We report on the measurement of the absolute external luminescence quantum efficiency of various ZnO samples using a miniature integrating sphere fitted into a cryostat. Even the absolute luminescence quantum efficiencies per spectral interval are directly accessible. Measurements have been carried out on high quality bulk samples and different commercially available ZnO powders from 8K up to room temperature. Activated processes lead to an overall decrease in the efficiency with temperature. All efficiencies are considerably below unity, making the identification of the luminescence decay time with the radiative life time very questionable.

We report the fabrication, transmission electron microscopy investigation and linear optical properties of silver iodide quantum dots in an aluminaborosilicate host network structure. The nearly spherical quantum dots with radii ranging from 1.7 to 2 nm exhibit a pronounced excitonic absorption and intensive intrinsic photoluminescence in the intermediate confinement regime. The selective photoluminescence and photoluminescence excitation measurements revealed the fine structure in the spectra due to the splitting of the lowest exciton state by the electron±hole exchange interaction. A considerable enhancement of the exchange energy with decreasing quantum dot size is observed.

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