Emission mechanism of thermoluminescence of Li2B4O7

Thermoluminescence (TL) characteristics of Li2B4O7 doped with Cu or some rare earth elements as activator were studied and the emission mechanism of TL was proposed. TL grow curves of Cu-doped crystallized glasses were changed with crystallizing temperature and TL emission was not observed from amorphous Li2B4O7. The change in crystallizing temperature resulted in the change of Cu1+ content in the crystal, which markedly affected the TL characteristics of Li2B4O7. TL intensities did not simply increase with increasing amount of Cu doped, but showed maximum values at about 0.05 mol% Cu. Emission spectra of Li2B4O7 doped with Cu or some rare earth elements similarly showed maxima at about 370 nm. The results in ESR measurements indicated that a part of Cu1+ in Cu-doped Li2B4O7-crystallized glass was converted to Cu2+ by irradiation of X-ray. The shape of 70deg C and 150deg C glow peaks of Cu-doped Li2B4O7 were explained by the 'first order kinetics' model, and the activation energies were estimated to be 0.8 and 1.1 eV, respectively. The emission mechanism of TL was proposed as follows: electron holes created by irradiation were trapped by Cu1+ centers, and after liberated from the trap centers by thermal energy, the holes combined with electrons at electron trap centers, giving rise to the emission of TL. (author)