Temperature dependence of bulk luminescence from ZnO.

X-Ray excited luminescence (radioluminescence, RL) spectra from nominally pure crystalline zinc oxide (ZnO) are reported. The temperature range is from 20 to 673 K. Significant changes of emission band energies and intensities are observed across the temperature range. Photon energies of emission bands linked to the band gap decrease with increasing temperature in RL. This dependence fits the theoretical equations describing the temperature response of the ZnO band gap. Defect related luminescence includes a complex mixture of features at low temperature for RL. Thermoluminescence (TL) signals from 20 to 300 K confirm the presence of an unresolved feature in the RL data. Comments on the possible origin of these bands are summarized. The data underline that it is essential to record the temperature dependence for the luminescence data in order to separate overlapping spectral features.