Luminescence Properties of an Orthorhombic KLaF4 Phosphor Doped with Pr3+ Ions under Vacuum Ultraviolet and Visible Excitation

Fluorides have a wide bandgap and therefore, when doped with the appropriate ions, exhibit emissions in the ultraviolet C (UVC) region. Some of them can emit two photons in the visible region for one excitation photon, having a quantum efficiency greater than 100%. In a novel exploration, praseodymium (Pr3+) ions were introduced into KLaF4 crystals for the first time. The samples were obtained according to a high-temperature solid-state reaction. They exhibited an orthorhombic crystal structure, which has not been observed for this lattice yet. The optical properties of the material were investigated in the ultraviolet (UV) and visible ranges. The spectroscopic results were used to analyze the Pr3+ electronic-level structure, including the 4f5d configuration. It has been found that KLaF4:Pr3+ crystals exhibit intense luminescence in the UVC range, corresponding to multiple 4f → 4f transitions. Additionally, under vacuum ultraviolet (VUV) excitation, distinct transitions, specifically 1S0 → 1I6 and 3P0 → 3H4, were observed, which signifies the occurrence of photon cascade emission (PCE). The thermal behavior of the luminescence and the thermometric performance of the material were also analyzed. This study not only sheds light on the optical behavior of Pr3+ ions within a KLaF4 lattice but also highlights its potential for efficient photon management and quantum-based technologies.