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A series of high quality x%Pr3+:BaF2 (x = 0.6, 1, 2); (1%Pr3+, 2%Na+):BaF2; (1%Pr3+, y%Ca2+):BaF2 (y = 3, 5) and (0.6%Pr3+, 10%R3+):BaF2 (R = Y, Lu, Gd) crystals were grown by temperature gradient technique (TGT). The Raman spectra, absorption spectra, fluorescence spectra, and fluorescence decay lifetime were measured. XRD patterns indicate that the as-synthesized samples are pure BaF2 phase. The absorption cross-section of Pr3+ ions in the BaF2 matrix can be greatly improved by co-doping R3+ ions, while improvement by Na+ and Ca2+ ions is marginal. The fluorescence characteristic of Pr3+ ions can be effectively regulated by co-doping Na+, Ca2+, R3+ (R = Y, Lu, Gd) ions of different valence states. When R3+ ions are introduced, the fluorescence spectra show the strongest orange emission and the CIE chromaticity coordinates of Pr3+ ions are also in the orange region. When single-doped Pr3+ ions and Na+ or Ca2+ ions are introduced, the fluorescence lifetime of the 3P0 level is double exponential decay, and the short lifetime is the main proportion. However, the fluorescence centers tend to homogeneous and stable by R3+ ions co-doping and the fluorescence lifetime exhibits single-exponential decay, which is fitted to 49.7 μs, 47.8 μs and 49.6 μs of (0.6%Pr3+, 10%R3+):BaF2 (R = Y, Lu, Gd), respectively. All the results show that (Pr3+, Gd3+):BaF2 and (Pr3+, Na+):BaF2 are excellent laser gain media for high-efficiency orange and red laser operation. [ABSTRACT FROM AUTHOR]

High quality Dy3+: BaF 2 and Dy3+/RE3+ (RE = Tb, Eu): BaF 2 crystals were successfully grown by temperature gradient technology (TGT). The visible spectroscopic properties as well as the energy transfer mechanism of Dy3+ and Tb3+/Eu3+ co-doped BaF 2 crystals were systematically discussed. The spectral performance at 575 nm (Dy3+: 4F 9/2 → 6H 13/2) emission was significantly improved by co-doping Tb3+/Eu3+ ions. Through the upper level lifetime changed, it can be proved that there is a quasi resonance energy transfer between Dy3+: 6H 13/2 and Tb3+: 7F 4 / Eu3+: 7F 4 states, and the final gain effect exceeds negative influence of the upper level energy transfer. Meanwhile, the optimal concentration ratio of Dy3+/Tb3+ and Dy3+/Eu3+ in double-doped crystals was relatively different. The optimal ratio of Dy3+/Tb3+ was 10:1 in 2%Dy3+,0.2%Tb3+: BaF 2 crystal. The emission cross section increases from 8.147 × 10−22 cm2 to 11.284 × 10−22 cm2 with an increase of 38.5 %, and the quality factor (σ em ⋅τ) increases by 22.3 %. The optimal ratio of Dy3+/Eu3+ was 20:1 in 2%Dy3+,0.1%Eu3+: BaF 2 crystal, the emission cross section is increased to 10.411 × 10−22 cm2 with an increase of 27.8 %, and the quality factor increases by 26.9 %. The above results show that Dy3+: BaF 2 crystals co-doped with deactivated ions (Tb3+/Eu3+) of low concentration have great potential as gain media for yellow laser output. • High quality Dy3+:BaF 2 and Dy3+/Re3+(Re Tb, Eu):BaF 2 crystals were grown by TGT, and various performance was measured. • Various spectral performance of Dy3+:BaF 2 has been improved by Tb3+/Eu3+ doped, and the maximum increase is up to 38.5 %. • These results show that Dy3+/Re3+(Re Tb, Eu):BaF 2 crystals have great potential as yellow laser medium. [ABSTRACT FROM AUTHOR]

• A promising laser gain medium at 2.7 μm region, 7 at.% Er:Y 2 O 3 single crystal has been successfully grown. • The mid-infrared continuous-wave laser properties of 7 at.% Er:Y 2 O 3 crystal have been demonstrated for the first time. • By using saturable absorber, the pulsed laser at 2724 nm with the shortest pulse duration of 393 ns was achieved. As a promising laser gain medium at 2.7 μm region, 7 at.% Er:Y 2 O 3 single crystal has been successfully grown, but its laser properties have not yet been reported. Using Er:Y 2 O 3 crystals as laser gain medium means that the problem of optical diffraction loss in Er:Y 2 O 3 ceramics was avoided and higher quality laser can be obtained. On this basis, the continuous wave and passively Q-switched laser properties of this crystal have been demonstrated for the first time in this work. In continuous-wave operation, the maximum output power of 220 mW was obtained at 2725 nm. In the passively Q-switched operation, a 2724 nm laser was achieved with a shortest pulse duration of 393 ns. This is the first laser demonstration of the 7 at.% Er:Y 2 O 3 cubic crystal, and also is a vital step towards obtaining a higher quality mid-infrared laser. These laser characteristics also indicate great potential of Er:Y 2 O 3 crystal for the generation of mid-infrared lasers. [ABSTRACT FROM AUTHOR]

• A series of 0.6 at% Pr:CaF 2 -RF 3 (R= Y3+, Gd3+, Lu3+) crystals were successfully grown by the temperature gradient technique(TGT) method. • By co-doping R3+ ion (R=Y3+, Gd3+, Lu3+), the spectral performance of the crystals could be significantly improved and the function effect is also different. • The spectral performance and spectral quality factor of the crystals were systematically described and compared for the first time. • The spectral modulation effect caused by Y3+, Gd3+ and Lu3+ co-doping ion was discussed. A series of 0.6 at% Pr:CaF 2 -RF 3 (R = Y3+, Gd3+, Lu3+) crystals have been successfully grown by the temperature gradient technique(TGT). The absorption spectra, fluorescence spectra, and fluorescence decay curves were measured and analyzed at room temperature. When the R3+ concentration is higher than a certain value, the diffraction peaks of Pr:CaF 2 -RF 3 crystals were well indexed to the (Ca,Y)F 2 phase. By co-doping R3+ ion (R=Y3+, Gd3+, Lu3+), the spectral performance of the crystals could be significantly improved and the function effect is also different. For 0.6 at% Pr, 28.5 at% Y:CaF 2 crystal, the fluorescence lifetime of 3P 0 energy level was fitted to be 45.46 µs, and the emission cross sections of 3P 0 →3H 6 (605 nm), and 3P 0 →3F 2 (641 nm) were calculated to be 1.78 × 10−20 cm2, and 4.61 × 10−20 cm2 with the full width at half (FWHM) of 20.1 nm and 6.8 nm, respectively. The 0.6 at% Pr, 28.5 at% Y:CaF 2 crystal could be favorble laser medium for ultra-fast laser opreration at 605 nm and 641 nm. For 0.6 at% Pr, 18 at% Gd:CaF 2 and 0.6 at% Pr, 10 at% Lu:CaF 2 crystals, the spectral quality factors σ em• τ f of 3P 0 →3F 2 transition (642 nm) were calculated to be 614.18 × 10−20 cm2•µs and 506.36 × 10−20 cm2•µs with the FWHM of 3.7 nm and 5.3 nm. All the results show that 0.6 at% Pr, 18 at% Gd:CaF 2 and 0.6 at% Pr, 10 at% Lu:CaF 2 crystals are promising gain media for high-efficiency visible laser output at 642 nm, which would compete with commercial Pr: YLF crystal in the future. [ABSTRACT FROM AUTHOR]

Yb,Pr:CaF 2 crystals have been grown successfully by the temperature gradient technique(TGT). The absorption spectra, fluorescence spectra, fluorescence decay lifetime of Pr3+ ions in CaF 2 crystal sensitized by different Yb3+ ions concentration have been measured. The effective J-O intensity parameters were fitted to be Ω 2 =0.36 × 10−20cm2, Ω 4 =2.89 × 10−20cm2, Ω 6 =6.69 × 10−20cm2 for 0.3 at.%Pr,1.5 at.%Yb:CaF 2. And the emission cross sections of 3P 1 →3H 5 (535 nm), and 3P 0 →3F 4 (750 nm) are calculated to be 2.02 × 10−20cm2, and 2.50 × 10−20cm2 with the FWHM of 17.2 nm, and 10.5 nm, respectively. The fluorescence lifetime of 3P 0 has achieved great increasing by sensitizing of Yb3+ ion. Not only the up-conversion luminescence can be achieved, but also the broad band emission from 1D 2 energy level can be observed. The results show that Yb,Pr:CaF 2 could be a potential laser gain medium for visible and near-IR laser operation. • Not only the up-conversion luminescence can be achieved, but also the broad band emission from 1D 2 energy level can be observed by Yb3+ ion sensitizing. • Spectral properties and Judd-Ofelt parameters of Yb,Pr:CaF 2 crystal were investigated and analysed. [ABSTRACT FROM AUTHOR]