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Nanodiamonds containing silicon‐vacancy centers (SiV‐NDs) are attracting attention as promising fluorescent markers. Recently, the preparation of single‐digit‐nanometer‐sized SiV‐NDs by a detonation process, which can be carried out on a practical scale, has been demonstrated. However, little is known about the effect of these extremely small diamonds fabricated by a detonation process on the electronic state of the SiV centers. In the present study, SiV‐NDs prepared by the detonation process are investigated spectroscopically. It is reported that the extremely small particle size, ≈10 nm, causes an increase of the nonradiative transition probability and an enhancement of the electron–phonon coupling compared with those of typical SiV centers. Because of their electronic states, SiV‐NDs also exhibit a short luminescence lifetime (≈0.56 ns) and a large linewidth (≈14.4 nm) at room temperature. Nevertheless, the fundamental properties of the SiV center, such as the photostability, do not change, irrespective of the particle size.

Yttrium-doped barium zirconate is a solid electrolyte with several properties that are advantageous for fuel cells. We measure photoluminescence and photoluminescence excitation spectra of anhydrous yttrium-doped barium zirconate to characterize the atomic arrangement near the oxygen vacancy because the local structure is known to strongly influence the protonic conduction. The photoluminescence spectra of our anhydrous sintered pellets are composed of three components: recombination at the grain boundary region, recombination at a vacancy defect with an unpaired electron, and the transition of the electronic state of the oxygen vacancy. From the peak position of the latter photoluminescence component and the corresponding photoluminescence excitation spectrum, we can obtain information on the atomic arrangement that Zr is adjacent to the oxygen vacancies. This information is important for the design of materials with high protonic conductivity.

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