Структура і люмінесценція літій-германатної склокераміки LI2O-7GEO2, легованої іонами хрому
Abstract
STRUCTURE AND LUMINESCENCE OF THE LI2Ox7GEO2LITHIUM-GERMANATE GLASS-CERAMICS DOPED WITH CHROMIUM IONS
S. Nedilko, V. Boyko, Y. Rybak, M. Trubitsyn, M.Volnyanskii, M. Koptev
Currently, there are searches for ways to increase the efficiency of converting sunlight into electric current, or blue-violet radiation of light-emitting diodes in yellow-red radiation to create effective sources of "white" light. These problems are solved, in particular, by applying to the surface of solar cells, or LEDs, a luminescent coating, in which purple radiation is absorbed and turned into yellow-red. In commercial white LEDs, this coating is usually a polymer composite, where the filler is an oxide compound: yttrium-aluminum garnet doped with cerium ions. In operation, over time and as a result of heating, there is a mechanical degradation of the polymer matrix, which leads to deterioration of the characteristics and failure of the device. Nowadays, as promising for the mentioned purposes, coatings based on oxide matrices are considered, which, in contrast to the polymeric ones, are stable both in time and in the heat load.
The purpose of the study is to study the luminescence properties and structural characteristics of oxide lithium-germanate glass ceramics.
The set of the samples in glass ceramics and polycrystalline states were made using amorphous Li2O-7GeO2glass (LGO) as starting material and then they were studied using luminescence spectroscopy procedure. The X-ray diffraction analysis had revealed that the glass-ceramics state samples are built by the grains of the lithium tetragermanate, Li2Ge4O9, micro/ nanocrystals incorporated into amorphous germanium oxide, GeO2, matrix. When the transition to polycrystalline state occurs the tetragermanate phase crystals vanishes, while heptagermanate crystals, Li2Ge7O15 are formed. The results of luminescent study of the doped with chromium ions materials had confirmed in the whole mentioned above. In fact, luminescence propertied to radiation transitions in Cr3+ionsplaced mainly in tetragermanat, Li2Ge4O9, was found for glass-ceramics state, while such luminescence propertied both to heptagermanate and tetragermanat was found for polycrystalline state. It was shown that just multiphase structure of the chromium doped lithium germanate compounds promotes designing luminescent transformers of violet radiation to the broad band green - red radiation. The studied material scan be used as luminescent thin film covers aimed to menhance effectiveness of the silicon solar cells, or to design white light emitting diodes.
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