  We generalize and systematize basic experimental data on optical and
luminescence properties of ZnO single crystals, thin films, powders, ceramics,
and nanocrystals. We consider and study mechanisms by which two main emission
bands occur, a short-wavelength band near the fundamental absorption edge and a
broad long-wavelength band, the maximum of which usually lies in the green
spectral range. We determine a relationship between the two luminescence bands
and study in detail the possibility of controlling the characteristics of ZnO
by varying the maximum position of the short-wavelength band. We show that the
optical and luminescence characteristics of ZnO largely depend on the choice of
the corresponding impurity and the parameters of the synthesis and subsequent
treatment of the sample. Prospects for using zinc oxide as a scintillator
material are discussed. Additionally, we consider experimental results that are
of principal interest for practice.
