In this paper, we evaluated the Ag concentration dependence of the build-up effect of radiophotoluminescence (RPL) in Ag-doped P 2 O 5 -Al 2 O 3 -Na 2 O-SiO 2 (PANS) glasses. After X-ray irradiation, the Ag-doped PANS glasses showed two emission peaks at around 460 and 630 nm, assigned to blue and orange RPL components, respectively. The build-up curves of the orange RPL component had two components corresponding to the formation of the + 2 Ag dimer and Ag 2+ ions. The intensity of the component due to the + 2Ag dimer increased with increasing Ag concentration, whereas that of the component due to Ag 2+ ions decreased. It is assumed that at a high Ag concentration, the Ag + ions have a higher probability of diffusing to Ag 0 sites to form the + 2 Ag dimer because the average distance between neighboring Ag atoms in the glass structure decreases with increasing Ag concentration. Therefore, the intensity of the component due to the + 2 Ag dimer was dominant at a high concentration of Ag in the glass structure.
Transmittance in
porous-glass gas sensors, which use aldol condensation
of vanillin and nonanal as the detection mechanism for nonanal, decreases
because of the production of carbonates by the sodium hydroxide catalyst.
In this study, the reasons for the decrease in transmittance and the
measures to overcome this issue were investigated. Alkali-resistant
porous glass with nanoscale porosity and light transparency was employed
as a reaction field in a nonanal gas sensor using ammonia-catalyzed
aldol condensation. In this sensor, the gas detection mechanism involves
measuring the changes in light absorption of vanillin arising from
aldol condensation with nonanal. Furthermore, the problem of carbonate
precipitation was solved with the use of ammonia as the catalyst,
which effectively resolves the issue of reduced transmittance that
occurs when a strong base, such as sodium hydroxide, is used as a
catalyst. Additionally, the alkali-resistant glass exhibited solid
acidity because of the incorporated SiO2 and ZrO2 additives, which supported approximately 50 times more ammonia on
the glass surface for a longer duration than a conventional sensor.
Moreover, the detection limit obtained from multiple measurements
was approximately 0.66 ppm. In summary, the developed sensor exhibits
a high sensitivity to minute changes in the absorbance spectrum because
of the reduction in the baseline noise of the matrix transmittance.
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