Study of exciton dynamics in garnets by low temperature thermo-luminescence

Shallow traps that affect exciton dynamics in undoped and Ce doped yttrium aluminum garnet (CeYAG) single crystals were studied by low temperature thermo-luminescence spectroscopy. The nature of traps was identified and their energy levels in the band gap were measured. Three types of traps were found: two very shallow traps with activation energy of less than 0.2 eV associated with electronic defects, one trap with activation energy of 0.5 eV associated with oxygen vacancies, and one relatively deeper trap with activation energy of 0.7 eV associated with hydrogen impurities. The association of oxygen vacancies with shallow traps as evident from this work and with deep traps as reported by Varney et al. [J. Appl. Phys. 111, 063505 (2012)] suggest their presence in the lattice in more than one charge state.