BiPO4: A better host for doping lanthanide ions

In the present manuscript it is demonstrated that BiPO4 is a better alternative to lanthanide phosphate host for making lanthanide ion-based luminescent materials. Hexagonal and monoclinic forms of BiPO4 phase were prepared based on the reaction of Bi3+ and PO43- ions in ethylene glycol medium at 100 and 185 degrees C, respectively. From the differential thermal analysis (DTA) studies it is confirmed that the difference in the nucleation mechanism rather than the phase transition is responsible for the monoclinic phase formation at low temperatures (125 degrees C). Monoclinic BiPO4 is quite stable and forms random solid solutions with lanthanide phosphates having both monoclinic (monazite) and tetragonal (xenotime) structures, as confirmed by XRD, FTIR and P-31 solid state nuclear magnetic resonance studies. On excitation corresponding to the S-1(0) -> P-3(1) transition of Bi3+ in BiPO4:Ln samples, energy transfer from host to lanthanide ions takes place. The studies are quite relevant as there is a growing interest all over the world in replacing lanthanide based host used for different applications with easily available, easily purifiable and cheap main group elements (like Sb, Bi etc.) based hosts.