Phosphor-converted white light-emitting diodes (pc-WLEDs) are promising materials for next-generation lighting technologies. For luminescence to occur in a phosphor, an activator and a host lattice are needed. Here, the typical inorganic phosphor REx:NBT consists of activator ions (Eu3+, Gd3+, and Dy3+) incorporated into a host matrix (NBT) with different concentrations. Generally, RE3+ ions prefer to occupy Bi-sites in NBT. But, some concentrations of REx:NBT show amphotericity (i.e., dopant chooses more than one site for its substitution). The amphoteric behavior of Eu, Gd, and Dy in NBT is confirmed by Judd-Ofelt analysis, Raman spectral studies, and neutron diffraction results, respectively.

Further more, a new tolerance factor (tR) is derived to study the stability and doping effects of RE ions in rhombohedral ABO3 structures. Generally, amphotericity induces crystal volume changes and results strain (ε) in the material. Therefore, hydrostatic strain-induced ab-initio electronic structure (ε = -0.02 (compressive) to 0.02 (tensile) in steps of 0.01) calculations are done in NBT using density-functional theory. All the above-discussed structural, optical, and electronic properties of ABO3 perovskites are dependent on the crystal structure they adopt.
Given the above, a priori prediction of crystal structure classification of ABO3 perovskites is desirable. Hence in this work, crystal structure classification of ABO3 perovskites is done using Light Gradient Boosting Machine (Light GBM) algorithm. It successfully categorized perovskites into cubic, tetragonal, orthorhombic, and rhombohedral structures with 80.3% best accuracy using 5-fold cross-validation.