Photoluminescent (PL) spectra from the SrS:Ce,Sm phosphor following a excitation. The curves a, b, and c refer to different integration time windows over the streak camera images. The intensities of the different spectra (in arbitrary units) have not been normalized.
OSL mechanisms as reviewed in Ref. 18 following the Keller model. During exposure to UV light, electrons and holes are produced in the conduction and in the valence band of the SrS. Part of this energy is stored in metastable levels modifying the valence states of the two activators, initially in the trivalent state: become , while become acting as an electron trap. Under IR stimulation, the trapped electron is ejected via the conduction band, then is recombined with becoming an excited state of . The return to the ground state of gives the observed characteristic emissions. In the same way, at much lower rate, electrons can directly recombine within the levels, emitting a series of weak characteristic lines.
Photoluminescent (PL) decay curve from the SrS:Ce,Sm phosphor following a excitation over a time base. The curve has been recorded in the spectral range corresponding to the main emission. The dotted curve represents the temporal behavior of the , laser pulse as recorded by the streak scope.
Optically stimulated luminescence (OSL) decay curve from the SrS:Ce,Sm phosphor following an excitation over a time base. The curve has been recorded in the spectral range corresponding to the main emission. The trapped charge was previously generated in the material by exposing it for to a constant flux of UV light. The fist stage of the exponential luminescent decay is here again well fitted with a lifetime of . The tail of the OSL is not measurable (n.m.) here since the weak OSL emission falls quickly down to the noise level.
PL and OSL rise∕decay curves from the SrS:Ce,Sm phosphor following 260 and laser excitations over a time base. The dotted curve represents the temporal behavior of the laser pulses as recorded by the streak scope.
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