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Yttrium (Y2O3) nanopowders were synthesized via the precipitation method using ammonium hydrogen carbonate (AHC) as the precipitant. The influences of calcination temperature on the composition and morphology of the powders were investigated. Fine Y2O3 powders with low-agglomeration were obtained by calcining the precursor at 1100 °C for 4 h. The primary crystallites were calculated to be ∼47 nm in size and weakly agglomerated to particles with size of ∼79 nm. Using the synthesized powders as the starting materials, Y2O3 ceramics were fabricated by vacuum sintering at different temperatures combined with HIP post-treatment. The densification and micro-structure evolution of the Y2O3 ceramics were systematically investigated. The ceramic sample vacuum sintered at 1500 °C for 2 h and post-HIPed at 1550 °C for 3 h exhibited a uniform and fine microstructure with the average grain of about 1.0 μm. The in-line transmittance of the ceramic sample reached 80.1% at 1100 nm.

Ytterbium-doped yttrium oxide (5 at.%Yb:Y2O3) nanopowders were synthesized by the co-precipitation method in this work. The influence of the molar ratio of ammonium hydrogen carbonate to metal ions (NH4HCO3/M3+, defined as R) on the properties of the precursors and powders was studied. The powders calcined at 1100 °C from the precursors with different R showed the same phase as the pure cubic Y2O3. However, the agglomerations of the calcined powders were influenced by the R evidently and the 5 at.%Yb:Y2O3 powders with R = 4.0 showed better dispersivity. Using the obtained powders as starting materials, 5 at.%Yb:Y2O3 transparent ceramics were fabricated by vacuum sintering and hot isostatic pressing (HIP) post-treating. The 5 at.%Yb:Y2O3 ceramics with R = 4.0 possessed the best optical quality with the in-line transmittance of 81.2% at 1100 nm with fine grains. In addition, the microstructures of the 5 at.%Yb:Y2O3 transparent ceramics with different R values were also studied and the HIP post-treated ceramics exhibited homogeneous microstructures. Meanwhile, the absorption and emission cross-sections of the 5 at.%Yb:Y2O3 ceramics were calculated to be 0.99 × 10−20 cm2 at 976 nm and 0.97 × 10−20 cm2 at 1031 nm, respectively. The gain spectra also were obtained from the absorption and emission spectra.

Single-phase 2Gd2O3·(Gd,Tb)2(SO4)3·nH2O precursor with strong crystallinity was synthesized by the water-bath method through optimizing the introducing method of Tb3+ doping, where Tb3+ was introduced from Tb(NO3)3. The formation process and phase evolution of the precursor were analyzed in detail. Compared with the conventional method of introducing Tb3+ via Tb4O7, the inhomogeneous doping caused by the appearance of 2Tb2O3·(Gd,Tb)2(SO4)3·nH2O in the precursor was avoided. Pure Gd2O2S:Tb nanopowders with layered structure were obtained after calcination in flowing H2-Ar. The Gd2O2S:Tb powder prepared with Tb(NO3)3 has higher XEL intensity than that with Tb4O7. Using the synthesized powders as starting material, Gd2O2S:Tb scintillation ceramics with high relative density (over 99% of the theoretical value) were fabricated by vacuum pre-sintering and HIP post-treatment in an argon atmosphere. The influences of the introducing method of Tb3+ doping on the microstructure, photoluminescence and X-ray excited luminescence of the Gd2O2S:Tb ceramics were studied. The ceramic sample prepared with Tb(NO3)3 has better luminescence properties due to the homogeneous doping in the ceramics. Temperature-dependent XEL measurements imply that the green emission of the ceramic sample is always dominant with the increase of temperature from 77 K to 340 K, attributed to the cross-relaxation between 5D3 and 5D4 levels of Tb3+.

Yb,La:CaF2 nano-powders doped with different Yb3+ concentrations as 1, 2, 3, 5 at.% were synthesized by the co-precipitation method. The Yb,La:CaF2 powders which were in pure cubic CaF2 phase. The Yb,La:CaF2 transparent ceramics were prepared by the air pre-sintering at different temperatures for 2 h with hot isostatic pressing (HIP) post-treatment at 650 °C for 2 h under 62 MPa Ar. The influences of the Yb3+ doping concentration and pre-sintering temperature on optical quality and microstructures of ceramics were investigated. Among all the fabricated ceramics, the 3 at.%La,5 at.%Yb:CaF2 transparent ceramics pre-sintered at 650 °C showed the best optical quality. For the 1 mm thickness sample, its in-line transmittance reached 92.6% at 1200 nm. Furthermore, the absorption and the emission cross sections of the ceramics were calculated. The strongest absorption and emission peaks are around 977 nm. The lifetime for the Yb,La:CaF2 transparent ceramics at 1028 nm increased first and then decreased with further increasing the Yb3+ doping concentrations.

Terbium aluminum garnet (TAG) transparent ceramics were fabricated by solid-state reactive sintering in vacuum combined with hot isostatic pressing (HIP) post-treatment using tetraethoxysilane (TEOS) as sintering aid. The influences of TEOS amount on the densification, microstructure and optical properties of TAG ceramics were investigated. The in-line transmittance of the TAG ceramic with 0.2 wt% TEOS additive, which was fabricated by pre-sintering at 1700 °C for 20 h and HIP post-treating at 1700 °C for 3 h, can reach about 66% in the visible and near-infrared regions. With appropriate amount of sintering aid, the transmittance of TAG ceramics in the visible wavelength range can be improved significantly by prolonging the holding time.