Optimizing the Structure and Optical Properties of Lanthanum Aluminate Perovskite through Nb5+ Doping

This work involves the introduction of niobium oxide into lanthanum aluminate (LaAlO3) via a conventional solid-state reaction technique to yield LaAlO3:Nb (LaNbxAl1-xO3+δ) samples with Nb5+ doping levels ranging from 0.00 to 0.25 mol%. This study presents a comprehensive investigation of the effects of niobium doping on the phase evolution, defect control, and reflectance of LaNbxAl1-xO3+δ powder. Powder X-ray diffraction (XRD) analysis confirms the perovskite structure in all powders, and XRD and transmission electron microscopy (TEM) reveal successful doping of Nb5+ into LaNbxAl1-xO3+δ. The surface morphology was analyzed by scanning electron microscopy (SEM), and the results show that increasing the doping concentration of niobium leads to fewer microstructural defects. Oxygen vacancy defects in different compositions are analyzed at 300 K, and as the doping level increases, a clear trend of defect reduction is observed. Notably, LaNbxAl1-xO3+δ with 0.15 mol% Nb5+ exhibits excellent reflectance properties, with a maximum infrared reflectance of 99.7%. This study shows that LaNbxAl1-xO3+δ powder materials have wide application potential in the field of high reflectivity coating materials due to their extremely low microstructural defects and oxygen vacancy defects.

Band Gap Engineering and Trap Depths of Intrinsic Point Defects in RAlO3 (R = Y, La, Gd, Yb, Lu) Perovskites

The possibility of band gap engineering (BGE) in RAlO₃ (R = Y, La, Gd, Yb, Lu) perovskites in the context of trap depths of intrinsic point defects was investigated comprehensively using experimental and theoretical approaches. The optical band gap of the materials, E _g, was determined via both the absorption measurements in the VUV spectral range and the spectra of recombination luminescence excitation by synchrotron radiation. The experimentally observed effect of E _g reduction from ∼8.5 to ∼5.5 eV in RAlO₃ perovskites with increasing R³⁺ ionic radius was confirmed by the DFT electronic structure calculations performed for RM^IIIO₃ crystals (R = Lu, Y, La; M^III = Al, Ga, In). The possibility of BGE was also proved by the analysis of thermally stimulated luminescence (TSL) measured above room temperature for the far-red emitting (Y/Gd/La)AlO₃:Mn⁴⁺ phosphors, which confirmed decreasing of the trap depths in the cation sequence Y → Gd → La. Calculations of the trap depths performed within the super cell approach for a number of intrinsic point defects and their complexes allowed recognizing specific trapping centers that can be responsible for the observed TSL. In particular, the electron traps of 1.33 and 1.43 eV (in YAlO₃) were considered to be formed by the energy level of oxygen vacancy (V_O) with different arrangement of neighboring Y_Al and V_Y, while shallower electron traps of 0.9-1.0 eV were related to the energy level of Y_Al antisite complexes with neighboring V_O or (V_O + V_Y). The effect of the lowering of electron trap depths in RAlO₃ was demonstrated for the V_O-related level of the (Y_Al + V_O + V_Y) complex defect for the particular case of La substituting Y.

Structure and luminescence behaviour of a novel red-emitting fluoroperovskite for display backlight application

In this work, we present a brand-new narrowband red-emitting fluoroperovskite via the introduction of Mn⁴⁺ into NaZnF₃ through a facile co-precipitation method at room temperature. The physicochemical properties of the fluoroperovskite such as crystal and electronic structures, morphology, and elemental composition, as well as its spectroscopic properties such as luminescence behaviours and optical performance were characterized and investigated in detail. Evidence shows that NaZnF₃:Mn⁴⁺ exhibits a uniform particulate shape with single-phase crystallinity. By virtue of the non-equivalent substitution and the [MnF₆] octahedral distortion in the fluoride host, sharp red emissions of phonon sidebands and the zero-phonon line upon blue light excitation are identified. Benefiting from the unique spectral feature, a wide colour gamut of 104.1% NTSC is achieved by coating β-SiAlON:Eu²⁺ and NaZnF₃:Mn⁴⁺ on an InGaN chip, indicating the potential use of the Mn⁴⁺ fluoroperovskite as a colour converter for display backlight application.