β-Ga2O3:Cr nanowires with optical microcavities for determining local heating induced by x-ray nanobeams

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This study explores the x-ray excited optical luminescence (XEOL) of optical microcavities fabricated in β-Ga2O3:Cr nanowires (NWs). XEOL measurements reveal prominent luminescence bands in the near ultraviolet-blue (NUV-B) and in the red-near infrared (R-NIR) spectral regions. The NUV-B emission originates from β-Ga2O3 defects, while the R-NIR band is attributed to Cr3+ intraionic transitions. Both spectral regions exhibit sharp resonances, which are analyzed as Fabry–Pérot and whispering gallery mode resonances. Exposure to x-ray nanobeam induces a redshift of the sharp R-NIR peaks, attributed to local temperature increase in the NWs caused by x-ray absorption. The influence of this temperature rise on the NUV-B peaks is also evaluated. In addition, the local temperature increase due to x-ray absorption is estimated through COMSOL finite-difference time-domain simulations, incorporating the material’s physical and thermal properties. This work demonstrates the application of β-Ga2O3:Cr optical microcavities as luminescence-based nanothermometers to probe the localized effects of x-ray nanobeam irradiation.