Luminescence of nanocrystalline ZnS:Cu2+

Temperature dependent luminescence and luminescence lifetime measurements are reported for nanocrystalline ZnS:Cu2+ particles. Based on the variation of the emission wavelength as a function of particle size (between 3.1 and 7.4 nm) and the low quenching temperature (Tq=135 K), the green emission band is assigned to recombination of an electron in a shallow trap and Cu2+. The reduction in lifetime of the green emission (from 20 μs at 4 K to 0.5 μs at 300 K) follows the temperature quenching of the emission. In addition to the green luminescence, a red emission band, previously only reported for bulk ZnS:Cu2+, is observed. The red emission is assigned to recombination of a deeply trapped electron and Cu2+. The lifetime of the red emission is longer (about 40 μs at 4 K) and the quenching temperature is higher.