Synthesis, structural characterization, and photoluminescence behavior of NaCa4(BO3)3:Tb3+ phosphors Co-doped with K+: Insights into radiation-induced defect formation and charge compensation via DFT calculations

Abstract

This study explores the structural, optical, and electronic properties of NaCa₄(BO₃)₃:Tb³⁺ phosphors, with and without K⁺ co-doping, via experimental techniques and Density Functional Theory (DFT). X-ray diffraction confirmed Tb³⁺ and K⁺ incorporation without phase change. Optimal green photoluminescence at 542 nm occurred at 2 wt% Tb³⁺; higher doping led to quenching due to multipolar interactions. While Tb³⁺ enhanced luminescence, K⁺ co-doping reduced it, likely from charge imbalance and defect formation. DFT results aligned with experiments, showing minor lattice distortion from Tb³⁺ and structural instability from K⁺, reflected in a slight band gap reduction (from 5.00 eV to 4.97 eV). Bader charge and formation energy analyses confirmed K⁺ does not fully compensate for charge imbalance, contributing to non-radiative centers and reduced luminescence. CIE analysis indicated tunable emission between green and yellow-green. These findings reveal K⁺ impacts beyond charge compensation, offering insights for phosphor design in solid-state lighting.