A Comparative Investigation of the Photoluminescence Properties and Thermal Stability of Rare-Earth Doped MMeR(BO₃)₂ and KCaR(BO₃)₂ Borate Phosphors

This chapter presents a systematic study of the optical properties and photoluminescence behavior of rare-earth (RE³⁺ = Eu³⁺, Tb³⁺, Dy³⁺) activated MMeR(BO₃)₂ and KCaR(BO₃)₂ borate phosphors. The analysis encompasses electronic transitions, excitation/emission characteristics, concentration-dependent quenching, decay lifetime dynamics, thermal stability, and Judd-Ofelt theory. The dominant emission features include the red emission of Eu³⁺ (⁵D₀ → ⁷F₂ at ~614 nm), green emission of Tb³⁺ (⁵D₄ → ⁷F₅ at 545 nm), and yellow/blue emissions of Dy³⁺ (⁴F₉/₂ → ⁶H₁₃/₂,₁₅/₂). A prominent O²⁻→Eu³⁺ charge-transfer band is observed in the UV region, with its position and width being host-dependent. Judd-Ofelt intensity parameters (Ω₂, Ω₄, Ω₆) quantify the local site asymmetry and covalency, revealing MMeBO₃ as a host with higher asymmetry. Thermal quenching analysis demonstrates that Tb³⁺-doped samples exhibit superior thermal stability with the highest activation energy (0.158 eV), while Dy³⁺-doped systems are more susceptible to thermal degradation. The results establish these borate hosts as promising candidates for solid-state lighting and display applications.