Influence of Phase Transition on the Optical Transparency of Lead Fluoride Crystals

Cubic lead fluoride (PbF₂) crystals were grown by non-vacuum modified Bridgman method. Their optical transmission may deteriorate because of oxygen contamination during growth, annealing and machining, storing and carrying. It was found that the role of oxygen is to promote the transformation of β → α phase in the initial cubic structured mono-crystals, which results in the formation of cryptocrystalline or microlithic texture composed of crystalline α-PbF₂ grains. This texture is suggested to be responsible for the transmission loss of lead fluoride crystals.