Effect of swift heavy ion irradiation on lead sulfide quantum dots embedded in polyvinyl alcohol

The present study compares structural and optical modifications of lead sulfide (PbS) quantum dots under swift heavy ion (SHI) irradiation. PbS quantum dots are prepared following an inexpensive chemical route using polyvinyl alcohol as the dielectric host matrix. SHI irradiation of the samples is carried out with 100MeV Si7+ ion beam with fluences in the range from 1x10(11) to 3x10(13)ionscm(-2) and their structural and optical properties, before and after irradiation, are compared by X-ray diffraction (XRD), photoluminescence (PL) and UV-Vis spectroscopy. The structural parameters of PbS quantum dots are studied by X-ray line profile analysis using the Williamson-Hall plot. The values of average crystallite sizes are found to vary from 8 to 18nm. XRD studies confirmed the formation of the cubic nanocrystalline PbS. Improvement of crystalline quality for lower fluences is exhibited by an increase in the X-ray intensities of the films. The UV-Vis absorption spectra reveal blue shift relative to the bulk material. Size enhancement of PbS quantum dots after irradiation has been indicated in XRD line profiles of the samples which has also been supported by optical absorption spectra. PL studies of all the samples are carried out with excitation wavelength 350nm. A broad PL emission with peak centered at 473nm is observed in pristine as well as all the irradiated samples. PL study also shows that PL intensity increases with ion fluences.