Preparation of large size high uniformity doping Cr2+/Fe2+: CdSe laser crystals by modified VGF method

Abstract

Cr²⁺: CdSe and Fe²⁺: CdSe single crystals are considered promising mid-infrared laser materials owing to the broad absorption and emission bands. As the key component in the laser system, high-quality and large-size active element benefits laser output. However, the preparation of crystals encounters difficulty due to the serious decomposition and high vapor pressure. In this paper, a modified vertical gradient freeze method with a molybdenum crucible was used to grow Cr²⁺/Fe²⁺: CdSe crystals with a size of Φ 51 × 110 mm³. The crystals demonstrated recorded full width at half maximum values of 0.03° in the high-resolution X-ray diffraction rocking curves. The transmittance spectra indicated good Cr²⁺/Fe²⁺ doping homogeneity with the concentration varying only 3 (1.5) times from top to bottom, and the average transmittance exceeded 65 % except the absorption band. Besides, exactly opposite results after the thermal annealing in Se vapors were displayed, and the mechanism was studied in detail. Additionally, the emission spectrum of Cr²⁺: CdSe crystal was measured to be 2.2–3.6 μm, and a preliminary laser experiment was realized with an output power of 20 mW (500 ns,1 kHz) at 2.5 μm. All these results exhibit that the Cr²⁺/Fe²⁺: CdSe crystals fabricated by this method have better quality, and the research may give an effective conference for the preparation of other transition metal-doped II-VI chalcogenides.