Local site symmetry of Sm3+ in sol-gel derived α′-Sr2SiO4: Probed by emission and fluorescence lifetime spectroscopy

Trivalent samarium-doped strontium silicate (Sr2SiO4) phosphors were prepared by sol-gel synthesis using tetra ethyl orthosilicate (TEOS) as precursor. The synthesis temperature could be brought down to 600 °C for the formation of a single phase sample. The emission and excitation spectra, and decay curves were employed to study the luminescence properties. The calcined powders of the Sm3+ ions doped in the Sr2SiO4 emit reddish orange light. In our present study, the 4G5/2→6H5/2 (MD) transition of Sm3+ ions is less intense than 4G5/2→6H9/2 (ED) transition. This indicates that Sm3+ ions preferentially occupy asymmetric site in α-Sr2SiO4. Fluorescence life time measurement has shown monoexponential behavior for Sm3+ in strontium silicate with lifetime value of 2.23 ms. Based on lifetime and emission spectra, it can be inferred that Sm3+ occupies 9-coordinated Sr2+ site in strontium silicate. Based on stark splitting pattern it was inferred that site symmetry around Sm3+ is C3v which further justifies it׳s occupancy in 9-coordinated sites. It was observed that, the emission intensity of Sm3+ increases with the increase in concentration initially, reaching maxima at 1.0 mol % and then decreases with the increasing concentration due to concentration quenching. At higher concentrations (x>0.01), however, the observed decay curves were bi-exponential.