Luminescent properties and particle morphology of Ca₃(PO ₄)₂:Gd³⁺, Pr³⁺ phosphor powder prepared by microwave assisted synthesis

Nanoparticulate Ca₃(PO₄)₂:Gd ³⁺,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 Ca ₃(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 ⁶P _7/2→⁸S_7/2 transition of the Gd ³⁺ 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⁺.