硯里研究室の学振特別研究員吉田さんの論文"Photochemical Conversion of Ethanolamine-Zn2+ Complex Gel under Vacuum Ultraviolet Irradiation Associated with Color-Tunable Photoluminescence" がACSの The Journal of Physical Chemistry C (IF=4.189)に掲載されました。本成果はROEL吉田研究室との共同の成果です。
https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.1c00318
Abstract
Photochemical conversion of a dry gel coating comprising zinc acetate and monoethanolamine (MEA) into a highly compact and transparent thin film of zinc oxide nanocrystals (ZnO NCs) is shown to produce color-tunable photoluminescence (PL) from violet (389 nm) to bluish-green (486 nm) by controlling the period of vacuum ultraviolet (VUV) irradiation. Transmission electron microscopy (TEM) showed no crystal growth by the prolonged VUV irradiation beyond a size of 4 nm (absorbing at 292 nm), which forms within the first 1 min of VUV exposure. PL excitation spectra showed a peak at either 325 or 370 nm, clearly unmatched with the absorption, indicating that photoexcitation of the ZnO NC core does not contribute to the observed PL. The excitonic state of ZnO rapidly thermalizes and does not contribute to the luminescence via energy transfer. We find that the surface of the ZnO NCs is covered with a highly luminescent Zn–MEA complex with characteristic charge transfer absorption/emission that is responsible for the observed variable PL. This presents a hitherto unknown system of color-tunable PL in which only the “skin” emits, but neither the quantum size effect of the NC core nor the defect states in ZnO contribute. Combined X-ray, IR, and PL spectroscopic techniques suggest that preferential decomposition of acetate is responsible for the color shift during VUV irradiation. Once sufficiently treated with VUV, the PL of the coatings becomes highly stable upon storage under ambient conditions in air. Direct patterning of color-selective PL image was made possible by simply employing a photomask during VUV exposure, as only the irradiated part became luminescent.
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