Site selective laser spectroscopy of defects in PbF2, a superionic conductor@fa@f)

摘要

Site selective laser spectroscopy has been used to identify the defect sites in PbF2:Er3+and follow their distribution as a function of dopant concentration and annealing temperature. Three sites labeledS1,S2, andS3 are found to correspond to single Er3+ions with nearbyFprime;icharge compensation, three sites labeledD1,D2, andD3 are found to correspond to clusters (dimer or higher) of Er3+ions with nearbyFprime;icharge compensation, and a cubic site labeledCwhere the Er3+ion is compensated distantly. The cubic site is found to continually increase relative toS1 as the Er3+concentration is raised. This behavior is contrary to that expected from simple mass action relationships, but is similar to that found in other fluorites. As the annealing temperature is raised, the cubic site increases markedly while the other sites decrease markedly over a small temperature range around the superionic transition temperature. This change is direct evidence for the sudden increase in charge screening effects which have been suggested as the driving force for the transition. It is suggested that the additional interactions caused by strain fields exaggerate the Debyendash;Huuml;ckel nonideality corrections and make the screening effects more effective.