Thermally stimulated luminescence of Ca3(PO4)2 and Ca9Ln(PO4)7 (Ln = Pr, Eu, Tb, Dy, Ho, Er, Lu)

The series of whitlockite compounds Ca-3(PO4)(2) and Ca(9)Ln(PO4)(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(PO4)(7) (Ln = Pr, Eu, Tb, Dy, Ho, Er) whereas d-d emission band of the impurity Mn2+ was observed in Mn:Ca-3(PO4)(2) and Mn:Ca9Lu(PO4)(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 Ln(3+)/Ln(4+) ionization potential (IP) of the series, this was interpreted as the inability of these lanthanides to trap a hole. On the contrary Pr3+ in Ca9Pr(PO4)(7), Tb3+ in Ca9Tb(PO4)(7). Dy3+ in Ca9Dy(PO4)(7), Mn2+ in Mn:Ca-3(PO4)(2) and Mn:Ca9Lu(PO4)(7) were identified as hole traps and radiative recombination centers in the TSL mechanism. Ca9Tb(PO4)(7) was found to be a high intensity green persistent phosphor whereas Mn:Ca9Lu(PO4)(7) is a red persistent phosphor suitable for in vivo imaging application. (C) 2010 Elsevier Ltd. All rights reserved.