Luminescence Properties of an Orthorhombic KLaF 4 Phosphor Doped with Pr 3+ 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 (Pr 3+ ) ions were introduced into KLaF 4 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 Pr 3+ electronic-level structure, including the 4 f 5 d configuration. It has been found that KLaF 4 :Pr 3+ crystals exhibit intense luminescence in the UVC range, corresponding to multiple 4 f → 4 f transitions. Additionally, under vacuum ultraviolet (VUV) excitation, distinct transitions, specifically 1 S 0 → 1 I 6 and 3 P 0 → 3 H 4 , 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 Pr 3+ ions within a KLaF 4 lattice but also highlights its potential for efficient photon management and quantum-based technologies.