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A new Cr 3+ , Yb 3+ , Ho 3+ , and Pr 3+ co-doped GYSGG (Gd 2 YSc 2 Ga 3 O 12 ) single crystal with a size of Φ 26 mm × 80 mm was grown successfully using the Czochralski method for the first time. Absorption spectrum is studied, and main absorption bands are centered at 449, 638, and 934 nm. The fluorescence spectrum shows a broad emission band around 2.8 µm, indicating the Cr 3+ and Yb 3+ ions can act as the sensitizer for the Ho 3+ ions. The fluorescence lifetimes of the 5 I 6 and 5 I 7 levels of the Ho 3+ ions are fitted to be 0.39 and 5.31 ms, respectively. By comparison with those of the Cr,Yb,Ho:GYSGG crystal, the Pr 3+ ions acting as the deactivator can decrease efficiently the lifetime of the lower laser level 5 I 7 of the Ho 3+ ions. Additionally, a flash lamp pumping 2.84 µm laser with maximum average power of 257 mW is achieved. These results indicate the Cr,Yb,Ho,Pr:GYSGG crystal is a new promising radiation-resistant laser gain medium applied in radiant environment. [ABSTRACT FROM AUTHOR]

A novel Yb,Ho,Pr:LuYAG laser crystal was successfully grown and investigated in detail, which belongs to the cubic system with a space group of I a-3d. The X-ray rocking curve of the as-grown crystal implied high crystalline quality. The dislocation defects were revealed by the chemical method. Moreover, the density, thermal expansion coefficient and thermal conductivity were determined. The absorption coefficient at 935 nm and the emission cross-section at 2.911 μm were obtained to be about 15.18 cm−1 and 2.23 × 10−21 cm2, respectively. The lifetime of the lower laser level 5I 7 was shown to decrease from 7.58 to 5.88 ms, while that of the upper laser level 5I 6 basically remained unchanged, suggesting that the co-doped Pr3+ possessed an efficient deactivation effect and was beneficial in attaining population inversions of Ho3+. The corresponding findings illustrate that the Yb,Ho,Pr:LuYAG crystal can serve as a novel promising gain medium for realizing the 2.911 μm laser pumped by ~ 940 nm high-power InGaAs laser diode. • A novel Yb,Ho,Pr:LuYAG laser crystal was successfully grown by Czochralski method. • The crystal possesses a high thermal conductivity, which is helpful in dissipating heat during laser action. • Yb3+ makes the crystal suitable for 935 nm LD pumping and Pr3+ can inhibit self-termination phenomenon. • High absorption coefficient at 935 nm and large emission cross-section at 2911 nm are beneficial in realizing ∼2.9 μm laser. • The Yb,Ho,Pr:LuYAG crystal is a new promising gain medium for realizing 2.911 μm laser. [ABSTRACT FROM AUTHOR]

Yb,Ho:YAP and Yb,Ho,Pr:YAP laser crystals with high optical quality are successfully grown using the Czochralski method. The absorption coefficient and band width of the two crystals at 970 nm are increased because of the doping of Yb 3+ sensitizer. The three strongest fluorescence peaks of the two crystals are located at approximately 2844, 2853, and 2912 nm, which correspond to the 5 I 6 → 5 I 7 level transitions of Ho 3+ ions. Lifetime measurements indicate that the deactivator Pr 3+ ions can efficiently decrease the lifetime of the lower level 5 I 7 from 8.848 ms to 1.258 ms. Energy-transfer mechanisms are also studied and analyzed, and up-conversion luminescence spectra provide the further evidence that Pr 3+ ions can efficiently depopulate Ho 3+ ions at the 5 I 7 level. All these results show that Yb,Ho,Pr:YAP crystal may be a promising laser medium for realizing 2.8–3.1 μm lasers pumped using a 970 nm laser diode. [ABSTRACT FROM AUTHOR]

A series of Ho and Pr doped LuYSGG laser crystals were successfully grown by Czochralski method. X-ray rocking curves indicate their high crystalline quality. Crystal structure and basic parameters are provided by XRD and Rietveld refinement. Combining density functional theory, the bandgaps of YSGG and LuYSGG are calculated to be 3.497 and 3.483 eV, respectively. Particularly, the J-O parameters and emission spectra suggest the LuYSGG is more suitable as host for Ho3+ ions and could achieve better 2.9 μm emission than the YSGG. Meanwhile, the luminescent decay curves show the deactivated Pr3+ ion can greatly narrow the lifetime gap between the 5I 6 and 5I 7 energy levels, which can eventually attenuate effect of self-termination phenomenon on the 2.9 μm emission. • A series of Ho and Pr doped LuYSGG mixed laser crystals are prepared. • Microscopic and bandgap structure of LuYSGG are investigated in detail. • LuYSGG is more suitable for achieving Ho:2.9 μm emission than YSGG. • Pr can effectively attenuate the 2.9 μm self-termination phenomenon. [ABSTRACT FROM AUTHOR]

We demonstrate the influence of gamma-ray irradiation on the propagation loss and laser performance of an Er,Pr:GYSGG single crystal fiber (SCF). The size of SCF is Φ 0.75 mm × 70 mm and the diameter fluctuation is less than ±3.5%. The propagation loss coefficients of the samples are 0.07 and 0.09 dB cm−1 before and after irradiation, respectively, which is almost unaffected. The maximum output powers of 197 and 192 mW on the SCFs before and after irradiation are obtained under a 969 nm laser diode (LD) end-pumping, corresponding to the slope efficiencies of 8.1% and 7.9%, respectively. A very good beam quality factor M x 2 / M y 2 of 1.11/1.13 is achieved. These results imply that the Er,Pr:GYSGG SCF laser can be used as a potential seed source for mid-infrared (MIR) multi-stage amplification laser apparatus applied in radiation environment. • Er,Pr:GYSGG single crystal fiber (SCF) with a diameter of Ф 0.75 mm is prepared. • Effect of 100 Mrad 60Co gamma-ray irradiation on Er,Pr:GYSGG SCF is demonstrated. • Output power of 192 mW and M x 2 / M y 2 of 1.11/1.13 are achieved after irradiation. • Both maximum output power and slope efficiency are reduced by only 2.5%. • Er,Pr:GYSGG SCF laser is a potential seed light source applied in radiation environment. [ABSTRACT FROM AUTHOR]

Er3+-doped YAP crystals with concentrations of 5 at%, 10 at%, 15 at% and 20 at% were grown successfully by Czochralski method. X-ray rocking curves suggest high crystalline quality. Lifetime ratio of 4I 13/2 and 4I 11/2 levels decreases obviously with the increase of Er3+ concentrations, which is beneficial to realize population inversion and decrease the laser threshold. Spectroscopy and laser show the 15 at% Er:YAP crystal has strongest mid-infrared fluorescence intensity and best laser performance by 968-nm LD side-pumping. Maximum average powers of 23.52 and 11.08 W are achieved at 250 and 1000 Hz, corresponding to the slope efficiency of 12.0% and 6.2%, respectively. Therefore, the 15 at% Er:YAP crystal is a promising candidate for the high-power and high-frequency mid-infrared laser. • High-quality Er:YAP crystals with four concentrations were grown by the Cz method. • Influences of Er3+ concentrations on the performance of Er:YAP crystals were studied. • Energy transfer and luminescence mechanism in the Er:YAP crystals were analyzed. • LD side-pumped high-power and high-frequency Er:YAP laser is demonstrated. • Maximum average power of 23.52 W was obtained on the 15 at% Er:YAP crystal. [ABSTRACT FROM AUTHOR]

We report on the spectroscopic and laser performance of a novel 30 at.% Er:LuYSGG mixed crystal grown by Czochralski method. The XRC result shows the crystal has a high crystalline quality. A strong absorption peak is located at 966 nm with a FWMH of about 11 nm. The lifetimes of the upper 4I 11/2 and lower 4I 13/2 levels are 1.91 ms and 6.53 ms, respectively. A maximum output power of 909 mW with LD end-pumping is achieved, corresponding to optical-to-optical conversion efficiency of 18.1% and slope efficiency of 21.6%. The laser wavelength of 2794 nm and beam quality factors M x 2 /M y 2 of 1.78/1.83 are displayed. These results indicate that Er:LuYSGG mixed crystal is a promising gain medium for 2.8 μm laser. • The Er:LuYSGG mixed crystal with high optical quality was grown by the Cz method. • It has a longer upper laser level lifetime of 1.91 ms. • A maximum output power of 909 mW with LD end-pumping was obtained. • Results indicate the Er:LuYSGG is a promising gain medium for 2.8 μm laser. [ABSTRACT FROM AUTHOR]

Recently, we proposed GdTaO 4 as a promising high-density scintillator but the scintillation mechanism was still unknown. In this paper, we investigated the temperature-dependent luminescent properties of GdTaO 4 crystal. The emission spectra are characterized by a broad band composed of two Gaussian components located at ~2.2 eV and ~2.7 eV of 8–300 K, which are both thermally quenched with the activation energy of 156 meV and 175 meV, respectively. These two bands are believed to be from different luminescent centers, judging from the excitation spectra, thermal activation energy and decay curves. Additionally, it was also found that the annealing atmosphere exerts little influence on the luminescence intensity. Based on the results, we tentatively assigned the high-energy band to self-trapped excitons (STE) localized in TaO 4 3 − groups and the low-energy band to relaxed excitons related to lattice imperfections. [ABSTRACT FROM AUTHOR]

Er3+-doped YSGG crystals with nine different concentrations were grown successfully by Czochralski (Cz) method. The absorption, emission spectra, and the fluorescence decay curves are investigated comparably. Based on Judd–Ofelt (J–O) theory, the J–O intensity parameters Ω t (t = 2, 4, 6), the experimental and theoretical oscillator strengths are calculated with the absorption spectra. The results show that the 1 at. % lowly Er3+-doped YSGG crystal is more properly used in up-conversion laser applications and 5 at. % Er:YSGG crystal is a better candidate for 1.5 μm lasers within these nine crystals, while the heavily Er3+-doped YSGG crystal is beneficial for the 2.7 μm laser output. But if the doping concentration goes too high, the up-conversion rate of the 4I 11/2 level could be higher than that of the 4I 13/2 level, which would lead to increasing the up-conversion emission and quenching the mid-infrared emission. The 2.79 μm laser performance of LD end-pumped 40 at. % Er:YSGG crystal is also demonstrated. • Er:YSGG crystals with nine different concentrations were grown by Cz method. • The luminescence properties of Er3+ in YSGG crystals are fully researched. • 1 at. % Er:YSGG crystal is more suitable for up-conversion laser applications. • 5 at. % Er:YSGG crystal is a better candidate for 1.5 μm lasers. • A maximum power of 409 mW is obtained at LD end-pumped 40 at. % Er:YSGG. [ABSTRACT FROM AUTHOR]