Synthesis and luminescence studies of Ce doped SrS nanostructures

Cerium doped strontium sulfide nanostructures were synthesized by the solid state diffusion method in the presence of sodium thiosulfate. XRD confirmed the single phase rocksalt structure of the synthesized samples and the average grain size using the Debye-Scherrer relation is calculated to be 55 nm. TEM micrographs reveal the agglomerated whisker-like morphology with a diametre of 55-60 nm and length of several nanometres, which is in close agreement with XRD results. The effect of dopant concentration on photoluminescence (PL) intensity has been studied. PL emission for SrS : Ce (0.5 mol%) is at 481 nm with a shoulder at 530 nm at an excitation wavelength of 430 nm, which is attributed to the transitions from the 5d state to the 4f (2f7/2, 2f5/2) states of Ce3+. Ultraviolet and visible (UV-VIS) spectroscopy shows band-to-band absorption at 273 nm (4.54 eV), which is blue shifted in comparison to the band gap of bulk SrS (4.2 eV), which may be due to quantum confinement. The effect of high energy ball milling on the grain size and PL intensity has also been investigated for the first time in the doped SrS system. The PL emission wavelength is blue shifted by 3 nm but the emission intensity decreases unexpectedly as the milling time increases, although there is a reduction in size which is evident from XRD peak broadening of the milled samples. This may be ascribed to surface defects generated by ball milling which act as killing centres, quenching the PL.