Photo-transferred thermoluminescence (PTTL) in LiF TLD-100

An experimental study on PTTL in LiF TLD-100 sample is presented. PTTL is studied as a function of residual TL, wave length of UV light and temperature of sample during UV exposure. The following results are obtained: 1) The relative intensities of individual glow peaks in PTTL glow curve are remarkably different from those of X or gamma-ray induced TL glow curve. The intensity changes are so drastic that peaks 1,2 and 3 can be stronger than peak 5. 2) The efficiency of transfer per unit photon fluence has a maximum value for 230-240nm light in all the sample studied, which indicates that one of the residual traps from where charge transfer occurs resembles closely F and Z3 centres. Charge transfer from another residual trap is most effective with 290nm light. 3) The intensity of PTTL is not proportional to the total residual TL of a sample. It appears that the efficiency of transfer from different types of residual traps is different. Also different residual traps redistribute their optically released charge carriers preferentially amongst the available empty traps. 4) The transfer efficiency is very much dependent on temperature of the sample during UV exposure. This shows that charge release from residual trap is partly by UV photon energy and partly under thermal stimulation. The UV photon excites the charge carrier from residual trap to an intermediate level close to but below the free state, from where thermal stimulation liberates it into the free states. This thermal energy gap is computed to be 0.12 eV