Growth, thermal, spectral and laser properties of Cr3+/Nd3+ co-doped calcium tantalum gallium garnet crystal
Introduction
Last few years, more and more attention has been paid to the emission of greenhouse gasses such as CO2, NO2, which was caused by the conventional source of energy, and utilization of solar energy is gaining more popularity. In space, solar energy is over 10 times more available than on the surface of the earth. Space solar can be directly transformed into laser radiation with high efficiency, which is unmatched by the light that passes through the atmosphere. Solar-pumped laser is one of the effective systems to utilize solar energy in space, and there is a current desire to find materials that might be employed in solar-pumped lasers. A number of candidate materials, such as Dy2+:CaF2, Nd3+:YAG, Cr3+:Nd3+:YAG, Cr3+:Nd3+:YVO4 single crystals and transparent Cr:Nd:YAG ceramic materials [1], [2], [3], [4], [5], [6], have been studied as the gain media for solar-pumped lasers and good result has been give out, 120 W CW output was obtained by Yabe’s group [7]. As we know, the absorption of Cr3+ ions is matched with the solar light, by the transition of the Cr3+ ions, the energy can also be easily transferred from Cr3+ to Nd3+ [8].
In recent years, many Cr3+/Nd3+ co-doped laser crystal materials has been reported [6], [8]. Calcium tantalum gallium garnet (CTGG) has many excellent properties as a new disordered crystal [9], and we hope Cr3+/Nd3+ co-doped laser crystal could show good performance, so it could be used as solar pumped laser materials. In this paper, we reported the growth of single crystal of Cr3+/Nd3+ co-doped calcium tantalum gallium garnet (Cr3+:Nd3+:CTGG) by Czochralski method. Operated the radio-frequency electromagnetic induction furnace at temperatures in the range of 1630–1590 °C, this crystal was grown along with the [1 0 0] direction. The structure was determined by the X-ray powder diffraction method. The absorption and fluorescence spectra at room temperature were given out. The thermal expansion and specific heat curve were also measured. CW xenon pumped laser operation of Cr3+:Nd3+:CTGG single crystal was demonstrated for the first time, and laser output at 1.06 mm was achieved too.
Section snippets
Synthesis of the polycrystalline materials
Cr3+/Nd3+ co-doped calcium tantalum gallium garnet (Cr3+:Nd3+:CTGG) polycrystalline materials were obtained by conventional solid-state reaction. The starting materials were prepared by mixing Cr2O3, Nd2O3, CaCO3, Ta2O5 and Ga2O3 powder with a purity of not less than 4N. The use of CaCO3 instead of CaO, not only because it’s good stability in air, more importantly, it has a higher decomposition activity, which is conducive to the solid phase reaction. The doping concentrations of Cr3+ and Nd3+
Crystal structure
The XRPD method was used to check the lattice structure of prepared crystal by Bruker-AXS with the model D8 Advance. The powder diffraction data of Cr3+:Nd3+:CTGG were recorded by using a Ni-filtered Cu-target tube and a graphite monochromator. The intensities of the diffraction peak were recorded at room temperature, the 2θ ranged from 10° to 80°, the step size was 0.02°, and the scanning speed was 5°/min. The XPRD pattern is exhibited in Fig. 2.
Compared with the reported CTGG and Nd3+:CTGG
Conclusion
The Cr3+:Nd3+:CTGG crystal has been grown by using the Czochralski method for the first time. The X-ray analysis shows that the structure parameters still belong to the cubic system. It has an average thermal expansion coefficient of 6.78 × 10−6/K and a specific heat of 0.423 J g−1 K−1 at 300 K, it has a lower average thermal expansion coefficient and a high light damage threshold. At room temperature, the absorption peaks were broaden with the doped Cr3+ ions in the range from 300 to 900 nm,
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant no.51472147, 51672161).
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