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:BaF 2 and 0.6 at.% Pr, 3 at.% Yb:BaF 2 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 Yb 3+ ions as a sensitizer of Pr 3+ ions, the broad near-infrared band emission from 1 G 4 energy level at 1.3 µm is observed in the Pr 3+ /Yb 3+ : BaF 2 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 1 G 4 → 3 H 5 and 3 P 0 → 3 H 4 transitions are calculated to be 0.21 × 10 −20 cm 2 and 1.12 × 10 −20 cm 2 with the larger FWHM of 103.8 nm and 4.2 nm in 0.6 at.% Pr, 3 at.% Yb:BaF 2 crystal, respectively. The luminescence lifetime of 1 G 4 and 3 P 0 energy levels are fitted to be 259.6 µs and 126.1 µs in 0.3 at.% Pr, 2.5 at.% Yb:BaF 2 crystal, which is much increased by Yb 3+ ions co-doping. The energy transfer efficiency in BaF 2 crystal from Yb 3+ to Pr 3+ ions is calculated to be 60.3% and 70.5%, respectively. All results show that the Pr 3+ /Yb 3+ :BaF 2 crystal is a promising candidate of laser gain medium for near-IR laser at 1.3 µm and blue laser operation.