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Inorganic phosphors based on rare earth elements are commonly used as scintillation materials due to their high chemical and radiation resistance. In this work, we study gadolinium oxyselenide as a new phosphor material. The work describes a facile synthesis method for Gd 2 O 2 Se. Single crystal structure of this compound was determined for the first time: sp.gr. P ¯3 m 1 with a ​= ​3.8911(4) Å and c ​= ​6.8829(8) Å. Gd 2 O 2 Se is stable in the inert atmosphere and melts at 2075 ​± ​20 ​°C. This material is also stable when heated in air up to 720 ​°C. with the following oxidation and weight increase. This mass increase can be explained by the oxidation of Se2− to Se4+. Further temperature increase above 952°С leads to a sharp mass loss and the final mass of sample corresponds to full oxidation of Gd 2 O 2 Se to gadolinium oxide. The band gap of the material was estimated to be 3.6 ​eV. Photoluminescence spectrum for Gd 2 O 2 Se:Tb3+ shows the characteristic transitions in Tb3+ ion with the most intense green emission that corresponds 5D 4 → 7F J transitions. [Display omitted] • A powder of Gd 2 O 2 Se was obtained and the single crystal structure was determined: sp.gr. P ¯3 m 1, a ​= ​3.89Å, c ​= ​6.88 Å. • The melting point was found to be 2075 ​± ​20 ​°C. High air stability for this compound was demonstrated up to 720 ​°C. • The estimated value of the band gap is 3.6 ​eV. The photoluminescence of the Tb3+ doped sample was investigated. [ABSTRACT FROM AUTHOR]

• The optical constants of Lu 2 O 3 single crystals covering the UV–VIS–NIR spectral region are firstly investigated • The bandgap energy 5.541 ± 0.004 eV of Lu 2 O 3 single crystal is derived experimentally • Large-size and damage-free Lu 2 O 3 single crystal is obtained by chemical mechanical polishing Lu 2 O 3 has attracted widespread attention in high-power lasers, scintillators, and semiconductors due to its high thermal conductivity, high stability, and large band gap. Due to the limitations of the growth process, high-precision characterization of polished quality and optical properties for large-size Lu 2 O 3 single crystal is extremely scarce, which hinders the design and optimization of optics based on Lu 2 O 3. In this study, we design a systematic machining scheme for large-size Lu 2 O 3 single crystal thick chip to obtain polished crystal with virtually no surface and subsurface damage. The surface/subsurface quality was evaluated utilizing optical profilometer, scanning electron microscope, and transmission electron microscope. Variable-angle spectroscopic ellipsometer was employed to measure the optical constants over wide spectral region (210–1690 nm), removing the lack of optical constants of Lu 2 O 3 single crystal in the ultraviolet region. The band gap is analyzed based on the optical constants results. The consistency of the measured data with the relevant literature verifies the reliability and accuracy of the measurement method along with the data. The surface/subsurface damage inspection method provides an effective approach for ultra-precision machining mechanism research and process optimization of Lu 2 O 3 and other hard and brittle materials. The band gap and the optical constants in wide spectral region provide critical fundamental data for the design and performance optimization of related optics. [ABSTRACT FROM AUTHOR]