence, which is clearly visible in the dark.

 The Sr-based crystalline matrix is well excited by blue rays and emits green light. The excitation and emission spectra of a matrix based on a calcium cation differ from the corresponding spectra for a matrix based on strontium cations by a shift toward shorter wavelengths. The maximum excitation corresponds to the region of blue-violet rays and is 350-400 nm. The emission spectrum of such a matrix corresponds to blue radiation, which combines well with the visibility curve for twilight vision of a colorimetrically normal human eye.

The phosphorescence studies of the synthesized samples were carried out upon excitation by radiation of a standard D ₆₅ type white light source.

 The time and intensity of the afterglow are weakly dependent on the absorption coefficient of the exciting light. The longer wavelength excitation corresponds, as a rule, to the lower absorption capacity of the photoluminophore, which leads to a lower specific brightness of the glow, but allows the use of more traps in the volume of the phosphor, therefore, the scattered light of the daytime horizon is favorable for the operation of the proposed compositions.

The action of multivalent impurities Mg ⁺² , Y ⁺³ , Mn ⁺² favorably affects the characteristics of photoluminophores made on the basis of strontium and calcium aluminates. Optimum quantities correspond to x = 0.002-0.005 q = 0.02-0.05.

 The proposed photoluminophore can be used in numerous variations of signs and other signs used in emergency situations caused by a sudden loss of light.

 The above photophosphors can be used to create modern emergency light sources, information boards, safety signs used in emergency situations, accompanied by a sudden turn off of light sources and the onset of darkness, loss of visibility due to smoke, fog, etc.

Claims (2)

1. Photophosphor based on calcium and strontium aluminates, activated by manganese, europium, dysprosium and / or neodymium, characterized in that Mg and Y are additionally introduced into the photophosphor as an activator to obtain the general chemical formula
Me _1-x-y Mn _x Eu _y (Al _1-qz Y _q Ln _z ) ₂ О ₄ ,
where Ln is Nd and / or Dy;
Me is a combination of Sr-Mg and Ca-Mg,
and the values x, y, q, z correspond to values of 0.001 <x≤0.002; 0.01 <y≤0.05; 0.005 <z≤0.05; 0.005q≤0.05 with a ratio of y / (x + z), varying within 1: 2-2: 1. 2. The photoluminophore according to claim 1, characterized in that the relative concentration of Mg in the photoluminophore corresponds to the values of the initial molar fractions: [MgCO ₃ ] / [SrCO ₃ ] = q and [MgCO ₃ ] / [Ca CO ₃ ] = q, where q = 0.005-0.05.