Effects of sintering temperature and doping content on luminescence properties of rare earth (Sm+3, Eu3+, and Dy3+) doped natural fluorapatite

Abstract

Fluorapatite (FAP), thermally and chemically stable, has a suitable host structure for rare earth elements (REE). Rare-earth elements doped hydroxyapatite and fluorapatite have been known for a long time and have been studied extensively in industry and literature. In this study, REE doped natural fluorapatites (Ca10(PO4)6F2:xLn3+ (where x ​= ​0.5 ​mol for 1-mol FAP and Ln3+: Sm+3, Eu3+, and Dy3+) sintered at 1150 ​°C for 1 ​h. In addition, Ca10(PO4)6F2:xEu3+ (x ​= ​0.1, 0.5 and 1 ​mol for 1-mol FAP) was also conventionally sintered at 1100 ​°C, 1150 ​°C and 1200 ​°C. XRD, FTIR, SEM, and PL analysis investigated the phase evolution, microstructural development, and luminescence properties of the RE-doped FAP structure. No significant change in XRD and FTIR analysis results was observed with the addition of different rare-earth elements to natural fluorapatite compared to undoped natural fluorapatite. The emission spectra of Sm doped FAP, Eu doped FAP, and Dy doped FAP were recorded with an excitation wavelength of 407 ​nm, 281 ​nm, and 389 ​nm, and the strongest emissions were observed at 608 ​nm, 614 ​nm, and 578 ​nm, respectively. The emission intensity of Eu-doped fluorapatites increases with increasing sintering temperature. On the other hand, the emission intensity does not directly increase with the increasing doping content. The highest luminescent intensity was observed for Ca10(PO4)6F2:1Eu3+ sintered at 1200 ​°C in the red region upon excitation under UV radiation. In this study, ultra-high intensity luminescent materials that emit green and orange light were produced by doping Dy3+ and Sm3+ ions, respectively, for the first time to natural fluorapatite. The luminescent FAPs, produced from waste in an eco-friendly way, can be used in LED and bioimaging applications.