Optically stimulated phosphorescence in quartz over the millisecond to second time scale: insights into the role of shallow traps in delaying luminescent recombination

Time-resolved optically stimulated luminescence (TR-OSL) curves from quartz are usually measured over a few hundred microseconds because this time range best illustrates the main component in quartz which lies in the range 30-45 mu s. In this study we present the decay form of quartz TR-OSL and optically stimulated phosphorescence (OSP) covering over 8 orders of magnitude from 50 ns to similar to 8 s. A detailed characterization of the previously unstudied slowly decaying signals (millisecond-second time scales) is undertaken to understand the origin of these components and the role of re-trapping following optical stimulation. We present preheat and stimulation temperature dependence for both the TR-OSL and OSP curves in these time ranges and use the latter data to determine the E and s values for the participating shallow traps. We observe an abnormal decay behaviour seen as a sudden increase in the decay rate (a 'kink') conspicuous at about 2-3 s in the OSP curves measured at 75 and 100 degrees C. We satisfactorily reproduce this behaviour with a numerically solved kinetic model consisting of four energy levels. The physical interpretation of the kinetic rate equations is discussed in terms of a three trap-one centre model or a one trap-two centres model involving localized charge transfer.