Effects of dopant concentrations and firing temperatures on decay kinetics of manganese doped willemite nanopowders

Nanocrystallline willemite, Zn_2−xMn_xSiO₄ (0.5≤x≤5 mol%), doped with variable concentration of divalent manganese ions, phosphor powders were prepared using the simple wet-chemical sol-gel method combined with furnace firing at 800, 900, and 1000 °C. X-ray diffraction (XRD) and high resolution X-ray photoelectron (HR-XPS) scans confirm the presence of willemite phase of Zn₂SiO₄. Laser-induced phosphorescence decay measurements of Zn_2−xMn_xSiO₄ nanophosphors were investigated using high peak power pulsed UV nitrogen laser (λ=337.1 nm). The decay curves show non-single exponential behavior with long term decay rate. Various parameters describing the strength of optical transitions in atoms and molecules such as, Einstein's A and B coefficients, ‘f’, integrated cross-section, and transition dipole moment values have been calculated. The long term decay rate of optical transition parameters was found to be somewhat temperature and concentration dependent.