Optically Active TiO2:Er Thin Films Deposited by Magnetron Sputtering

Abstract

Titanium dioxide photoanodes for hydrogen generation suffer from a profound mismatch between the optical absorption of TiO2 and the solar spectrum. To solve the problem of low solar-to-chemical efficiency, optically active materials are proposed. In this work, TiO2 thin films containing erbium were deposited by radio frequency RF magnetron sputtering under ultrahigh vacuum conditions UHV. Morphology, structural, optical and electronic properties were studied. TiO2:Er thin films are homogenous, with uniform distribution of Er ions and high transparency over the visible VIS range of the light spectrum. However, a profound 0.4 eV blue shift of the fundamental absorption edge with respect to undoped TiO2 was observed, which can be attributed either to the size effect due to amorphization of TiO2 host or to the onset of precipitation of Er2Ti2O7 nanocrystals. Near-infrared NIR to VIS up-conversion is demonstrated upon excitation at 980 nm, while strong green photoluminescence at 525 and 550 nm occurs upon photon absorption at 488 nm.

Enhancement of the thermoelastic component of the photoacoustic signal of silicon membranes coated with a thin TiO2 film

“…The influence of measuring instruments can be simply described as electronic filtering (He) which reduces the signal amplitude in the low-frequency range, and acoustic filtering (Ha) which generates typical signal peaks at higher frequencies (Figures 3&4, Appendix I), usually recognized as shaped, or tailored, microphone frequency response [21] I. They are in accordance with the literature values obtained by different methods [22][23][24][25] and our previous research [13,16]. Other important parameters, like Young's modulus of the film ( )…”

“…the same literature[13,16,[22][23][24][25].Based on the composite piston theory[18], obtained( ) signal components -TD, TE and PE, whose amplitudes and phases are shown in Figures 3.a, c & 4a, c in the case of single-layer (Si membranes, Eqs. (8-12)), and Figures 3b, d & 4b, d in the case of two-layer systems (Si membrane + thin TiO2 film, Eqs.…”

Near-infrared to visible and ultraviolet upconversion in TiO2 thin films modified with Er and Yb

“…More details of process steps and parameters are described in our previous work. 28 Thin films were deposited on various substrates: amorphous silica (Q) for investigation of the thin film structure, and to assess the impact of rare earth ions on the optical bandgap of the TiO 2 host, silicon (Si) for observation of the thin film microstructure and further investigation of its structural properties, conducting indium tin oxide glass (ITO) to assess luminescence properties of upconversion photoanodes.…”

“…In our previous works, we investigated both the concepts of external 27 and internal upconverter, 28,29 and we demonstrated the possibility to use TiO 2 thin film photoanodes modified with rare earth ions (Nd 3+ , Er 3+ , Yb 3+ ) in photoelectrochemical cells. 27,29 Thin film photoanodes deposited at 20% O 2 /(O 2 + Ar) flow rate ratio exhibit the best photoelectrochemical properties (high value of photocurrent and rectangular shape of current density versus voltage curves).…”

“…Moreover, red-togreen emission ratio relate to Er 3+ /Yb 3+ concentration ratio as presented by Jung, 26 while blue or UV light emission is observed only for UC materials with high efficiency due to low probability of the three or four photon UC processes. 9 In our previous works, we investigated both the concepts of external 27 and internal upconverter, 28,29 and we demonstrated the possibility to use TiO 2 thin lm photoanodes modied with rare earth ions (Nd 3+ , Er 3+ , Yb 3+ ) in photoelectrochemical cells. 27,29 Thin lm photoanodes deposited at 20% O 2 /(O 2 + Ar) ow rate ratio exhibit the best photoelectrochemical properties (high value of photocurrent and rectangular shape of current density versus voltage curves).…”