Laser-induced luminescence associated with surface hydroxide groups in Al2O3

Stoyanovskii, Vladimir O.; Снытников, В. Н.

doi:10.1134/s0023158409030173

Cited by 17 publications

(23 citation statements)

References 15 publications

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“…They reported that a sample consisting of silica sol-gel glasses doped with Ag 0 particles reversibly changed of color several times, from yellowish to darker and vice-versa, through alternate treatments in air at 600 °C and at 60 °C for 24 h or at RT for several weeks. Alternate darkening-bleaching was explained by a phenomenon of reversible aggregation-disaggregation of silver particles (70)(71)(72)(73)(74)(75)(76)(77)(78)(79)(80) nm at 60 °C at RT and 30-60 nm after treatment at 600 °C), leading to an increase-disappearance of a broad SPR absorption centered at 420 nm. The authors also reported that sample darkening occurred in ambient air whether the particles were exposed to natural light or not.…”

Section: Changes Of Size Of Ag 0 Particles And/or In Their Distancesmentioning

confidence: 99%

“…The thin peak at 560 nm corresponds to the second harmonic of the excitation spectrum while the other thin peaks at 367, 373 and the broader one at 382 nm are probably due to impurities contained into the alumina. We could check that they cannot be due to iron impurities as the Fe emission is expected at wavelength higher than 600 nm [79].…”

Section: Photoluminescencementioning

confidence: 99%

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On the origin of the changes in color of Ag/Al2O3 catalysts during storage

et al. 2019

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Despite the large number of catalytic studies involving Ag/Al2O3 catalysts, especially in deNOx reactions, the phenomenon of ageing observed during catalysts storage after preparation by impregnation followed by a calcination treatment, has not been reported earlier and rises questions. The present paper highlights firstly the colors of the calcined Ag/Al2O3 catalysts (white to yellowish) and the associated UV-visible spectra as a function of the Ag loading (0.5 to 4 wt% Ag), and secondly the gradual changes of color to grey/black and the associated UVvisible spectra when the samples are stored in ambient air or in vacuum in a desiccator in dark. These changes were found to be reversible when the samples are re-calcined. The physico-chemical changes in the silver species during ageing were explained thanks to a comprehensive characterization study of the Ag/Al2O3 catalysts after calcination and after ageing. Several techniques such as UV-Visible spectroscopy, XRD, electron microscopy, XAS and photoluminescence were used. After calcination, in addition to highly dispersed Ag + species on alumina, the presence of Agn clusters of size smaller than 1 nm was found to be responsible for the yellowish color of the Ag/Al2O3 catalysts with Ag loadings higher than 2 wt% Ag and for the associated plasmon band at 350 nm. The ageing process was explained based on characterizations, coupled to a close examination of the literature data on the mechanisms of reduction of Ag + species, and on physico-chemical phenomena that can influence the color of various silver-containing materials, such as Ag 0 particle size, aggregation/redispersion and surface alteration. Consequently, the ageing process of the calcined Ag/Al2O3 catalysts, associated to sample darkening and to Ag plasmon band shift and broadening in the entire visible range, was proposed to result from the modification of the nature of the supported Ag phase: the reduction of Ag + species (by auto-reduction and/or photoreduction), followed by the growth of Ag 0 particles, It is proposed that the Agn clusters may act as nucleation sites for the formation of larger Ag 0 particles and that the formation of aggregates is favored by an easy migration of Ag on alumina.

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Section: Changes Of Size Of Ag 0 Particles And/or In Their Distancesmentioning

confidence: 99%

Section: Photoluminescencementioning

confidence: 99%

On the origin of the changes in color of Ag/Al2O3 catalysts during storage

et al. 2019

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“…PL spectroscopy can be used to investigate surface-active sites on the spinel oxide catalysts in connection with adsorption or photocatalytic processes. 30,31 For a variety of catalytically active metal oxide materials, like (iron doped) TiO 2 nanocrystal lms, 32 HfO 2 33 or ZrO 2 34 nanoparticles as well as ThO 2 35 or Al 2 O 3 [36][37][38] bulk materials, it is quite typical to observe a broad emission band with a maximum in the green spectral range. Even if this emission band is well recognized and has been known for decades, the underlying mechanism is still controversially discussed.…”

Section: Introductionmentioning

confidence: 99%

“…31 On the other side, the broad green emission of metal oxides is explained by molecular adsorbates bound to the metal oxide surface. 38,43 The molecular species that are usually linked to the emission are OH groups that are bonded to surface metal cations. 36,38 When exposed to UV irradiation, photoinduced OH radicals can form and be brought into an excited electronic state.…”

Section: Introductionmentioning

confidence: 99%

“…38,43 The molecular species that are usually linked to the emission are OH groups that are bonded to surface metal cations. 36,38 When exposed to UV irradiation, photoinduced OH radicals can form and be brought into an excited electronic state. 44 The vibration properties and thus the subsequent radiative recombination process as well as the emission wavelength are very sensitive to the environment and the binding of the OH species.…”

Section: Introductionmentioning

confidence: 99%

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