Probing the exotic emission behaviors of Gd3+ ions in Gd3Ga5O12 wafer via X-ray excited optical luminescence

We investigate the exotic emission behaviors of gadolinium gallium garnet (Gd3Ga5O12, GGG) wafer via X-ray absorption near edge structure (XANES) and X-ray excited optical luminescence (XEOL) in an X-ray nanoprobe beamline. The XANES spectra of the Gd L3 edge and Ga K-edge confirm that both Gd and Ga ions are in the trivalent state in the GGG (100) wafer. The XEOL spectrum exhibits numerous zero-phonon lines (ZPLs) caused by Gd3+ ion transitions. Notably, we observe the quantum cutting phenomenon of Gd3+ ion transitions resulting in red emission due to the 6GJ → 6PJ transition and ultraviolet photon emission due to the 6PJ → 8S7/2 transition. Furthermore, the emission intensities of 6GJ → 6PJ and 6PJ → 8S7/2 transitions increased rapidly with X-ray irradiation time, as observed with time-dependent XEOL. The advantages of using an X-ray nanoprobe, including high peak power density and excellent spatial resolution, allow us to construct XEOL maps to position the enhancing emission intensities of ZPLs in the local area of interest, which can be tuned via X-ray irradiation time. These peculiar emission behaviors of ZPLs in Gd3+ ion transitions may open new avenues in leveraging X-ray nanoprobes to explore quantum materials.