Luminescent properties and particle morphology of Ca3(PO4)2:Gd3+, Pr3+ phosphor powder prepared by microwave assisted synthesis

Nanoparticulate Ca3(PO4)2:Gd3+,Pr3+ phosphor powders were synthesized by microwave-assisted methodology in an aqueous medium. The X-ray diffraction patterns of the nanopowders confirmed the successful crystallization of Ca3(PO4)2 that are consistent with the standard rhombohedral phase of Ca3(PO4)2. The average crystallite size calculated using William-Hall equation was 99 nm. The high resolution field emission electron microscopy data suggest that the powder consisted of an agglomeration of faceted hexagonal particles. Upon excitation with ultra violet (UV) radiation at 274 nm the phosphor exhibited a narrowband emission peak at a wavelength of 313 nm corresponding to the 6P7/2→8S7/2 transition of the Gd3+ ion. Upon co-doping with Pr3+ a broad excitation peak at 222 nm was observed, which was assigned to the 4f-5d transition of the Pr3+ ion. The peak intensity of the UVB emission at 313 nm was shown to improve considerably when excited at 222 nm, suggesting that Pr3+ harvested primary excitation energy and transferred it non-radiatively to Gd3+.