Associated Donor-Acceptor Luminescent Centers in Zinc Sulfide Phosphors

Abstract

Zinc sulfide activated with copper or silver and coactivated with gallium or indium shows two emission bands. The shorter wave-length band does not involve the ground state of the coactivator or donor, whereas the longer wavelength band does. Both bands involve the ground state of the activator or acceptor. The factors contributing to the emission intensities from the various associated donor-acceptor pairs are discussed theoretically. The dependences on temperature and on concentrations of activator and coactivator are in accord with the longer wave-length band involving a highly associated donoracceptor pair. In addition, the energy levels of the donors, as obtained from thermoluminescent data, are correlated on the basis of the model with the differences in the transition energies of the two emission bands of these phosphors.Zinc sulfide phosphors coactivated with Group III elements of the Periodic Table have been reported to have a long wave-length emission band in addition to the short wave-length emission band associated with activation by Group I elements and with self-activation. KrSger and Dikhoff (1), for example, reported long wave-length emission in phosphors coactivated with Sc, Ga, or In. The emission bands peaked at 5250A with Sc, 5700A with Ga, and 6800A with In and were relatively independent of the identity of the activator. They also observed that the substitution of ZnS in part by CdS had less effect on the long wave-length emission spectra than on the short wave-length emission spectra. Klasens (2) attributed these long wave-length bands to the radiative recombination of a free hole with an electron trapped at the coactivator. Froelich (3) reported long wave-length emission for Cu and self-activated ZnS phosphors which were coactivated with quite high concentrations of A1. Emission peaks are at 5880 and 5000A, respectively. Apple (4) has reported that the crystalline structure influences the relative intensities of the two emission bands observed with ZnS: x(Cu, Ag, Au), y(Ga, In) phosphors in which x K y. The long wave-length emission was found to be enhanced in hexagonal ZnS. He has suggested that this effect may be related to a change in association of activator and coactivator.In this investigation a comprehensive study of ZnS:x(Cu or Ag), y(Ga or In) was made. The spectra of the long wave-length emission are found to depend on the identities of both activator and coactivator. The relative intensities of the long and short wave-length emission depend on concentrations of activator and coactivator and on temperature of excitation. These experimental results are explained by means of a model for the long wavelength emission center consisting of a highly associated activator-coactivator center. This center is similar to the associated donor-acceptor system proposed by Prener and Williams (5) to explain the short wave-length emission by radiative transitions from excited states of the donor to the ground state of the acceptor but is different in that the donor and acceptor responsible for the...

X-ray studies and luminescence of ZnS-phosphor doped with silver and cobalt

“…This leads to the proposal that the long wavelength band involved transition between highly associated donor-acceptor pairs. This phenomenon has been noted by other workers [10][11][12][13][14].…”

“…The height of the green band would never exceed 10 to 25% of the main (blue) band. A comprehensive study on ZnS : (Cu or Ag) : (Ga, In) was made by Apple and coworkers [10][11][12][13][14]. Two emission bands were observed in each series.…”

Luminescence in hexagonal zinc selenide crystals

“…At 7 7 "~, the Schiin-Klasens model (Schon 1942, Klasens 1946) is valid, which suggests a transition between an electron in the conduction band and a trapped hole ; while at 4 . 2 "~, the Prener-AppleWilliams model Williams 1956, Apple andWilliams 1959) which suggests a transition between a trapped electron and a trapped hole is more appropriate. The changeover from one model to the other with temperature may be reasoned by considering the relative lifetimes of the transitions involved.…”

Electro- and photoluminescence of compounds based on doped zinc sulfide in the 500–750-nm range

“…The photoluminescence spectrum of ZnS:In (curve 3) consists of at least three bands with maxima at 510, 600, and 640 nm. In [8,9], these bands at λ max = 600 and 640 nm are assigned to the presence of In in ZnS. Simultaneous doping of the ZnS powder with CuCl and In impurities led to a still greater shift of the photoluminescence spectrum to the longwave side up to the IR region.…”