Understanding the UV luminescence of zinc germanate: the role of native defects

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Dolado Fernández, Jaime
Martínez Casado, Ruth
Gutiérrez, Rafael
Dianat, Arezoo
Cuniberti, Gianaurelio
Méndez Martín, Bianchi
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Pergamon-Elsevier Science Ltd
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Achieving efficient and stable ultraviolet emission is a challenging goal in optoelectronic devices. Herein, we investigate the UV luminescence of zinc germanate Zn_2GeO_4 microwires by means of photoluminescence measurements as a function of temperature and excitation conditions. The emitted UV light is composed of two bands (a broad one and a narrow one) associated with the native defects structure. In addition, with the aid of density functional theory (DFT) calculations, the energy positions of the electronic levels related to native defects in Zn_2GeO_4 have been calculated. In particular, our results support that zinc interstitials are the responsible for the narrow UV band, which is, in turn, split into two components with different temperature dependence behaviour. The origin of the two components is explained on the basis of the particular location of Zn_i in the lattice and agrees with DFT calculations. Furthermore, a kinetic luminescence model is proposed to ascertain the temperature evolution of this UV emission. These results pave the way to exploit defect engineering in achieving functional optoelectronic devices to operate in the UV region.
© 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. This work was supported by Ministerio de Ciencia, Innovacion y Universidades (Grants MAT2016-75955 and RTI2018-097195-B-I00) and Deutsche Forschungsgemeinschaft (Grant CU 44/47-1). R. M.-C. would like to thank Dr. Giuseppe Mallia for very useful discussions.