Research on the properties and LD-pumped CW laser emission at 2.7 µm in Er3+:KLu(WO4)2 and Er3+/Pr3+:KLu(WO4)2 crystals

Two laser crystals of Er3+:KLu(WO4)2 and Er3+/Pr3+:KLu(WO4)2 were successfully grown using the top-seeded solution growth technique with K2W2O7 as flux. Segregation coefficients of Er3+ ions in Er3+:KLu(WO4)2 and Er3+/Pr3+:KLu(WO4)2 crystals were 0.664 and 0.9, respectively. The density of the Pr3+ ions in the Er3+/Pr3+:KLu(WO4)2 crystal was 1.19 × 1019 cm−3, and the segregation coefficient was 0.18. The absorption and fluorescence spectra of the two crystals with Y-oriented polarization (parallel to the b axis) light were recorded. Judd–Ofelt (J–O) theory was adapted to analyze the main parameters and they were crucial for evaluating the potential of laser crystals with output wavelength of 2.7 µm. Results showed that the Er3+/Pr3+:KLu(WO4)2 crystal had good J–O intensity parameter Ωt (t = 2, 4, 6) and relatively large emission cross section at 2.7 µm. The lifetimes of the 4I11/2 state in the Er3+:KLu(WO4)2 and Er3+/Pr3+:KLu(WO4)2 crystals were fitted to be 87.13 ms and 79.36 ms, respectively. The lifetime of 4I13/2 state decreased sharply from 5.59 s in Er3+:KLu(WO4)2 to 53.19 ms with co-doping of Er3+ ions and Pr3+ ions. Laser oscillation was accomplished at 2.7 µm wavelength using a b-cut Er3+/Pr3+:KLu(WO4)2 crystal sample with size of 4 × 4 × 10 mm3. Finally, a continuous-wave (CW) laser was realized with the highest slope of 15.94%. The center wavelength of the laser output was 2740 nm, and its FWHM was approximately 1.8 nm. Therefore, the Er3+/Pr3+:KLu(WO4)2 crystal has remarkable potential for generating 2.7 µm lasers.