Papers by Author: Robert Fedyk

Abstract: Y3Al5O12:Nd3+ nanoceramics were obtained by sintering nanocrystalline Y3Al5O12:Nd3+ powders at 450 oC under different pressures between 2 and 8 GPa. The structural purity, residual stress, strain, texture, and crystallite size of the products were analysed with X-ray powder diffraction. The results indicate that the average crystallite size remains unchanged at about 30 nm in spite of the heating and the pressure applied. No texture was observed. On the other hand, the microstrains increase with increasing pressure, while the residual stresses are at their maximum in the green body and the sample processed at 8 GPa. Increasing strains were observed to increase the width of the luminescence lines and to decrease the luminescence decay times.

Abstract: Time-resolved luminescence characteristics have been studied for cerium doped YAG nanopowders (NP) and nanostructured ceramics (NC). The results obtained have been compared to the luminescence characteristics for the well studied YAG:Ce3+ single crystal (SC). It was detected that the luminescence decay kinetics of Ce3+ related emission in nanocrystals can be closely approximated by two exponents, whereas a single exponential decay was observed in the single crystal. It was also found that the luminescence decay time and light yield of Ce3+ emission are strongly dependent on the cerium concentration and an unusual concentration quenching of Ce3+ emission was observed in YAG nanocrystals. The origin of the differences of luminescence characteristics for cerium doped nanocrystals and SC are discussed. It is suggested that there are special Ce3+ sites which are closely related to the surface states and that they have a strong influence on the luminescence properties of cerium doped YAG nanocrystals.

Abstract: The preparation of transparent nanoceramics from nanocrystalline Y3Al5O12 (YAG) powders doped with rare-earth ions has been described and the results of investigation of the structure and morphology have been presented. Decomposition of YAG nanocrystals into YAlO3 (YAP) was observed. The temperature and pressure for the decomposition was much lower than that reported for larger crystals. The transformation was connected with grain coarsening. The influence of the method of preparation of the YAG nanopowders on the final transparency of the nanoceramic produced was determined. Preliminary results of the dependence of luminescence properties on the structural transformation of the nanograins are presented.