Tb 3 + -doped KPb2Br5: Low-energy phonon mid-infrared laser crystal

Crystals of potassium lead bromide (KPB), a moisture-insensitive low-energy phonon laser host, were synthesized and purified. High-quality undoped and Tb3+-doped (nominal doping concentration was 5mol% TbBr3) KPb2Br5 were grown by the vertical Bridgman technique. X-ray diffraction measurements indicated that, at room temperature, the material was monoclinic with space group P21∕c, while at a high temperature the phase transformed to orthorhombic form. A reversible phase transition was observed around 256°C upon the heating and cooling cycle from differential scanning calorimetric measurements. The material was found to be transparent in the broad range from ∼0.4μmto25μm and above. The transmission spectrum of a Tb3+-doped crystal showed different absorption bands of Tb3+ at 4.5μm, 3μm, 2.3μm, and 2μm corresponding to F67–Fα7 transitions, for α=2–5. The maximum phonon energy of undoped KPb2Br5 at room temperature was determined to be 134cm−1 from Raman scattering spectrum.