Optical properties of LFZ grown β-Ga2O3:Eu3+ fibres

Abstract

Due to their relevance for electronic and optoelectronic applications, transparent conductive oxides (TCO) have been extensively studied in the last decades. Among them, monoclinic β-Ga2O3 is well known by its large direct bandgap of ∼4.9 eV being considered a deep UV TCO suitable for operation in short wavelength optoelectronic devices. The wide bandgap of β-Ga2O3 is also appropriate for the incorporation of several electronic energy levels such as those associated with the intra-4fn configuration of rare earth ions. Among these, Eu3+ ions (4f6) are widely used as a red emitting probes both in organic and inorganic compounds. In this work, undoped and Eu2O3 doped (0.1 and 3.0 mol%) Ga2O3 crystalline fibres were grown by the laser floating zone approach. All fibres were found to stabilize in the monoclinic β-Ga2O3 structure while for the heavily doped fibres the X-ray diffraction patterns show, in addition a cubic europium gallium garnet phase, Eu3Ga5O12. The spectroscopic properties of the undoped and Eu doped fibres were analysed by Raman spectroscopy, low temperature photoluminescence (PL) and photoluminescence excitation (PLE). The Eu3+ luminescence is mainly originated in the garnet, from where different europium site locations can be inferred. The spectral analysis indicates that at least one of the centres corresponds to Eu3+ ions in dodecahedral site symmetry. For the lightly doped samples, the spectral shape and intensity ratio of the 5D0 →7FJ transitions is totally different from those on Eu3Ga5O12, suggesting that the emitting ions are placed in low symmetry sites in the β-Ga2O3 host.