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 (T-q = 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 mus at 4 K to 0.5 mus 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 mus at 4 K) and the quenching temperature is higher. (C) 2002 Elsevier Science B.V. All rights reserved.