Thermoluminescence in Quartz

Abstract

X‐ray‐ and uv‐excited thermoluminescence in natural quartz has been investigated by studying the properties of synthetic samples. The results for a large number of natural samples, including single crystals, outcrop specimens, and core‐hole samples showed that most of them had four prominent glow peaks in common. One of these is due to the presence of Ti and the others are apparently associated with a defect center. The effects of annealing at temperatures up to 900°C were found to be important in well‐crystallized samples but unimportant in others. The emission spectrum of the Ti glow peak shows that a number of levels are involved in the luminescent transitions. All of the defect‐center glow peaks have the same emission spectrum which consists of a single maximum with a long wavelength tail. Direct‐current electrical measurements on single crystals showed that the trap‐emptying processes for the defect center were nonlocalized. Optical absorption measurements at room temperature indicated that none of the common absorption bands are associated with peaks in the glow curve. From phosphorescent‐decay measurements it was determined that the trapping levels associated with the defect center have very narrow energy distributions whereas the trapping level due to Ti is discrete. The glow peaks for ordinary quartz are not excitable by uv irradiation, but in samples annealed at 900°C all of the glow peaks due to the defect center are excited by uv. The annealed samples show absorption in the uv region which is not present in unannealed specimens. The results suggest changes in the trap‐filling mechanism, but the effects can also be explained by alterations in the luminescent levels. Luminescence can be excited in all of the samples at fixed temperatures by x rays but not by uv. At low temperatures the effects of transitions through trapping levels are unimportant, and the emission is due only to x‐ray excitation of the luminescent centers. The spectral response of the emission is the same as that for the Ti glow peak. The intensity is about the same in all samples and is not affected by impurity content. This indicates that the luminescent levels involved are due to a crystal defect center and that the same center is involved in the thermoluminescence due to Ti.