Thermally modulated OSL related to the fast component of the OSL signal in quartz

Abstract

The methods of optically stimulated luminescence (OSL) measurements used until recently applied optical stimulation at a constant temperature, with a constant stimulation energy and a constant or linearly increased flux of stimulation photons. During such stimulation the optical cross-section of traps is invariable and it is hard to separate the signals of different origins. It was shown recently that the selective optical emptying of traps is much easier when the optical cross-section is changed during the stimulation. Due to the dependence of the optical cross-section on temperature advantageous changes in this trap parameter can be induced by increasing the sample temperature during optical stimulation. Such a method can be called thermally modulated OSL (TM-OSL). When the experimental conditions are properly selected the TM-OSL curve has the form of a peak. The shape and position of this peak are uniquely determined by the trap parameters and, therefore, curve analysis can be used to estimate the optical depth of the trap (photoionization threshold) and the strength of electron-lattice coupling. These parameters define traps unambiguously and allow a direct correlation of the traps active in the OSL and TL processes to be made. The position of the TM-OSL peak on the temperature axis depends greatly on the stimulation energy, the heating rate and the photon flux used for optical stimulation, so these experimental factors can be used to separate the individual OSL components. This work focuses on the selective detection of the fast component of the quartz OSL signal. The traps responsible for the fast OSL component can be depopulated by light with the wavelength of 620 nm, which is far longer the usual 470 or 530 nm used in OSL measurements of quartz. The results of such experiments, when supported by computer simulations of the thermally modulated OSL process, allow the value of 3 eV to be estimated for the optical depth of traps responsible for the fast OSL component in quartz.