Influence of Ce3+ Concentration on the Thermal Stability and Charge-Trapping Dynamics in the Green Emitting Phosphor CaSc2O4:Ce3+
Journal article, 2017
The influence of the Ce3+ concentration on the excitation and emission characteristics, thermal stability, and charge-trapping-detrapping dynamics, of the green-emitting phosphor Ce3+ doped calcium scandium oxide (CaSc2O4) with very dilute Ce3+ substitutions (0.5, 1.0, and 1.5%), has been investigated using optical spectroscopy techniques. The diffuse reflectance and excitation spectra are found to exhibit a nonsystematic behavior with varying Ce3+ concentration, mainly linked to spectral band-overlap, whereas the emission spectra display only minor changes with varying Ce3+ concentration, suggesting that the local structural coordination of the Ce3+ dopants remains the same for different Ce3+ dopant levels. The major impact of Ce3+ concentration is seen on the thermal quenching temperature, which is found to be as high as T-50% approximate to 600 K for the most dilute Ce3+ doping (0.5%), followed by T-50% approximate to 530 K for 1.0% doping and T-50% approximate to 500 K for 1.5% doping, respectively. The materials are found to display a red-shift of the emitted light from 518 to 535 nm with increasing temperature from T = 80 K to T = 800 K, for all Ce3+ dopant levels. Thermoluminescence glow curves provide evidence for five charge-trapping defects, which are found to exhibit different charge-trapping dynamics for excitation into different 5d levels. It is argued that the three deeper traps can be filled by athermal tunneling of charges from the Ce3+ 5d(1) level, while the two shallower traps can only be filled when the charges move through the conduction band of the material.