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1Book of Absracts. "WOMEN IN STEM" International Forum, Tashkent, February 13 - 15, 2024. https://doi.org/10.5281/zenodo.10643244
GLASS CERAMIC FOR WHITE LIGHT EMITTING DEVICES Ekaterina Trusova and Ekaterina Kravcova
Belarusian State Technological University, Belarus trusova@belstu.by https://doi.org/10.5281/zenodo.10838172
Currently for blue LED based light sources production, «blue LED + powdered phosphorus containing organic polymer» arrangement is usually used. The main task of the luminophore is partial transformation of blue radiation into a yellow-green area, which results in the white light effect.
A luminophore is most often an yttrium aluminium garnet (or another compound of garnet structure) that contains impurities of cerium ions and/or other elements. It should be noted that there are other approaches to obtaining white light, but as a rule they are all more difficult to implement and more expensive to produce. Increasing the brightness (power) of a LED-based light source can be reached in two ways: increasing the power of LEDs; increasing the number of LEDs.
This, in turn, leads to increase of heat generation and of size of the diode assembly. Increased heat generation, in its turn, affects the luminescent properties of phosphorus, namely, leads to reduced luminescence intensity, which ultimately results in a change in the spectral characteristics of the light source itself (the blue portion of the spectrum increases).
The use of blue semiconductor lasers could solve this problem due to the possibility of spatial separation of luminophore and emitter. However, in this case use of organic polymer that contains powdered luminophore is impossible due to thermal degradation of polymer under the impact of laser radiation. However, this problem can be solved.
Glass ceramics are unique materials that can combine transparency of glass and the efficiency of the crystalline phase. Production of glass ceramic materials in some cases is much simpler and cheaper than the production of ceramics or single crystals and consists of two main stages: production of glass and its crystallization. Both stages are determined by glass formation temperature and the temperature of garnet phase formation inside the glass matrix.
The aim of research is to develop compositions and technology for production of vitrocrystalline materials based on yttrium-aluminum garnets.
The object of research were glass compositions based on yttrium-aluminum borosilicate system with cerium oxide. Glass was synthesized in corundum crucibles in an intermittently operating gas furnace. The glass melting temperature was 1550±25°C. All the glass compositions are well melted and lightened, they have no foreign inclusions and no traces of lack of fusion.
Thermal analysis was used to determine the ability of the glass to form crystalline phase and to establish the optimal conditions for the thermal treatment of precursor glass. According to data of differential scanning calorimetry, glass was heat treated at the temperatures of 1100-1500°C.
For glass ceramics produced by glass thermal treatment at the temperaturesof 1100°C garnet phase peaks and impurity phases were observed. The increase in heat treatment temperature leads to a decrease in the number of impurity phases. The thin structure of peaks draws special attention.
The observed asymmetry indicates to formation of garnets with different degrees of substitution. It can be assumed that during the heat treatment the first to be formed are garnet nuclei with composition corresponding to the lowest formation temperature.
This results in a local change of the quantitative structure of the glass in the environment closest to the nucleus (a local decrease in the number of some elements and an increase in the other ones). When the new nuclei appear or continue to grow, the existing nuclei are more likely to capture the element or elements in the glass in excess, which increases degree of substitution of the garnet being formed.
Book of Absracts. "WOMEN IN STEM" International Forum, Tashkent, February 13 - 15, 2024. https://doi.org/10.5281/zenodo.10643244
Directional crystallization of glasses for receiving of complex compounds with garnet structure has a high potential first of all due to the possibility of crystallites composition control by modifying the composition of the initial glasses. This approach also may be used for search of new compounds with the garnet structure.
