Impact of ligand environment on optical, luminescence and thermometric behavior of A (PO ) :Sm (A = Ca, Sr) phosphors.

The present study investigates the impact of the ligand environment on the luminescence and thermometric behavior of Sm doped A (PO ) (A = Sr, Ca) phosphors prepared by combustion synthesis. The structural and luminescent properties of Sm ions in the phosphate lattices were investigated using powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques. PXRD results of the synthesized phosphors exhibit the expected phases that are in agreement with their respective standards. Fourier-transform infrared (FTIR) spectroscopy confirms the presence of PO vibrational bands. Upon excitation with near ultraviolet light, the PL studies indicated that Sr (PO ) :Sm phosphors exhibit a yellow light emission, whereas Ca (PO ) :Sm phosphors exhibit an emission of orange light. The PL emission results are in accordance with the CIE coordinates, with the Sr (PO ) :Sm phosphors showing coordinates of (0.56, 0.44), and the Ca (PO ) :Sm phosphors displaying coordinates of (0.60, 0.40). Thermal analysis shows improved stability of Ca (PO ) :Sm based on lower weight reduction in thermogravimetric analysis. The effect of temperature on the luminescence properties of the phosphor has been examined upon a 405 nm excitation. By using the fluorescence intensity ratio (FIR) method, the temperature responses of the emission ratios from the Sm : the F  →  H transition to the G  →  H and F  →  H transition to the G  →  H emissions are characterized. The Ca (PO ) :Sm phosphors are more sensitive as compared with the Sr (PO ) :Sm phosphors. The earlier research findings strongly indicate that these phosphors hold great promise as ideal candidates for applications in non-invasive optical thermometry and solid-state lighting devices.