Photoluminescence Characteristics and Judd–Ofelt Analysis of Yba3(Bo3)3:Tb3+ Phosphors Co-Doped with Li+, Na+, and K+: Insights from Structural and Lifetime Studies

Abstract

This study presents a systematic investigation of the photoluminescent properties of Tb3+-doped YBa3(BO3)3 (YBBO) phosphors, synthesized via a microwave-assisted sol-gel combustion (MA-SG) method and co-doped with monovalent alkali ions (Li+, Na+, K+). Structural, vibrational, and morphological analyses were performed using XRD with Rietveld refinement, Raman and FTIR spectroscopy, and SEM–EDS. These analyses confirmed the successful incorporation of dopants without compromising the borate lattice. Photoluminescence (PL) measurements under near-UV excitation (377 nm) showed intense green emission attributed to the 5D4 → 7F5 transition of Tb3+, with Li+ co-doping producing the greatest enhancement (~2.7×) in emission intensity. Lifetime measurements revealed longer decay times with co-doping, suggesting reduced non-radiative relaxation processes. Judd–Ofelt (J–O) analysis confirmed strong radiative transitions and high internal quantum efficiency (η ≈ 48.4%). Colorimetric analysis using CIE chromaticity diagrams validated the tunable green emission behaviour of the phosphors. Minor deviations from ideal green were linked to background blue emission from the host matrix, a feature that may offer spectral advantages in multifunctional optical applications. These results highlight the crucial role of alkali ion co-doping in tuning the local crystal field, enhancing emission efficiency, and paving the way for the development of efficient green-emitting phosphors for solid-state lighting applications.

Keywords: YBa3(BO3)3 phosphors, Tb3+ doping, Photoluminescence, Judd-Ofelt analysis, lifetime measurements