The terbium-activated yttrium tantalite ($\mathrm{YTa}{\mathrm{O}}_4\text{:}{\mathrm{Tb}}^{3+}$) phosphor is of great interest due to the interesting spectroscopic properties of rare earth ions in crystals and also practical use in x-ray imaging. Using the group-theoretical approach, we analyze the selection rules for the transition between Stark components of ${\mathrm{Tb}}^{3+}$ in symmetry of the actual crystal field and the polarization for the allowed transitions. The luminescence upon UV, vacuum-ultraviolet (VUV), and x-ray excitation is presented and discussed. The $\mathrm{YTa}{\mathrm{O}}_4\text{:}{\mathrm{Tb}}^{3+}$ phosphors are found to be efficient VUV-excited luminescent materials that could be used not only in x-ray intensifying screens, but also in mercury-free fluorescent lamps or plasma display panels.

Rare earth activated Y TaO4 based phosphors are perspective materials for optoelectronics. The paper presents some physical and chemical aspects related to the influence of the host lattice composition and crystalline order on the luminescence of rare earth ions. In this respect, Eu-activated Y (Ta,Nb)O4 powders have been prepared by solid state reaction, from homogeneous mixtures consisting of oxide precursors and flux. Photoluminescence (PL) spectroscopy, X-ray diffraction, FTIR spectroscopy and SEM have been used to investigate the structural and luminescent properties of Y (Ta,Nb)O4:Eu phosphors. Attempts has been made at establishing a correlation between the morphostructural parameters of the host lattice containing variable niobium amount and the PL properties. The interaction between the tantalate-niobate matrix and the Eu-emission centres is considered in correlation with the PL characteristics

In this article, the study of the influence of the calcination temperature on the crystallographic, compositional, and morphological properties of the natural hydroxyapatite taken from sheep bones was carried out. The obtained samples were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy, with elemental analysis (SEM-EDS) in order to obtain structural information, compositional and morphological properties. In the thermogravimetric curves, the decomposition temperatures of the organic phases present in the sheep bones powder were identified. In the X-ray diffraction analyzes, it was found that the diffraction patterns presented characteristic peaks of hydroxyapatite and, it was observed that the increase in temperature favors the growth crystallite size. Likewise, in the morphological analysis, changes in the samples were verified, finding greater agglomeration of the particles, while the EDS analyzes revealed the different Ca/P relationships for the calcination temperatures used. In the FTIR spectra, the characteristic vibrational bands of the phosphate and hydroxyl functional groups present in the samples were observed. Moreover, due to the temperature changes, the vibrational bands corresponding to water and proteins disappeared, and a decrease in the carbonate bands was also identified.

In this work, we investigate the influence of M substitutions (M = P, Bi, and Sb) on the structural, electronic, and optical properties of gallium arsenide, GaM _x As_1-x for x = 0 , 0.25 , 0.50 , 0.75 , 1.0 using density functional theory (DFT). We have observed that the cubic symmetry of the semiconductors in conserved, and lattice constants show a linear behavior with dopant concentration, according to Vegard’s law. Specifically, the lattice constants increased for Bi and Sb dopants, whilst decreased for P dopants. Furthermore, the bulk modulus decreased with an increase in M-concentration for all M-doped systems. The energy analysis showed that the P-doped system was the most stable system. In terms of the electronic band structure, all M-doped compounds exhibited a direct electronic band gap. The P-doped system showed a wide band gap, while the Sb-doped systems displayed a narrow band gap, both compared to pristine GaAs. The Bi-doped system showed metallic-like behavior. To gain insights into the linear optical properties of the GaM _x As_1-x compounds, we calculated the real and imaginary parts of the dielectric function, as well as other optical parameters such as the absorption coefficient, refractive index, extinction coefficient, and reflectivity. The results showed that P doping leads to a blue-shift in the optical absorption coefficient, while Bi and Sb doping lead to a red-shift. These findings provide valuable theoretical insights for the potential application of GaM _x As_1-x semiconductors in photovoltaics and optoelectronic devices.