Vacuum ultraviolet spectroscopic properties of Pr3+ in MYF4 (M=Li, Na, and K) and LiLuF4

LiYF4, NaYF4, KYF4 and LiLuF4 doped with Pr3+ were synthesized by hydrothermal technique. Vacuum ultraviolet excitation and emission properties were investigated at 20 K. A new type of photon cascade emission was observed in LiYF4:Pr3+ and LiLuF4:Pr3+, i.e. a first-step 4f5d→4f2 emission followed by a second 4f2→4f2 emission. In addition, the internal quantum efficiency of Pr3+ in NaYF4 and KYF4 within visible range was proved to be larger than unity using the branching ratios data corrected by the emission spectra of YF3:Pr3+.