Growth and characterization of single-crystal Er3+:KPb2Cl5 as a mid-infrared laser material

Laser-grade single crystals of Er3+-doped potassium lead chloride (KPb2Cl5) have been grown by a novel modification of the Bridgman method. This new method allows for consistent seeding of a single-crystal growth from polycrystalline material while avoiding any problems with supercooling. An extended in situ annealing step allows strain to relax out of the crystal, reducing cracking problems and improving the quality of the resultant material. These crystals showed significant quantities of depolarized scattering in the visible, concentrated in stacks of parallel planes, but very little scattering in the mid-infrared. Two solid–solid phase transitions were found in this material, and passage through the higher-temperature transition was linked to the formation of the depolarization planes. Measurements were also made of the indices of refraction of all three crystal axes in the near-infrared and mid-infrared, and the orientation dependence of the 4.5 μm fluorescence of Er3+ in this material was examined.