Photoluminescence in SrHfO3 nanocrystals in relation to self-trapped excitons

We investigated the blue emission of wide bandgap SrHfO3 nanocrystals by using 325-nm photoexcitation. The nanocrystals were initially synthesized by using the combustion method, then, as-synthesized crystals were annealed at different temperatures ranging from 700 °C to 1450 °C. With annealing at higher temperatures, the grain size, as well as the degree of crystallinity of nanocrystals increased. Interestingly, in contrast to the bulk case, the SrHfO3 nanocrystals showed a strong blue emission even at room temperature, which could be explained in the framework of self-trapped excitons. A non-monotonic evolution of the visible emission band with increasing annealing temperature was observed due to the combination of the grain size effect and oxygen vacancy formation. The blue emission observed in SrHfO3 NCs was stronger than that observed in a similar material SrZrO3, which might originate from the high dielectric constants in the former.