Lithium niobate crystal, combining its piezoelectric, nonlinear, electro-optical, and photorefractive properties, along with its stable physicochemical characteristics, has great potential for applications in integrated optics. However, designing thermal field for large-size lithium niobate crystal growth presents considerable challenges, considering the crucible shape being an important factor that significantly influences the crystal growth in which the diameter and height are compulsively restricted to the factors such as load capacity and crystal diameters. In this study, 4-inch congruent lithium niobate crystals were grown by using crucibles with two types of bottom shapes. The impacts of crucible bottom shape on the axial temperature gradient within the crystal and the melt near the crystal-melt interface, and the temperature distribution within the melt below the crystal-melt interface, were analyzed by numerical simulation. The impact of the crucible bottom shape on crystal growth was analyzed in contrast to crystal growth results. It is found that changes in the crucible bottom shape lead to variations in the temperature difference along the crucible sidewall and the temperature gradient within the melt, thereby altering the strength of natural convection in the melt. Compared to crucible with slipped bottom corner, the axial temperature gradient near the crystal-melt interface within the crystal and melt is large when using the crucible with curved bottom corner, and the axial temperature gradient within the melt below the crystal-melt interface is also large, and the natural convection is strong. Therefore, this study helps to solve the problems such as the unwanted crystal growth ridge spreading and the overgrowth of cellular interface.

β-Ga₂O₃ is a novel wide bandgap semiconductor material with excellent performance, which has great potential applications in high power electronic devices and deep ultraviolet detectors. By doping with In³⁺ ions, the bandgap and optical properties of β-Ga₂O₃ can be adjusted, further expanding its application range. In this study, β-Ga₂O₃:9%In and β-Ga₂O₃:15%In single crystals are prepared using high-purity Ga₂O₃ and In₂O₃ as raw materials by the optical floating zone method. When the growth rate is 5 mm/h, the crystals exhibit a phenomenon of transparency loss. Observation under an optical microscope reveals the presence of numerous bubble defects in the crystals, which mainly appearing strip-like and spherical shape. Length of the strip-like bubbles ranges from 50 to 200 μm and extends along the [010] crystal direction. Observation under a scanning electron microscope reveals uniform elemental distribution around the bubbles, with no evidence of impurity element accumulation. These findings suggest that the formation of defects is related to the high-temperature decomposition of In₂O₃, where the generated gas is not timely discharged, entering the crystal interior with the crystallization of the melt to form bubbles. After optimizing the crystal growth process, the problem of opacity caused by bubble defects is effectively resolved, resulting in transparent β-Ga₂O₃:9%In single crystal with a full width at half maximum of the rocking curve as low as 44 arcsec and significantly improved crystalline quality. This study provides a solution for growing high-quality β-Ga₂O₃:In bulk single crystal, laying a foundation for a deeper understanding of its optoelectronic properties.

Y₂O₃ ceramics is widely used as laser medium or optical window due to its excellent physical and chemical properties and high transparency in wide frequency band of 280 nm-8 μm. However, preparation of highly transparent Y₂O₃ ceramics still remains challenge due to its synthetic precursor and nano-powders difficult to meet the requirements. In this work, a spherical monodispersed and submicron-sized Y₂O₃ powder was prepared by a homogeneous precipitation method using yttrium nitrate and urea as raw materials. Structure, phase evolution and morphology of Y₂O₃ precursor and the calcined powder were studied by different methods. The synthesized particle precursor exhibits a sphere morphology with diamension around 330 nm, and Y₂O₃ powder calcined at 800 ℃ for 2 h shows spherical, well-dispersed and uniformed particles with dimension around 260 nm. Based on this spherical Y₂O₃ powder, transparent Y₂O₃ ceramics were fabricated by vacuum sintering at 1780 ℃ using 0.3% (in atom) Nb₂O₅ as sintering additive. The in-line transmittances of Y₂O₃ ceramics with thickness of 1 mm reach 76.9% at a wavelength of 1100 nm and 65.6% at a wavelength of 400 nm. In conclusion, this study provides a new promising method for preparing Y₂O₃ transparent ceramics with excellent properties.

Currently, the preparation of MgAl_1.9Ga_0.1O₄ transparent ceramics which possess excellent optical properties, is still relying on combining aqueous gel-casting and prolonged pressureless pre-sintering. In this work, MgF₂ was used as a sintering additive, and densification process of pressureless pre-sintering was adjusted by a transient liquid phase. MgAl_1.9Ga_0.1O₄ transparent ceramics with different sizes were prepared by dry pressing, pressureless pre-sintering, and hot isostatic pressing treatment. The effects of MgF₂ additive on microstructure, optical, and mechanical properties of the samples were systematically analyzed. The results indicated that MgF₂ melted at ~1230 ℃, contributing to increase of density and grain size of the pre-sintered body, while the residual MgF₂ was oxidized to MgO and dissolved into the MgAl_1.9Ga_0.1O₄ lattice in the subsequent sintering process. The 2.04 mm thick transparent ceramic sample with 0.20% (in mass fraction) MgF₂ has an in-line transmittance of 76.5%-83.4% in the UV and visible regions. Moreover, the sample has high optical quality with low scattering on incident light. In addition, the characteristic flexural strength of this ceramics is 167.1 MPa, which is close to that of the fine-grained MgAl₂O₄ transparent ceramics, but the Weibull modulus (8.81±0.29) is higher. This study provided a new option for the preparation of large MgAl_1.9Ga_0.1O₄ transparent ceramic materials with good optical properties.

Transparent AlON possesses good mechanical and optical properties, which shows great potential for application. However, high fabrication cost seriously restricts its wide usage. To solve this problem, gel-casting and pressureless sintering of transparent AlON was tentatively studied here, with emphasis on low temperature synthesis and anti-hydrolysis treatment of AlON powder. It was found that fine AlON powder could be readily synthesized at a low temperature of 1700 ℃ by a novel carbothermal nitridation technique, using polymer coated AlN/Al₂O₃ mixture as the starting materials. The powder obtained was submicron in size and its hydrolysis resistance could be significantly improved after surface coating with a polyurethane layer. On the basis of these findings, transparent AlON ceramics was successfully prepared through gel-casting and pressureless sintering. The material sintered at 1850 ℃ showed good optical and mechanical properties, with a high in-line transmittance of 83.1%-86.2% from ultraviolet to mid-infrared and three-point bending strength of 310 MPa.

Transparent ceramic materials have excellent strength, hardness and optical properties, which have important application prospect in light-weight transparent protective armor. However, the preparation of transparent ceramic components with large protection area and high transmittance properties is the main challenge to achieve application. In this work, large-size yttrium aluminum garnet (Y₃Al₅O₁₂, abbreviated as YAG) transparent ceramics with low deformation and excellent optical quality were fabricated by reactive sintering in vacuum using domestic high-purity Al₂O₃ and Y₂O₃ powders as starting materials, and the key technologies including dry pressing, calcining, high-temperature vacuum sintering and optical performance were broken through. In addition, as the upgrading of molding and sintering equipment, the dimension of YAG transparent ceramic was enlarged to 1040 mm×810 mm×15 mm, laying a substantial foundation for future applications.

The Gd₂O₂S:Tb scintillation ceramics is extensively used for neutron radiography and industrial non-destructive testing due to its bright green emission, high intrinsic conversion efficiency and high thermal neutron capture cross-section. However, the existence of Gd₂O₃ secondary phase in Gd₂O₂S ceramics impedes the scintillation property. In this work, The Gd₂O₂S:Tb precursors were synthesized in water-bath with H₂SO₄ and Gd₂O₃ as starting materials. Molar ratio of H₂SO₄ to Gd₂O₃ defined as n was adjusted to synthesize the precursors., which influence on the properties of the precursors and powders was studied. Chemical composition of the precursors changes with the increase of n, from 2Gd₂O₃·Gd₂(SO₄)₃·xH₂O (n<2.00) to Gd₂O₃·2Gd₂(SO₄)₃·xH₂O (2.25≤n≤2.75), and to Gd₂(SO₄)₃·8H₂O (n=3.00). After being calcined and reduced, all the powders form pure Gd₂O₂S phase. Morphology of the Gd₂O₂S:Tb powders is closely related to the phase composition of the precursor. Increasement of the XEL intensity shows two stages with n increase, corresponding to the phase transition of the precursor, respectively. The Gd₂O₂S:Tb scintillation ceramics were therefore fabricated by vacuum pre-sintering and HIP post-treatment. The ceramics were fabricated from the powders prepared with different n, achieving high relative density and XEL intensity, except the ceramics fabricated from the powders prepared with the n=2.00, 2.25, 2.50. The increase of n is beneficial to the removal of the Gd₂O₃ secondary phase from the Gd₂O₂S:Tb ceramics. This work provides a way for eliminating the secondary phase in Gd₂O₂S:Tb scintillation ceramics.

Neutron detection technology is widely used in homeland security, nuclear material security detection, and high energy physics, etc. Due to the shortage of ³He resources, it is urgent to develop a novel scintillator that can discriminate neutron and gamma. The Cs₂LaLiBr₆:Ce (CLLB:Ce) crystal has good neutron/gamma discrimination capacity, excellent energy resolution and high light yield, but its neutron/gamma discrimination performance needs further improvement. Here, the CLLB:Ce crystals co-doped with Zr⁴⁺ were grown successfully by the vertical Bridgman method. The results of different characterization methods prove that the Zr⁴⁺ was successfully doped into the matrix and did not effect on the structure of host. Meanwhile, no new luminescence center was generated after Zr⁴⁺ doping. The UV decay time is about 27 ns, presenting a fast fluorescence decay. Figure of merit (FOM) of CLLB:Ce crystal is enhanced from 1.2 to 1.5 by co-doping Zr⁴⁺, which means that the neutron/gamma discrimination performance of CLLB:Ce crystals is improved. Combined with the thermal stability and scintillation decay time, relationship between decay time and FOM was also analyzed. The co-doping of Zr⁴⁺ can inhibit shallow electron trap and V_K centers, reduce electron trapping-detrapping process, and greatly increase the probability of Ce³⁺ direct capturing electron, which results in a shorter decay time. Data from this study indicate that the CLLB:Ce crystals exhibit a huge application prospect in the field of neutron/gamma detection.

Dy³⁺-doped SrGdGa₃O₇ crystal was successfully grown through the Czochralski method and investigated in detail for its structural and optical features. Its crystallographic lattice parameters were optimized by Rietveld refinement based on XRD data. Polarized absorption spectra, polarized emission spectra, and fluorescence decay curves of Dy: SrGdGa₃O₇ crystal were analyzed. Absorption cross-sections at 452 nm corresponding to π- and σ-polarization were computed as 0.594×10^-21 and 0.555×10^-21 cm², respectively. Calculated effective J-O intensity parameters Ω₂, Ω₄, and Ω₆ were 5.495×10^-20, 1.476×10^-20, and 1.110×10^-20 cm², respectively. J-O analysis and emission spectra show that transition ⁴F_9/2→⁶H_13/2 of Dy: SrGdGa₃O₇ crystal has the highest fluorescence branching ratio and fluorescence intensity under 452 nm excitation within the visible spectral region, the emission cross-sections of π- and σ-polarization were 1.84×10^-21 and 2.49×10^-21 cm² at the wavelength of 574 nm, respectively. The measured radiative lifetime and fluorescence decay time of the Dy³⁺: ⁴F_9/2 level were 0.768 and 0.531 ms with a quantum efficiency of 69.1%. All these results reveal that Dy³⁺: SrGdGa₃O₇ crystal is a promising material for yellow lasers pumped with blue laser diodes.

Besides its application as nonlinear optical devices, La₂CaB₁₀O₁₉ (LCB) crystal has been extensively studied as a host crystal due to excellent properties. Nevertheless, rare-earth (RE) ions doped LCB crystals for ultraviolet (UV) lasers have not been studied yet. In this work, Ce³⁺ doped La₂CaB₁₀O₁₉ (Ce³⁺:LCB) crystal with the size of 40 mm×21 mm×6 mm was grown by top-seeded solution growth (TSSG) method. Its lattice parameters are slightly different from that of the LCB crystal, and its X-ray rocking curve indicates that the Ce³⁺:LCB is of high crystalline quality. Transmittance spectrum and UV absorption spectrum measured at room temperature show intense absorption in the ranges of 200-288 nm and 305-330 nm,and Sellmeier equations for the refractive indices were determined by least-squares method. The excitation and fluorescence spectra show that there are two broad excitation peaks at 280 nm and 316 nm, corresponding to transitions of Ce³⁺ ions from 4f to 5d. Four emission peaks were obtained at 290, 304, 331, and 355 nm, which correspond to transitions from 5d state to ²F_5/2 state and ²F_7/2 state. Ce³⁺:LCB crystal exhibits high thermal conductivity (6.45 W/(m·K)) at 300 K, and keeps good thermal stability with the increase of temperatures. Its thermal expansion coefficients and lattice parameters of c direction linearly enlarge from 2.94×10^-6 /K and 0.91240 nm to 5.3×10^-5 /K and 0.91246 nm in the temperature range from 358 K to 773 K, respectively. These results demonstrate that Ce³⁺:LCB crystal has excellent optical properties and good thermal stability, which is conducive to its application for UV lasers.