Thermally stimulated luminescence of Ca-3(PO4)(2) and Ca(9)Ln(PO4)(7) (Ln = Pr, Eu, Tb, Dy, Ho, Er, Lu)

Abstract

The series of whitlockite compounds Ca(3)(PO(4))(2) and Ca(9)Ln(PO(4))(7) (Ln = Pr, Eu, Tb, Dy, Ho, Er, Lu) was studied in radioluminescence (RL) and thermally stimulated luminescence (TSL) excited by X-rays. f-f emission lines of Ln(3+) were observed in RL for Ca(9)Ln(PO(4))(7) (Ln = Pr, Eu, Tb, Dy, Ho, Er) whereas d-d emission band of the impurity Mn2+ was observed in Mn:Ca(3)(PO(4))(2) and Mn:Ca(9)Lu(PO(4))(7) at 655 nm. In TSL, the Eu, Ho and Er compounds did not show any signal. As Eu3+, Ho3+ and Er3+ present the highest Ln3+/Ln4+ ionization potential (IP) of the series, this was interpreted as the inability of these lanthanides to trap a hole. On the contrary Pr3+ in Ca(9)Pr(PO(4))(7), Tb3+ in Ca9Tb(PO4)(7). Dy3+ in Ca(9)Dy(PO(4))(7), Mn2+ in Mn:Ca(3)(PO(4))(2) and Mn:Ca(9)Lu(PO(4))(7) were identified as hole traps and radiative recombination centers in the TSL mechanism. Ca(9)Tb(PO(4))(7) was found to be a high intensity green persistent phosphor whereas Mn:Ca(9)Lu(PO(4)(7) is a red persistent phosphor suitable for in vivo imaging application.