Tb~(3+)-doped KPb_2Br_5: Low-energy phonon mid-infrared laser crystal

摘要

Crystals of potassium lead bromide (KPB), a moisture-insensitive low-energy phonon laser host, were synthesized and purified. High-quality undoped and Tb~(3+)-doped (nominal doping concentration was 5 mol % TbBr_3) KPb_2Br_5 were grown by the vertical Bridgman technique. X-ray diffraction measurements indicated that, at room temperature, the material was monoclinic with space group P2_1/c, while at a high temperature the phase transformed to orthorhombic form. A reversible phase transition was observed around 256 ℃ upon the heating and cooling cycle from differential scanning calorimetric measurements. The material was found to be transparent in the broad range from ～0.4 μm to 25 μm and above. The transmission spectrum of a Tb~(3+)-doped crystal showed different absorption bands of Tb~(3+) at 4.5 μm, 3 μm, 2.3 μm, and 2 μm corresponding to ~7F_6-~7F_α transitions, for α = 2-5. The maximum phonon energy of undoped KPb_2Br_5 at room temperature was determined to be 134 cm~(-1) from Raman scattering spectrum.