Raman studies in nanocrystalline lead (II) fluoride

Abstract

Nanocrystalline lead fluoride was prepared by an inert gas condensation technique underultra-high vacuum conditions. Structural studies were carried out with x-ray diffractionanalysis. As-prepared and vacuum annealed samples were found to contain both orthorhombic(α) andcubic (β)phases of PbF2. The annealed samples contain dominantly the cubic phase. Grain sizes were found to be inthe range from 21 to 43 nm. Raman scattering measurements have been performed on thesesamples in different frequency regions. Characteristic phonon vibrational modes such asT2g for β-PbF2 have been observed in addition to some modes corresponding toα-PbF2. The Raman lineswere assigned to β and α-PbF2 on comparison with the already reported, both calculated and experimental, values. Somenew modes have also been observed at the higher frequency region. The modes at higherfrequencies were correlated to vibrations of electronic centres whose density varied withannealing temperature. The presence of electronic centres was investigated byphotoluminescence studies. The widths of the Raman spectral lines were found to decreasewith the increase in grain size. Low-frequency Raman studies revealed the presence ofstructural defect clusters. The defect cluster size was found to increase with annealingtemperature.