Rare Earth-doped TiO2 Research Articles

Synthesis and Luminescent Properties of TiO<sub>2</sub> Materials Single and Triple Doped with Rare Earth Ions (Sm<sup>3+</sup> , Tb <sup>3+</sup> and Eu<sup> 3+</sup>)

Four types of titanium dioxide (TiO2) materials doped with a single kind of rare earth ions Ln3+ (Eu3+, Tb3+, or Sm3+) and three rare earth ions (Eu3+, Tb3+, and Sm3+) were synthesized by the sol-gel method. The compositions, structures, and photophysical properties of these compounds were tested. The structure of the rare earth ion-doped TiO2 samples was characterized by X-ray powder diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR). Optical absorption and fluorescence information was obtained using UV-Vis spectroscopy and fluorescence spectroscopy. The surface morphology of rare earth ion-doped TiO2 materials was observed using scanning electron microscopy (SEM). To further explore the photoluminescent properties of rare earth-doped TiO2 materials for practical applications, small-scale LED light-emitting devices were fabricated.

Review: influence of synthesis methods and performance of rare earth doped TiO2 photocatalysts in degrading dye effluents

Review: influence of synthesis methods and performance of rare earth doped TiO2 photocatalysts in degrading dye effluents

Deciphering the role of (Er3+/Nd3+) co-doping effect on TiO2 as an improved electron transport layer in perovskite solar cells

Charge injection and transport at the interface of the electron transport layer (ETL) and perovskite interface are crucial for the perovskite solar cell (PSC) device performance. Titanium dioxide (TiO2) is well established as a photoanode in numerous solar energy conversion and storage. The bandgap engineering of TiO2 by Rare-Earth (RE)-doping has become a significant way to improve the optoelectronic device performance. This study demonstrates the improved performance of Rare-Earth doped TiO2 (RETO) photoanode based solar cells under the doping of Er3+, Nd3+ and following codoping of the (Er3+/Nd3+) effect. It is note that the Er, and Nd dopants are responsible for producing Ti3+ states and the oxygen vacancies near the surface, which drives the charge transportation much more effectively. With the (Er/Nd) codoping into TiO2, the band structure of TiO2 is modified better to make a quasi-Ohmic contact with the perovskites, by fermi level shifting as well changes in the conduction band minima (ECBM) energy states. This results evidence the preliminary conformation for the improvement of Jsc and Voc. Furthermore, the photoluminescence (PL) emission quenching effects of perovskite-deposited RETO attributes the suppression in the charge recombination. By insight into all these favourable results in the(Er3+/Nd3+) codoped TiO2, the RETO photoanode-based perovskite solar cell (PSC) devices were constructed and exhibited improved photovoltaic properties. The composition of (Er0.002Nd0.002Ti0.996O2) ETL employed PSC reported with a better photoconversion efficiency (PCE %) among all the compositions.

Pulsed laser annealed rare earth doped TiO2 thin films for luminescence and sensing applications

Many research activities target functional luminescent materials based on metal oxides activated with trivalent rare earth ions. Specific applications necessitate optimization of material preparation, annealing and excitation-detection techniques. Hereby we utilized pulsed laser deposition to obtain thin (150 nm) TiO2 films containing 1at% of samarium (Sm) or neodymium (Nd) impurity ions. The effect of pulsed laser annealing (ArF excimer laser, wavelength 193 nm, pulse duration 20 ns) on their structural and luminescent properties was investigated. It was found that, compared to conventional thermal annealing at 700 °C, proper laser annealing (fluence 50 mJ/cm2, 5–15 shots) induced much better crystallization (nearly phase-pure anatase) along with respective improvement of host-sensitized trivalent rare earth fluorescence. The outcome significantly depends on the applied fluence and number of laser shots. Effects of under- and overannealing were witnessed (poor or mixed phase crystallization, weak luminescence and melting/dewetting of the film). A strong luminescence from optimally annealed samples was detected under excitation of 365 nm light emitting diode, which is favorable for potential applications of such thin films. As an example, trace oxygen sensing is demonstrated with the laser annealed TiO2:Sm film.

Detection of Methanol by a Sensor Based on Rare-earth Doped TiO2 Nanoparticles

The rare earth doped TiO2 was prepared and characterized with Nd, Ho and Y as the doping agents, which have obvious absorption in visible light area. The particle size of the glomeration was about 200–400 nm. TiO2 sensor performed a significant change in resistance when exposed to methanol vapor. By comparison, the Nd, Ho and Yb doped TiO2 sensors exhibited a response of 2.22, 4.05 and 3.78, and lowered response and recovery times of 91, 56 and 67 s, respectively. The Ho doped TiO2 showed the best methanol-sensing properties, which exhibited high selectivity and response to methanol compared with the other tested vapors. In concentration of 0–10 ppm, the sensor exhibited excellent stability for detecting methanol at various concentrations.

Evidencing early pyrochlore formation in rare-earth doped TiO2 nanocrystals: Structure sensing via VIS and NIR Er3+ light emission

Er3+ doping of TiO2 colloidal nanocrystals enhances their performance for photo-induced applications. Such doping is known to delay the anatase to rutile transformation under thermal treatment; nonetheless relevant information on the Er3+ light emission and location within the TiO2 structures is still incomplete. Er3+ photoluminescence emission both in the visible (upconverted) and infrared photoluminescence is used for the first time to probe the ions location within the different TiO2 structures. The results show that Er3+ ions in the as-prepared xerogels are not embedded in the anatase crystallites, and only upon thermal treatment Er3+ diffusion is induced into crystal interstitial positions to form a solid solution. At higher temperatures rutile is formed inducing Er3+ segregation and giving rise to the formation of pyrochlore (Er2Ti2O7), as shown by a distinct emission in the infrared spectrum due to the Er3+ ions located within the pyrochlore compound. Although pyrochlore is usually a high temperature phase, analysis of the photoluminescence allows its labeling at temperatures as low as 600–700 °C for small Er3+ concentrations (1 mol %). Increasing Er3+ concentration promotes its enrichment at the nanocrystallites surface accomplished by the anatase-to-rutile phase transformation, suggesting that Er3+ ions control the TiO2 nanocrystals surface properties.

Erratum: “Multicolor and near-infrared electroluminescence from the light-emitting devices with rare-earth doped TiO2 films” [Appl. Phys. Lett. 107, 131103 (2015)

Erratum: “Multicolor and near-infrared electroluminescence from the light-emitting devices with rare-earth doped TiO2 films” [Appl. Phys. Lett. <b>107</b>, 131103 (2015)

Multicolor and near-infrared electroluminescence from the light-emitting devices with rare-earth doped TiO2 films

We report on multicolor and near-infrared electroluminescence (EL) from the devices using rare-earth doped TiO2 (TiO2:RE) films as light-emitting layers, which are ascribed to the impact excitation of RE3+ ions, with the EL onset voltages below 10 V. The devices are in the structure of ITO/TiO2:RE/SiO2/Si, in which the SiO2 layer is ∼10 nm thick and RE includes Eu, Er, Tm, Nd, and so on. With sufficiently high positive voltage applied on the ITO electrode, the conduction electrons in Si can tunnel into the conduction band of SiO2 layer via the trap-assisted tunneling mechanism, gaining the potential energy ∼4 eV higher than the conduction band edge of TiO2. Therefore, as the electrons in the SiO2 layer drift into the TiO2:RE layer, they become hot electrons. Such hot electrons impact-excite the RE3+ ions incorporated into the TiO2 host, leading to the characteristic emissions.

Preparation and Properties of Rare Earth-Doped TiO2 Thin Films by Sol-Gel Process

Rare earth doped titaniumdioxide (TiO2) thin films (rare earth-doped TiO2) have been successfully prepared on a glass substrate by a sol–gel route. After the rare earth-doped TiO2thin films were calcined at 773K for 1h, the effect of rare earth-doping on the properties were investigated using X-ray diffraction (XRD), scanning electronmicroscopy (SEM), ultraviolet–visible spectroscopy and thermogravimetric techniques (TG/DTG). The XRD results showed that rare earth-doped TiO2thin films contained only a single crystalline phase of anatase TiO2after calcining at 773K for 1h. SEM micrographs showed that rare earth-doped TiO2thin films have smooth surfaces containing granular nanocrystallines and are without cracks. The UV–vis absorption spectra showed that the absorption of the rare earth-doped TiO2thin films has a red-shift. From ambient to 1273K, it is about 12% of mass loss because of the volatilizing of water and organic and the phase transformation.

Rare earth-doped TiO2 nanocrystalline thin films: Preparation and thermal stability

A colloidal sol–gel route was used for the synthesis of nanoparticulate TiO 2 and Ln 3+ -doped TiO 2 sols (Ln = Eu or Er; contents of 1, 2, or 3 mol.%), from which the corresponding functional nanocrystalline thin films were subsequently obtained by the dip-coating method. It was found that the as-synthesized sols are not entirely suitable for the preparation of homogeneous thin films due to the water's high surface tension, a problem that is however solved by diluting the sols in ethanol. Appropriate dilution conditions were then determined, and the effect of this dilution on the sol viscosity identified. Finally, the phase composition in the as-deposited condition and the thermal stability of the dip-coated thin films were investigated by X-ray thermodiffractometry up to 1000 °C. It was found that the as-deposited thin films are homogenous and formed by the desired anatase nanoparticles, which eventually start to transform into rutile particles at high temperature. However, no precipitation of titanates occurs in the temperature range investigated. Also, it was observed that increasing the Ln 3+ content improves the thermal stability of these anatase nanocrystalline thin films, an effect that is, if any, slightly more marked for Eu 3+ than for Er 3+ .

Optical properties of rare earth-doped TiO2 anatase and rutile thin films grown by pulsed-laser deposition

Ln3+ (Ln=Tm, Eu and Yb) doped titanium dioxide anatase and rutile films have been grown by pulsed-laser deposition at 700°C under 0.1mbar O2. By using c-cut (0001) Al2O3 sapphire or (100) LaAlO3 single crystal substrates, TiO2 films doped with Ln3+ are constituted with either highly oriented (200) rutile or (004) anatase, respectively. Energy transfer from TiO2 to Ln3+ is studied by photoluminescence spectroscopy with UV excitation (364nm) under band gap excitation of the oxide matrix. It is demonstrated that Tm3+ dopant is not efficient as sensitizers. On the contrary, energy transfer from TiO2 to Eu3+ and Yb3+ occurs in both matrixes, which make this material suitable for down-shifting purpose. Results obtained for Yb3+ compared with our previous study on Nd3+ show that Nd3+ doped-rutile and Yb3+ doped-anatase are the more efficient combinations to convert UV to NIR photon. Finally, a cooperative conversion mechanism is suggested to explain the higher integrated photoluminescence intensity found in anatase Yb3+ rather than in rutile.

Temperature effect of rare earth-doped TiO2 electrorheologicalfluids

Doping of rare earth into anatase TiO2 has been found toimprove the electrorheological (ER) effect of the TiO2; in this paper weinvestigate the temperature dependence of the rheological, dielectric andconduction properties of its ER fluids. Typical cerium-doped TiO2 ERfluid shows the highest shear stress around 80 °C, but that of apure TiO2 ER fluid decreases with temperature beyond 40 °C. Thedielectric constant, loss and conductivity of Ce-doped TiO2 ER fluidincrease with temperature, and it exhibits marked dielectric relaxationaround 70 °C at 1 kHz. However, the dielectric and conductionproperties of pure TiO2 ER fluid is independent of temperature. Thisremarkable difference in the temperature dependence of the dielectric andconduction properties between doped and pure TiO2 ER fluids can wellexplain the different temperature effects of their rheological properties.Furthermore, we preliminarily discuss the above results on the basis oflattice distortion, defects or impurities in TiO2 originating from thesubstitution for Ti4+ by large-radius rare earth ions.