Structural and NIR to visible upconversion properties of Er3+-doped LaPO4 phosphors

Various concentrations of Er3+-doped LaPO4 powder phosphors have been synthesized by the conventional solid state reaction method and are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and upconversion emission measurements. The XRD results show that all the concentration of Er3+-doped samples are assigned to the monoclinic monazite type structure of the LaPO4 phase. An intense green emission band at 547 nm (S-4(3/2) -> I-4(15/2)) along with a weak red emission at 657 nm (F-4(9/2)-> I-4(15/2)) are observed under NIR excitation with 975 nm laser diode. Energy transfer and upconversion fluorescence properties of Er3+-doped phosphors have also been studied. The possible mechanisms involved in the upconversion process have been discussed and compared with other reported systems. (C) 2015 Elsevier B.V. All rights reserved.