Optical and vibrational properties of CaZnOS: The role of intrinsic defects

The development of new luminescent materials for lighting applications or stress sensors, mechano-driven lighting devices is a crucial technological topic. Materials suitable for these applications should guarantee a high chemical stability, easiness and green sintering procedure and optimal optical properties. In this framework Calcium Zinc oxysulfide (CaZnOS) represents one of the most promising materials, for its near UV excitation with a broad visible emission, a long phosphorescence and a mechano-luminescence effect that still need to be explored. In this work we report the optical properties and the kinetics of radiative recombination upon intrinsic and extrinsic excitation of pure CaZnOS, assessing the vibrational properties by means of Raman spectroscopy, and corroborated by DFT calculations. The analysis of time resolved measurements at room and low temperature (up to 10 K) give new insight on the distribution and nature of the defects that generate the luminescence upon external stress as well the long phosphorescence. Herein, we also present a model of the intrinsic defects and on the energy transfer mechanism among levels in pure CaZnOS matrix, opening new perspectives also on doped materials and for the development of piezoluminescent devices.