Thermoluminescence in hydroxyapatite

A thermoluminescent (TL) glow peak has been shown to exist at 80 degrees C in synthetic hydroxyapatite, in amorphous calcium phosphate, and in deproteinated rat bone mineral. This TL glow peak is excited by a thermal pretreatment at elevated temperature, followed by exposure to ultraviolet (UV) light. When measured on a cylic TL-readout UV-exposure basis after an original thermal pretreatment, the intensity of this 85 degrees C glow peak displays a logarithmic decay curve characteristic of a transfer thermoluminescence process: A deep trap is activated during the annealing process, and the subsequent UV exposure causes charge transfer to the 85 degrees C glow peak, as is verified using electron spin resonance. Exposure to the atmosphere appears to decrease the TL intensity levels, presumably due to water adsorption; vacuum drying and additional thermal pretreatment reverse this effect on the TL intensities. TL measurements are applied to the comparison of bone mineral samples of varying age. Increases in overall TL intensity are demonstrated between a four-week old normal rat group and eight- and fourteen-week-old normal rat groupings. The TL intensity is also increased by metabolic disorder which causes changes in bone mineral chemistry and crystallography.