Broadband transparent films play a pivotal role in various applications such as lenses and solar cells, particularly porous structured transparent films exhibit significant potential. This study investigates a porous SiO₂ refractive index gradient anti-reflective film prepared by atomic layer deposition (ALD). A porous SiO₂ film with gradual porosity was obtained by phosphoric acid etching of Al₂O₃/SiO₂ multilayers with gradient Al₂O₃ ratios, achieving a gradual decrease in refractive index from the substrate to the surface. The film exhibited an average transmittance as high as 97.8% within the wavelength range from 320 nm to 1200 nm. The environmental adaptability was further enhanced by surface modification using rare earth oxide (REO) La₂O₃, resulting in formation of a lotus leaf-like structure and achieving a water contact angle of 100.0°. These data proved that the modification significantly improved hydrophobic self-cleaning capability while maintaining exceptional transparency of the film. The surface structure of the modified film remained undamaged even after undergoing wipe testing, demonstrating its excellent surface durability.

Y₃Al₂Ga₃O₁₂:Ce³⁺,Cr³⁺ (YAGG:Ce³⁺,Cr³⁺), as a persistent luminescent material, has advantages of high initial luminescence intensity and long persistent time, which is promising in persistent luminescent material applications. At present, YAGG:Ce³⁺,Cr³⁺ powders exhibit good persistent performance, but their persistent performance of ceramics still needs to be further improved to meet the new requirements. In this work, (Y_0.998Ce_0.002)₃(Al_1-xCr_x)₂Ga₃O₁₂ ceramics with different Cr³⁺ doping concentrations were prepared by solid-state reaction, including air pre-sintering, hot isostatic pressing (HIP) post-treatment and air annealing, to investigate the effects of Cr³⁺ doping concentration on the microstructure, optical properties and persistent performance of the ceramics. The results showed that as the doping concentration of Cr³⁺ increased from 0.025% to 0.2% (in atom), no significant effect of Cr³⁺ concentration on the morphology of pre-sintered ceramics or HIP post-treatment ceramics was observed, but the in-line transmittance gradually increased while the persistent performance gradually decreased. Among them, YAGG:Ce³⁺,Cr³⁺ ceramics doped with 0.025% Cr³⁺ showed the strongest initial luminescence intensity exceeding 6055 mcd/m² and a persistent time of 1030 min after air pre-sintering combined with HIP post-treatment and air annealing. By optimizing the Cr³⁺ doping concentration and the fabrication process, the persistent luminescence (PersL) performance of the YAGG:Ce³⁺,Cr³⁺ ceramics was obviously improved.

In the field of optoelectronic devices, p-type transparent semiconductor materials with controllable electrical properties hold significant application value. CuI, as a representative material, still faces considerable technical challenges in terms of preparation processes and doping control. This study successfully developed a new p-type transparent semiconductor material with adjustable electrical properties through manganese cation doping, offering a new approach for the advancement of transparent electronics. The Cu_1-xMn_xI solid solution film, prepared via reactive magnetron sputtering, exhibits unique performance advantages. Firstly, the material can be fabricated at room temperature while maintaining excellent visible light transparency. Secondly, as the manganese doping concentration (x) increases, the grain size of the film gradually decreases, and pronounced crystal cluster aggregation is observed at higher doping concentrations. X-ray photoelectron spectroscopy analysis reveals that manganese ions in the film exist in a mixed valence state of Mn²⁺ and Mn³⁺. Electrical performance characterization shows that the resistivity of the film can be tuned over two orders of magnitude, ranging from 0.017 to 2.5 Ω·cm, while the hole carrier concentration remains stable at a high order of magnitude of 10¹⁸-10¹⁹ cm^-3. Unlike the n-type doping behavior observed in traditional semiconductors, introduction of high-valent manganese ions does not significantly affect the p-type conductivity of the material. This is likely due to the partially localized electronic state formed when manganese replaces cuprous ions. This discovery suggests that the hole conductivity of CuI semiconductors is not easily affected by high-valent manganese ion doping, enabling a wide range of compositional adjustments while maintaining stable p-type conductivity. This study provides a valuable material basis for the development of CuI-based multifunctional transparent electronic devices.

Lithium niobate (LiNbO₃, LN) is an artificial crystal with excellent physical properties, such as acousto-optic, electro-optic, piezoelectric, and photorefractive performance. It is not only seen as "optical silicon", but also suggests that humans are entering the era of "Lithium Niobate Valley". Its excellent optoelectronic properties have a wide potential application in emerging fields, such as artificial intelligence and photoelectric hybrid module. Photorefraction was found and proved to be an important property of LN crystal. With development of optoelectronic devices based on LN to micro- and nano-scale, photorefractive effect has gradually appeared. Single crystal LN is the basic material for preparing various devices taking advantage of lithium niobate on insulator (LNOI). The photorefractive properties can be adjusted by doping appropriate impurity ions. Compared with normal ions (valence < +5 (valence of niobium ions)), incorporation of high-valence ions (valence ≥ +5) can be more beneficial to improve photorefractive performances of LN crystals in recent years. This paper summarizes research progress of high-valence ion-doped LN crystals of which doping with V, Mo, U, and Bi ions can effectively adjust their photorefractive properties, suitable for designing micro-ring resonators, optically programmable photonic components, nonlinear photonic devices, and other micro- and nano-scale devices. Finally, based on above advances in high-valence ion doped LN, further research may achieve unprecedented improvements in four aspects: high-quality and big-size crystal growth, photorefractive mechanism, ion doping with lone-pair electrons, and novel optoelectronic devices.

Diamond with excellent properties and broad application prospects in the fields of thermal management of optics and electronic devices, and wide bandgap semiconductors, is known as the ultimate semiconductor. As an optical window, a large-sized CVD (chemical vapor deposition) diamond free-standing thick film with a thickness of ≥2 mm is required. In semiconductor heat dissipation, a diamond free-standing film with a diameter over 4 inches (1 inch=2.54 cm) and a thickness of 100 μm is required to bond with semiconductor materials such as gallium nitride (GaN). However, there still exist significant difficulties in synthesis and application of large-area CVD diamond films. On the one hand, stress during the deposition process can cause the diamond film to rupture. On the other hand, residual stress can cause the diamond film to warp, resulting in poor bonding quality. Therefore, controlling the stress of diamond films has become a key issue for the large-scale and widespread application of diamond films. This article summarizes the classification, sources, and influencing factors of CVD diamond stress, and provides a detailed introduction to measures for suppressing stress in diamond films. Furthermore, researches on improving diamond properties by artificially applying stress are summarized, including changing diamond bandgap and increasing diamond thermal conductivity under stress. Finally, a method and theoretical calculation formula for evaluating the stress magnitude of diamond are provided, and the future trend of stress research on diamond films is analyzed.

Sc₂O₃, as a host for solid-state laser gain materials, has advantage of high thermal conductivity and easy matching with activating ions, which is promising in high-power laser applications. Currently, Yb-doped Sc₂O₃ ceramics have been fabricated at very high sintering temperatures, but their optical quality and sintering process still need further improvement. In this work, 5%Yb:Sc₂O₃ (in mass) nano-powders were obtained by co-precipitation, and then transparent ceramics were fabricated by vacuum pre-sintering and hot isostatic pressing (HIP) post-treatment. The cubic Yb:Sc₂O₃ nano-powders with good dispersity and an average crystallite of 29 nm were obtained. Influence of pre-sintering temperatures (1500-1700 ℃) on densification process, microstructure changes, and optical transmittance of Yb:Sc₂O₃ ceramics was detected. Experimental data revealed that all samples have a uniform microstructure, while the average grain sizes increase with the increase of the sintering temperatures. Impressively, the optimum in-line transmittance of Yb:Sc₂O₃ ceramics, pre-sintered at 1550 ℃ after HIP post-treatment, reaches 78.1% (theoretical value of 80%) at 1100 nm. Spectroscopic properties of the Yb:Sc₂O₃ ceramics reveal that the minimum population inversion parameter β₂ and the luminescence decay time of 5%Yb:Sc₂O₃ ceramics are 0.041 and 0.49 ms, respectively, which demonstrate that the optical quality of the Yb:Sc₂O₃ has been improved. Meanwhile, their best vacuum sintering temperature can be controlled down to a lower temperature (1550 ℃). In conclusion, Yb:Sc₂O₃ nano-powders are successfully synthesized by co-precipitation method, and good optical quality transparent ceramics are fabricated by vacuum pre-sintering at 1550 ℃and HIP post-treatment.

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.

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.