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Fine powders of yttrium orthoniobate activated by Eu, Sm, Tb, Er have been synthesized by the sol-gel. The synthesized powders have been calcined at different temperatures (1000, 1100 and 1180 °C). Luminescent ceramics (Y 0.96 Еu 0.01 Sm 0.01 Tb 0.01 Er 0.01)NbO 4 were prepared from fine powders by uniaxial hot pressing (UHP) via various technological modes. For the first time, the crystal structure, microstructure, spectral composition, photoluminescence properties of (Y 0.96 Еu 0.01 Sm 0.01 Tb 0.01 Er 0.01)NbO 4 ceramics have been studied depending on the temperature conditions of the synthesis of powders and UHP conditions during sintering of ceramics. The mechanical properties of these ceramics (Young's modulus, microhardness and critical stress intensity factor for the mode I K IC) have been evaluated. [ABSTRACT FROM AUTHOR]

Fine crystalline GdNbO 4 powders have been synthesized by sol-gel method. Usual ceramic technology and hot pressing have been applied to obtain GdNbO 4 ceramic samples. Morphological particularities have been studied in GdNbO 4 ceramics microstructure. Ceramics strength characteristics (strength, Young's modulus) have been evaluated for the first time. A mode I stress intensity factor K IC have been determined (note that the factor is a crack resistance criterion). Photoluminescence characteristics have been compared in GdNbO 4 ceramics before and after vacuum annealing in the visible region. [ABSTRACT FROM AUTHOR]

We have established optimized parameters of technological process for obtaining of translucent luminescent YNbO 4 ceramics by uniaxial hot pressing (UHP). Ultrafine crystalline powders used for this have been synthesized by sol-gel and sintered at three different temperatures. Series of ceramic YNbO 4 samples were obtained from the powders by UHP at three different sintering conditions. Morphological features of the microstructure, mechanical and photoluminescent characteristics in the visible wavelength range have been compared for YNbO 4 ceramic samples obtained at different UHP conditions and controlled with sample prepared by conventional sintering (CS). The most optimal UHP regime for translucent YNbO 4 ceramics obtaining have been chosen. • Ultrafine YNbO 4 powders were prepared by sol-gel and sintered at 3 temperatures. • An optimal regime was chosen for uniaxial hot pressing (UHP) of YNbO 4 ceramics. • The optimal regime is: T sint = 1180 °C, P 1 = 220 kg/cm2, τ sint = 60 min. • Microstructure, mechanical characteristics and photoluminescence were studied. [ABSTRACT FROM AUTHOR]