Emission mechanism in single and co-doped Tb:Eu:CaZnOS

The study of new phosphors requires in-depth knowledge of the mechanisms and radiative emission paths and, with this aim, the study here reported focuses on the emission properties of CaZnOS crystals single doped with Terbium and co-doped with Terbium and Europium. By studying the optical properties and, in particular, the kinetics of recombination with time-resolved luminescence, the de-excitation mechanisms and the charge transfer processes have been established. A fundamental role is played by the defective centers and their efficient energy transfer process to the excited levels of Terbium, the mechanism being also active among co-doping rare earths (from Tb3+ to Eu3+), allowing further tuning of the emission properties. Beside photoluminescence, the study shows that in case of mechanical stimulus as well, the mechano-luminescence follows the same path, where the defective states of the matrix efficiently excite the levels of dopants, producing a green emission at 545 nm from Tb3+ and a red emission above 600 nm from Eu3+. Therefore, studying the relative ratio of dopants, it is shown how precisely tune across the visible part of the spectrum the mechano-luminescence emission.