Abstract
Herein, we report on the growth of Cr4+–Li2CaGeO4 crystals by the flux growth method from the flux of LiCl, as well as on the effect of doping Li2CaGeO4 with Cr4+ ions on the NIR region spectral properties and crystal structure. The results quantified the occupancy of Cr4+ in Ge4+ sites. The emission spectrum presented broad bands in the NIR region, i.e., 1000–1500 nm excited by 980 nm, with maximum peaks at 1200 nm at room temperature caused by the transition of 3T2→3A2 in Cr4+ ions. The lifetime decreased with the Cr4+ ion doping concentration, specifically from 14.038 to 12.224 ms. The chemical composition and the valence state of chromium in Li2CaGeO4 were analyzed using X-ray photoelectron spectroscopy, which showed that the chromium in Li2CaGeO4 was tetravalent and no trivalent chromium was found. Therefore, the Cr4+–Li2CaGeO4 crystal has a great potential and future in optical applications.
Highlights
Since the first demonstration of the tetrahedral laser action in coordinated tetravalent chromium at the end of the 1980s [1,2,3], Cr4+ -doped media have attracted significant attention in femtosecond [4,5] and tunable solid-state lasers [6,7,8] because they emit very important wavelengths at 1.1–1.6 μm
The crystal structures of all of the samples were checked with X-ray powder diffraction (XRD) (Ultima IV-X) with CuKα radiation at 40 kV and 20 mA at room temperature
Polycrystalline synthesis, crystal growth, and the structure and spectral properties of the Cr4+ –Li2 CaGeO4 crystals were described in this paper
Summary
Since the first demonstration of the tetrahedral laser action in coordinated tetravalent chromium at the end of the 1980s [1,2,3], Cr4+ -doped media have attracted significant attention in femtosecond [4,5] and tunable solid-state lasers [6,7,8] because they emit very important wavelengths at 1.1–1.6 μm. Cr4+ -doped materials have many advantages, including a simple energy level structure, allowing continuous-wave and pulse operation with low threshold pump power, and a broad absorption band overlapping the working wavelengths of several commercial pump lasers [9]. Lasers emitting in this range have increasingly been used in medicine [10], spectroscopy [11], telecommunications systems [12], etc. The fluorescent quantum yield of these media is quite low due to the nonradiative transition of Cr4+ ions; as a result, the quantum efficiency amounts to approximately 9% for Mg2 SiO4 and 14–22% for YAG [22].
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