Effect of annealing and hydrogen plasma treatment on the luminescence of hydrothermally grown bulk ZnO

The optical properties of hydrothermally grown bulk ZnO is investigated by low temperature photoluminescence (PL) spectroscopy. The effects of annealing in an argon atmosphere, as well as the influence of hydrogen plasma exposure, on the PL of as-grown material are studied. The 11 K PL spectrum of the as-grown ZnO shows different excitonic lines in the NBE region: several bound exciton lines are clearly visible. The origin of these bound excitons is discussed, as well as the influence of annealing on these lines. A shift in the deep level emission (DLE) is also observed with an increase in annealing temperature: a red shift is detected when the annealing temperature is increased up to 650 °C, while a subsequent blue shift is observed upon an increase in the annealing temperature. The involvement of Li and Cu in this phenomenon will be discussed and the effect of hydrogen on this DLE will also be studied.