Two photoluminescence (PL) components with peaks around 2.8-3.0 and 3.8 eV were induced in hafnium silicates by the irradiation of synchrotron radiation photons at 8.0 eV, while two similar ones were induced in zirconium silicates around 2.7-3.0 and 3.8 eV. By examining PL excitation spectra, PL decay characteristics, and vacuum-ultraviolet absorption spectra, it is assumed that the origin of the PL component around 2.7 (2.8) -3.0 eV is the same as that of the PL component around 2.7-2.9 eV observed in hafnia and zirconia. In the band gaps of hafnium silicates, zirconium silicates, hafnia, and zirconia, luminescent centers responsible for the PL components around 2.7 (2.8) -2.9 (3.0) eV have their respective upper and lower states with a certain constant energy difference that does not change by the hafnium or zirconium content. Electrons (or holes) excited by ultraviolet photons to tail states at the band edges first relax to the upper state of the luminescent centers, and then they are deexcited to the lower state, which induces the PL components.
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