1. Could you explain the significance of your article to the non-specialist? 

We found a simple route to fabricate zinc oxide (ZnO) films of high crystallinity and simultaneously enable incorporation of combinations of impurity donor (contributes free electrons) and acceptor (easily takes electrons) ions like indium (In)-lithium (Li) or germanium (Ge)-Li. This technique is used as a tool for fast screening of tailored ZnO crystalline films. Luminescence from the films show ultra fast decay times at wavelengths which are easy to detect by a common photomultiplier. Essentially, we show that a sufficient high amount of In and Li or Ge and Li is indispensable to yield high-intensity emission.

2. What has motivated you to conduct this work? 

Motivation comes from the need of ultra fast scintillator crystals. They are required, for example in medical applications, in time-of-flight positron emission tomography (TOF-PET) devices which enable the detection of initial stage  cancer. In such TOF-PET devices, high-quality imaging due to high spatial resolution and markedly improved signal-to-noise ratio is feasible. One of the subjects that our laboratory is working on is the growth of ZnO bulk crystal and crystalline film. Doping of large zinc oxide crystal, however, is an issue not really solved until now. Moreover, it is time-consuming since the fabrication of suitable crystal size takes up to 3 months and requires high-pressure equipment. Additionally, machining ZnO crystals may generate a defective surface layer, which affects luminescence characteristics upon excitation by low energy radiation like ultra violet. We therefore use our ZnO film technology capable of producing high-quality ZnO films with a mechanically untouched surface.

3. Where do you see this work developing in the future? 

The demand to detect radiation for different purposes is continuously growing. Thin film detectors are thought to take a stake of the whole market due to high two dimensional resolution. The size and weight of devices are reduced as well. Worldwide, researchers are now working on the matter.

4. Are there any particular challenges facing future research in this area? 

A deeper understanding of the luminescence mechanism and the effect of other dopant combinations has not yet been clarified satisfactorily. Both are subject to current research work. A more engineering related task for the most suitable dopant combination is the technology transfer from film to bulk crystal growth.