Synthesis and Upconversion Luminescence of LiY₉(SiO₄)₆O₂ Phosphor Doped with Pr³⁺

The increasing demand for ultraviolet light sources in various industries, including security, phototherapy, and sterilization, has spurred research efforts toward discovering new UV phosphors. Herein, we introduce LiY9(SiO4)6O2:Pr3+ as a novel ultraviolet-C (UVC) phosphor, synthesized via the sol–gel technique with varying Pr3+ concentrations (0, 0.1, 0.5, 1, 1.5, and 2%). For the first time, this study comprehensively describes the emission and excitation spectra, as well as the emission decay kinetics of Pr3+ ions in LiY9(SiO4)6O2. Two distinct classes of Pr3+-emitting centers were identified, denoted as Pr(1) and Pr(2), which replace Y ions at two different lattice sites, 4f and 6h, respectively. Pr3+ ions at the 4f site exhibit 4f2 → 4f2 emission solely, while those at the 6h site emit predominantly in the ultraviolet, 75% of which is in the UVC range. Furthermore, LiY9(SiO4)6O2:Pr3+excited by laser at a wavelength of 444 nm, both a continuous wave and a pulse, exhibits upconversion emission in the UV region. Upconversion mechanisms were analyzed regarding Pr3+ concentrations and the excitation regime. Upconversion was found to result from the excited-state absorption. However, for the pulse excitation, a very small fraction of Pr3+ ions is excited to 4f15d1 levels involving the energy transfer upconversion mechanism.