EPR and luminescence of [F.sup.+] centers in bulk and nanophosphor oxyorthosilicates

The main thermally stimulated luminescence glow peak in irradiated oxyorthosilicates occurs near 360-400 K and has been postulated to comprise an electron trapped at an oxygen vacancy ([F.sup.+] center). We have used electron paramagnetic resonance spectroscopy to identify this defect in [Ln.sub.2]Si[O.sub.5] : Ce (Ln = Lu and Y) and show that it consists of a single electron trapped at a non-silicon-bonded oxygen vacancy in both bulk and nanophosphor oxyorthosilicates. Both Lu- and Y-based nanophosphors form seven- and nine-oxygen coordinated structures ([P2.sub.1]/c) whereas the bulk phosphors form six. and seven-oxygen coordinated structures (C2/c). In each case the [F.sup.+] center predominately forms at the larger oxygen site. A typical resonance comprises a single Gaussian line broadened by hyperfine interaction with g-values near the free electron value and hyperfine coupling ~0.4 mT. The [F.sup.+] center can be annealed and radiation-induced, consistent with the thermally stimulated luminescence glow peak behavior. Index Terms--Electron paramagnetic resonance, [F.sup.+] center, luminescence, oxyorthosilicates.