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 313nm to be exposed to the affected part of body. In this paper, we report combustion synthesis of NB-UVB -313nm emitting Ca₉Mg(PO₄)₆F₂ 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 313nm under 274nm excitation wavelengths. Emission intensity was enhanced when Ca₉Mg(PO₄)₆F₂ compound is co-doped with Pr³⁺ ions. Excitation spectra of Ca₉Mg(PO₄)₆F₂: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.

Photoluminescence and electron paramagnetic resonance properties of a potential phototherapic agent: MMgF4 :Gd3+ (M = Ba, Sr) sub-microphosphors

Novel narrow band UVB-emitting phosphors, BaMgF₄ :Gd³⁺ and SrMgF₄ :Gd³⁺ phosphors, were synthesized using a co-precipitation synthesis method. X-Ray diffraction analysis was carried out to confirm compound formation, phase purity and crystallinity of the phosphor. At 274 nm excitation, phosphors show a sharp narrow band emission at 313 nm that can be assigned to ⁶ P_7/2  → ⁸ S_7/2 transition of the Gd³⁺ ion. With increasing dopant concentration, intensity enhances and then decreases after a certain concentration, which is an indication of concentration quenching taking place in the phosphor. Scanning electron microscopy images of the phosphor show agglomerated particles in the sub-micron range. Particles range in size from 600 to 800 nm. Electron paramagnetic resonance studies of the phosphors were carried out to detect radicals present in the prepared phosphor. With narrow band UVB emission, phosphor seems to be a good candidate for UV phototherapy application. Copyright © 2016 John Wiley & Sons, Ltd.