Nanocrystalline PbS prepared onto glass substrates by chemical bath deposition technique are irradiated with 100 MeV Ni 8+ ion beams with different fluences from 1×10 11 to 1×10 13 ions cm −2. Analysis of the samples by X-ray diffraction show increase of average grain size from 11 nm for the pristine samples to 17 nm for the samples irradiated with 1×10 11 ions cm −2. The grain size remains constant at higher fluences. The UV-visible optical absorption measurement also show that band gap of

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... crystalline PbS decreases from 1.9 eV for the pristine samples to 1.7 eV for the samples irradiated with fluences of 1×10 11 ions cm −2 and then remains almost constant. It is observed from photoluminescence (PL) study that the PL intensity increases for irradiated samples with minimum intensity for pristine sample.