Enhanced UVB emission and analysis of chemical states of Ca ₅(PO₄)₃OH:Gd³⁺,Pr³⁺ phosphor prepared by co-precipitation

Hydroxyapatite (Ca₅(PO₄)₃OH) is a well-known bioceramic material used in medical applications because of its ability to form direct chemical bonds with living tissues. This mineral is currently used as a host for rare-earth ions (e.g. Gd³⁺, Pr ³⁺, Tb³⁺, etc.) to prepare phosphors that can be used in light emitting devices of different types. In this study Ca₅(PO ₄)₃OH:Gd³⁺,Pr³⁺ phosphors were prepared by the co-precipitation method and were characterised by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive x-ray spectroscopy and photoluminescence spectroscopy. The x-ray diffraction pattern was consistent with the hexagonal phase of Ca₅(PO₄) ₃OH referenced in JCPDS card number 73-0293. The x-ray photoelectron spectroscopy data indicated that Ca²⁺ occupied two different lattice sites, referred to as Ca1 and Ca2. The photoluminescence data exhibited a narrowband emission located at 313 nm, which is associated with the ⁶P_7/2→⁸S_7/2 transition of the Gd³⁺ ion. This emission is classified as ultraviolet B and it is suitable for use in phototherapy lamps to treat various skin diseases. The photoluminescence intensity of the 313 nm emission was enhanced considerably by Pr³⁺ co-doping.