Enhanced emission of 2.9 μm from Ho3+/Pr3+ co-doped LiYF4 crystal excited by 640 nm

The use of Pr 3+ co-doping for great enhancement of mid-infrared (mid-IR) emissions at 2.9 μm and 2.4 μm is investigated in the Ho 3+ /Pr 3+ co-doped LiYF 4 crystals. With the introduction of Pr 3+ ions, the fluorescence lifetime of Ho 3+ : 5 I 7 level is 2.15 ms for Ho 3+ /Pr 3+ co-doped crystal, and the lifetime for Ho 3+ singly doped crystal is 17.70 ms, while the lifetime of Ho 3+ : 5 I 6 level decreases slightly from 2.11 ms for Ho 3+ :LiYF 4 to 1.83 ms for Ho 3+ /Pr 3+ :LiYF 4 . It is also demonstrated that the introduction of Pr 3+ greatly increases the mid-infrared emission of Ho 3+ : 5 I 6 → 5 I 7 which depopulates the Ho 3+ : 5 I 7 level, while it has little influence on the Ho 3+ : 5 I 6 level, which is beneficial for greater population inversion and laser operation. The analysis on the decay curves of the 2.0 μm emissions in the framework of the Inokuti-Hirayama model indicates that the energy transfer from Ho 3+ to Pr 3+ is mainly from electric dipole-dipole interaction. The calculated efficiency of energy transfer from Ho 3+ : 5 I 7 to Pr 3+ : 3 F 2 level is 87.53% for Ho 3+ /Pr 3+ (1.02%/0.22%) co-doped sample. Our results suggest that the Ho 3+ /Pr 3+ co-doped LiYF 4 single crystals may have potential applications in mid-IR lasers.