Electron and hole centres produced in zircon by X-irradiation at room temperature

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Abstract
Radiation effects of X-rays in zircon (ZrSiO4) single crystals were studied at RT, by analysing the kinetics and spectrum of the thermoluminescence between 20 degrees and 420 degrees C. The results indicate that some of the electrons produced by the irradiation are captured by Dy3+ impurities apparently substituting for Zr4+ ions, while others are trapped at Si4+ lattice ions. The hole traps include O2- lattice ions near Si3+ or Dy2+ electron centres, as well as other unidentified impurities or point defects. A TL peak at 77.5 degrees C which consists of a broad emission band around 385 nm typical of the SiO44- group is ascribed to the recombination of an electron and a hole trapped at adjacent Si4+ and O2- ions respectively. Its measured activation energy (0.89 eV) is in agreement with the theoretical value (0.87 eV). A series of TL peaks having activation energies of 0.82-1.60 eV and showing the spectral lines of Dy3+ are attributed to electron-hole recombinations at the RE site. The main TL peak at 109 degrees C (E=1.18 eV), which contains both the 385 nm band and the Dy3+ lines, might involve a recombination process which excites both the SiO44- group and the RE ion.