We describe the results obtained from a computer simulation of bleachi
ng of thermoluminescence (TL), generation of phototransferred TL (PTTL
) and production of optically stimulated luminescence (OSL) during opt
ical stimulation. The model used in these simulations includes shallow
trapping levels, thermally ''active'' traps from which charge is ther
mally excited during TL readout, deep thermally disconnected traps whi
ch are stable during TL readout, radiative recombination centers and n
on-radiative recombination centers. In the model described, optical ex
citation of electrons is assumed to occur from the thermally disconnec
ted traps only. Recombination of optically excited electrons with trap
ped holes is an important aspect of the model. PTTL, TL and OSL curves
are simulated as functions of absorbed radiation dose and as function
s of illumination time during optical excitation. The results indicate
that a model such as this, in which the key feature is the recombinat
ion of freed electrons with trapped holes, cannot be discounted as the
mechanism for optical bleaching, PTTL and OSL in sedimentary material
s.