Table 3.

Influence of different doping elements on HA properties and the biomedical applications.

Doping Element	Synthesis Method	Improvements of Photoluminescent Properties	Biomedical Application	References
Terbium	microemulsion-mediated solvothermal process	the particles could be excited by a visible light beam at 400 nm	fluorescent bio-probe	Wang et al., 2010 [60]
	chemical deposition	excitation light is 378 nm when the wavelength of the monitoring light is 545 nm	fluorescent probe	Qiao et al., 2015 [62]
Erbium	microwave-assisted precipitation method	red and green emission in the spectra	sensing material	Alshemary et al., 2015 [9]
	Microwave-assisted wet precipitation	photoluminescence spectra—green and red emissions	bone healing process	Alshemary et al., 2015 [9]
	co-precipitation	near-infrared emission peaks ~1540 nm	biomedicine	Pham et al., 2016 [24]
Europium	microwave-assisted synthesis	red luminescence; negligible toxicity for Vero cells	potential tools for biomedical applications	Escudero, 2013 [47]
	wet chemical precipitation in water without the addition of any surfactant	luminescence at peaks at 536, 590, 615, 650, and 695 nm under 397 nm excitation	fluorescent probe for in vivo imaging	Chen et al., 2014 [38]
	simple one-step method using cationic surfactant as a template	red luminescence of Eu3+ (5D0–7F1,2) under UV irradiation	drug delivery disease therapy	Yang et al., 2008 [63]
	precipitation	strong green and red fluorescence by irradiation of blue and green light	biocompatible fluorescent labeling material in biological studies	Han et al., 2010 [64]
	synthetized at low temperatures (37 °C)	red luminescence is photostable; luminescence could be obtained under visible irradiation	bio-probe	Doat et al., 2003 [66]
Europium and Terbium	microemulsion process under hydrothermal treatment	typical emission lines of Eu3+ and Tb3+	carriers for drug release and targeting	Yang et al., 2008 [65]
Lanthanum	wet chemical synthesis method	in vitro bioactivity and biocompatibility	bioimaging phosphor/luminescent labeling materials for bioimaging	Ghosh et al., 2016 [69]
	modified sol–gel method at a low temperature of 100 °C	fluorescence detected under TRITC (Tetramethylrhodamine) and FITC (Fluorescein isothiocyanate) filters using epifluorescence microscopy	fluorescent probes for cellular internalization and biolabeling	Jadalannagari et al., 2014 [71]
	sol–gel route	decrease in the dissolution of the samples as the dopant concentration increases	implant in biomedical field	Ahymah, 2011 [72]
Dysprosium and Europium	co-doping	increased photoluminescent properties; strong transverse relaxation effects	contrast agent for MRI in implantology or functional coatings	Tesch et al., 2017 [67]
Dysprosium	co-precipitation	fluorescent character—stimulated at 344 or 360 nm	bimodal probes with low toxicity	Sánchez et al., 2015 [6]