Temperature dependence of the fast, near-band-edge scintillation from CuI, HgI2, PbI2, ZnO:Ga and CdS:In

We present temperature-dependent pulsed X-ray data on the decay time spectra, wavelengths, and intensities of fast (ns) radiative recombination in five direct, wide-bandgap semiconductors: CuI, HgI2, PbI2, and n-doped ZnO:Ga and CdS:In. At 12 K the luminosity of powder samples is 0.30, 1.6, 0.40, 2.0, and 0.15, respectively, relative to that of BGO powder at room temperature. Increasing the temperature of CuI to 346 K decreases the luminosity by a factor of 300 while decreasing the fwhm of the decay time spectra from 0.20 to 0.11 ns. Increasing the temperature of HgI2 to 102 K decreases the luminosity by a factor of 53 while decreasing the fwhm from 1.6 to 0.5 ns. Increasing the temperature of PbI2 to 165 K decreases the luminosity by a factor of 27 while decreasing the fwhm from 0.52 to 0.15 ns. Increasing the temperature of ZnO:Ga to 365 K decreases the luminosity by a factor of 33 while decreasing the fwhm from 0.41 to 0.21 ns. Increasing the temperature of CdS:In to 295 K decreases the luminosity by a factor of 30 while decreasing the fwhm from 0.20 to 0.17 ns. All emission wavelengths are near the band edge. The luminosities decrease much faster than the radiative lifetimes, therefore, the reduction in luminosity is not primarily due to thermal quenching of the excited states, but mostly due to thermally activated trapping of charge carriers on nonradiative recombination centers. Since the radiative and nonradiative processes occur on different centers, increasing the ratio of radiative to nonradiative centers could result in a class of inorganic scintillators whose decay time and radiative efficiency would approach fundamental limits (i.e. < 1 ns and 100000 photons/MeV). (C) 2002 Elsevier Science B.V. All rights reserved.