Yb3+ sensitization effect to Pr3+ originated from 1G4 level broadband near-infrared emission and up-conversion in BaF2 crystal

High quality 0.3 at.% Pr, 2.5 at.% Yb:BaF2 and 0.6 at.% Pr, 3 at.% Yb:BaF2 single crystals were grown by the temperature gradient technique (TGT). The absorption spectra, fluorescence spectra, fluorescence decay curves and energy transfer process are measured and analyzed at room temperature. By co-doping Yb3+ ions as a sensitizer of Pr3+ ions, the broad near-infrared band emission from 1G4 energy level at 1.3 µm is observed in the Pr3+/Yb3+: BaF2 crystal with low maximum phonon energy for the first time. In addition, the visible fluorescence emission can be detected and the luminescence components are mainly blue-green transition. The emission cross sections of 1G4→3H5 and 3P0→3H4 transitions are calculated to be 0.21 × 10−20 cm2 and 1.12 × 10−20 cm2 with the larger FWHM of 103.8 nm and 4.2 nm in 0.6 at.% Pr, 3 at.% Yb:BaF2 crystal, respectively. The luminescence lifetime of 1G4 and 3P0 energy levels are fitted to be 259.6 µs and 126.1 µs in 0.3 at.% Pr, 2.5 at.% Yb:BaF2 crystal, which is much increased by Yb3+ ions co-doping. The energy transfer efficiency in BaF2 crystal from Yb3+ to Pr3+ ions is calculated to be 60.3% and 70.5%, respectively. All results show that the Pr3+/Yb3+:BaF2 crystal is a promising candidate of laser gain medium for near-IR laser at 1.3 µm and blue laser operation.