Influence of Li+ charge compensator ion on the energy transfer from Pr3+ to Gd3+ ions in Ca9Mg(PO4)6F2:Gd3+, Pr3+, Li+ phosphor

Phototherapy is a renowned treatment for curing skin diseases since ancient times. Phototherapeutic treatment for psoriasis and many other diseases require narrow band ultra violet-B (NB-UVB) light with peak intensity at 313 nm to be exposed to the affected part of body. In this paper, we report combustion synthesis of NB-UVB -313 nm emitting Ca9Mg(PO4)(6)F-2 phosphors doped with Gd3+, Pr3+ and Li+ ions. The phase formation was confirmed by obtaining X-ray diffraction (XRD) pattern and morphology was studied with the Scanning electron microscopy (SEM) images. Photoluminescence (PL) emission spectra show intense narrow band emission at 313 nm under 274 nm excitation wavelengths. Emission intensity was enhanced when Ca9Mg(PO4)(6)F-2 compound is co-doped with Pr3+ ions. Excitation spectra of Ca9Mg(PO4)(6)F-2:Gd3+, Pr3+ doped samples shows broad excitation in ultra violet C (UVC) region. Diffuse reflectance spectra (DRS), obtained by UV-visible spectrophotometer, measures the absorption properties of the material. By applying Kubelka Munk function on the diffuse reflectance spectra, band gap of the material is determined. PL decay curves were examined which indicates efficient energy transfer between Pr3+ and Gd3+ ions. Charge compensation effect was also studied by co-doping Li+ ion in host. Emission intensity was found to increase with the addition of charge compensator. The prepared phosphor has potential to convert UVC light into NB-UVB. The luminescence intensity of Gd3+ shows remarkable increase when it is sensitized with Pr3+, and an addition of charge compensator in the form of Li+, show even better results. This phosphor surely has the potential to be used as phototherapy lamp phosphor. (C) 2017 Elsevier B.V. All rights reserved.