TOF SIMS analysis and enhanced UVB photoluminescence by energy transfer from Pr3+ to Gd3+ in Ca3(PO4)2:Gd3+,Pr3+ phosphor prepared by urea assisted combustion

Abstract

Ca3(PO4)2:Gd3+,Pr3+ phosphors with different concentrations of Gd3+ and Pr3+ were prepared by combustion process using metal nitrates as precursors and urea as fuel. The phosphors were characterized by X-ray diffraction (XRD), Scanning electron microscopy, Time of Flight-Secondary Ion Mass Spectrometry, ultraviolet–visible and photoluminescence (PL) spectroscopies. The XRD patterns were consistent with the standard rhombohedral phase of Ca3(PO4)2 referenced in JCPDS Card No. 70-2065. The average crystallite size calculated using the Scherrer equation at different urea masses was in the range of ∼60–120nm. The PL excitation spectra of Ca3(PO4)2:Gd3+ and Ca3(PO4)2:Pr3+ exhibited peaks at 220–280 and 300–490nm associated with the f→f transitions of Gd3+ and Pr3+ respectively. The ultraviolet B (UVB) emission resulting from the 6P7/2→8S7/2 transition of Gd3+ was observed at 313nm when the Ca3(PO4)2:Gd3+ phosphor was excited at a wavelength of 274nm using a monochromatized xenon lamp. Upon Pr3+ co-doping, the excitation peaks due to Gd3+ and Pr3+ f→f transitions were suppressed and an intense broad excitation peak ascribed to the 4f→4f5d transitions of Pr3+ was observed at 227nm. The peak intensity of the UVB emission at 313nm was shown to improve considerably when the Gd3+ and Pr3+ co-doped systems were excited at the wavelength of 227nm suggesting that the Pr3+ is a good sensitizer of the 313nm narrow line UVB emission from Gd3+.