Thermoluminescence and phototransfer thermoluminescence glow curves, and the corresponding emission spectra of LiF (TLD-100) crystals were studied over the temperature range 100 to 300 K after pre-irradiation heat treatment at 373, 423 and 673 K for 1 h. The TL glow curve displays six glow peaks over this temperature range. The intensity and peak temperatures of glow peaks above 200 K are highly affected by the pre-irradiation heat treatment while the glow peaks below 200 K are not affected by this treatment. The various emission spectra include 'ultraviolet' bands at 5.42, 4.42 and 3.57 eV and 'visible' bands at 3.07, 2.65 and 2.22 eV. The first glow peak, seen at 138 K, emits in both the ultraviolet and visible with similar intensity. The next glow peak, seen at 156 K with reduced intensity, also emits in both regions but with relatively more in the ultraviolet than the visible. The peak intensity and energy of the individual visible emission bands are strongly affected by pre-irradiation heat treatment, while the ultraviolet bands are weakly affected. The data are explained with a band-gap model that extends Mayhugh-Christy's model for thermoluminescence above room temperature.