Evidence of upconversion luminescence contribution to the improved photoactivity of erbium doped TiO2 systems

Abstract

Er 3+ -TiO 2 synthesized by a surfactant free hydrothermal method exhibits good photoactivities under sun-like excitation for the degradation of phenol. The presence of Er 3+ does not affect the structural and morphological features of the TiO 2 significantly. The best photocatalytic performance was attained for the samples with 2 wt% of Er. Different photocatalytic runs indicated that the incorporation of the Er 3+ cation would be responsible for the enhanced photocatalytic activity, which participates in different mechanisms under UV and NIR excitation.It is widely accepted that the photocatalytic technology based on semiconductor photoactive materials provides a feasible route to achieve two important processes for environmental control and producing energy, such as pollutant degradation and hydrogen production. 1 Nowadays, the environmental problems demand increasingly severe regulations that open up opportunities for novel green photocatalytic routes leading to the alternative materials to traditional TiO 2 . 2 In order to improve the photocatalytic process, the utilization of solar light as efficiently as possible has been largely pursued. Thus, the use of visible light photons constitutes the key point for a good photocatalyst performance under sunlight conditions. For this scope, different strategies have been traditionally followed, in all cases for the improvement of visible photon absorption. Among these, doping of TiO 2 with hybrid atoms or coupling of TiO 2 with other semiconductors with low band gaps have proved to be viable ways to allow the extension of the light absorption edge. [3][4][5] An alternative option consists of the creation of new single phase visible active catalysts which would overcome the drawbacks of doping. [6][7][8] The other challenging composite configuration, rarely in use but currently under exploration, consists of the combination of a luminescence material with a photoactive catalyst. 9,10 Within this configuration the exploitation of the radiation range not absorbed by the photocatalysts would be achieved. This approach appears to be a completely new alternative for enhancing the efficiency of the photocatalytic process by a wise handling of the arriving photons. It is clear that non-interacting photons drastically diminish the quantum yield under solar irradiation conditions. Thus, the combination of the photocatalytic system with the so-called phosphor material (formed by luminescent ions on a host matrix) which could handle and transform the incoming sunlight radiation turns out to be an interesting and not yet fully explored highway. The applications of the up-conversion process by phosphor-like systems (e.g. NIR or visible to UV) would optimize the photocatalytic performance of traditional UV active photocatalysts. 11,12 Among various up-converting nanomaterials, Er 3+ -based compounds constitute an interesting option for this purpose which could be excited by NIR or visiblelight, showing luminescence in the visible and UV regions. 13 Therefore, the assembly of TiO ...

Improved O2 evolution from a water splitting reaction over Er3+ and Y3+ co-doped tetragonal BiVO4

“…[18][19][20][21] Within this configuration we have recently described the assembly of TiO 2 with Er 3+ acting as the up-converting doping cation. 22 From those results, we proposed that the presence of Er 3+ doped into TiO 2 as a host matrix favors a double mechanism, under UV and vis-NIR excitation. We have also stated that Er 3+ -doping on BiVO 4 clearly stabilizes the tetragonal structure.…”

“…A similar effect has already been observed for Er 3+ doped TiO 2 , for which an up-conversion mechanism would be responsible in part for its better photocatalytic behaviour under vis-NIR irradiation. 22,34 The durability of the Er,Y-BiVO 4 system was evaluated through recycling the used catalyst (Fig. 7).…”

Upconversion Nanoparticles for Other Applications

“…In 2012, Obregón and Colón [57] In 2011, Yan et al [58] presented the fabrication of highly ordered crystallized mesoporous TiO 2 stabilizing at a temperature as high as 700°C; by introducing rare earth elements in the synthetic process, they successfully achieved the NIR photocatalytic degradation of rhodamine B by the ordered mesoporous TiO 2 doped with Yb 3+ and Tm 3+ . The UV-Vis-NIR absorption spectrum of the TiO 2 :Yb 3+ ,Tm 3+ sample exhibits two strong absorption bands (Fig.…”

Towards near-infrared photosensitization of tungsten trioxide nanostructured films by upconverting nanoparticles

“…Given their optical properties, upconverting (UC) materials are presently investigated for biomedical [76,77,78], photocatalysis [79,80,81,82] and solar energy conversion applications [50,83,84,56]. Indeed, in UC materials the excitation of the higher energy emitting states occurs via the sequential excitation of multiple NIR photons.…”