Nonaqueous reactions between titanium(IV) chloride and alcohols (benzyl alcohol or n-butanol) were used for the synthesis of anatase TiO2 particles, while rutile TiO2 particles were synthesized in aqueous media by acidic hydrolysis of titanium(IV) chloride. The X-ray diffraction measurements proved the exclusive presence of either the anatase or the rutile phase in prepared samples. The photoluminescence of both kinds of particles (anatase and rutile) with several well-resolved peaks extending in the visible spectral region was observed, and the quantum yield at room temperature was found to be 0.25%. Photon energy up-conversion from colloidal anatase and rutile TiO2 particles was observed at low excitation intensities. The energy of up-converted photoluminescence spans the range of emission of normal photoluminescence. The explanation of photon energy up-conversion involves mid-gap energy levels originating from oxygen vacancies.

Synthesis of Eu3+- and Er3+/Yb3+-doped GdVO4 nanoparticles in reverse micelles and their multifunctional luminescence properties are presented. Using cyclohexane, Triton X-100, and n-pentanol as the oil, surfactant, and co-surfactant, respectively, crystalline nanoparticles with ~4 nm diameter are prepared at low temperatures. The particle size assessed using transmission electron microscopy is similar to the crystallite size obtained from X-ray diffraction measurements, suggesting that each particle comprises a single crystallite. Eu3+-doped GdVO4 nanoparticles emit red light through downconversion upon UV excitation. Er3+/Yb3+-doped GdVO4 nanoparticles exhibit several functions; apart from the downconversion of UV radiation into visible green light, they act as upconvertors, transforming near-infrared excitation (980 nm) into visible green light. The ratio of green emissions from 2H11/2 → 2I15/2 and 4S3/2 → 4I15/2 transitions is temperature dependent and can be used for nanoscale temperature sensing with near-infrared excitation. The relative sensor sensitivity is 1.11%K−1, which is among the highest sensitivities recorded for upconversion-luminescence-based thermometers.

ZnO nanoparticles doped with different Eu 3+ percentages were synthesized in water (ZnO:Eu(x%)-W) and other solvents (methanol ZnO:Eu(x%)-M and ethanol ZnO:Eu(x%)-E). X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), optical absorption and photoluminescence (PL) spectroscopy were used for characterization of the nanoparticles. Our results showed influence of europium doping and solvents on size, particles agglomeration, light absorption and photocatalytic activity. Improvement in photocatalytical activity with addition of Eu 3+ doping was detected. Particle size increased with Eu 3+ doping in water samples, while it decreased in methanol. Agglomeration was more prominent in ZnO:Eu(x)-W samples.Greater amount of surface OH groups in case of ZnO:Eu(x%)-M samples was detected by PL, XPS and FTIR measurements. Influence of europium doping, as an electron trap, and surface OH groups, as a hole trap, was studied in sunlight photocatalytic degradation of cationic methylene blue (MB) and anionic methyl orange (MO). Improved photocatalytic behavior was discussed and influence of active species was further investigated using hole and hydroxyle radical scavengers. The degradation pathway of MB and MO, using high performance liquid chromatohraphy (HPLC), is also examined.

Lanthanide-doped vanadate thin films offer (i) a promising platform for luminescence-based noncontact temperature sensing; (ii) ratiometric/self-referencing absolute measurements; (iii) exceptional repeatability and reversibility for multirun uses and a long life cycle; (iv) 2% K(-1) maximum temperature sensitivity (among the highest recorded for inorganic nanothermometers); (v) a temperature resolution greater than 0.5 K; and (vi) the potential for high-resolution 2D temperature mapping.

The spectroscopic properties of different infrared-emitting neodymium-doped nanoparticles (LaF 3 :Nd 3þ , SrF 2 :Nd 3þ , NaGdF 4 : Nd 3þ , NaYF 4 : Nd 3þ , KYF 4 : Nd 3þ , GdVO 4 : Nd 3þ , and Nd:YAG) have been systematically analyzed. A comparison of the spectral shapes of both emission and absorption spectra is presented, from which the relevant role played by the host matrix is evidenced. The lack of a "universal" optimum system for infrared bioimaging is discussed, as the specific bioimaging application and the experimental setup for infrared imaging determine the neodymiumdoped nanoparticle to be preferentially used in each case. V C 2015 AIP Publishing LLC.

Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: El acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription properties of neodymium ions in NdVO4 and of the high neodymium content) as well as to their ultrasmall size that leads to large non-radiative decay rates. Results included in this work introduce to the scientific community ultrasmall NdVO4 stoichiometric nanoparticles as multifunctional photothermal agents that could be considered as an alternative to traditional systems such as metallic, organic or carbon-based nanoparticles.

Presented results indicate that in the selected medium, gamma irradiation at low doses induces the lowering in the GQDs height due to the lower number of graphene layers in their structure. Unexpectedly, irradiation in the same medium at 200 kGy induce a significant increase in GQDs height and caused observable agglomeration.

Eu(3+)- and Dy(3+)-doped GdVO(4) samples synthesized by a high-temperature solid-state method are investigated by fluorescence spectroscopy at 298-750 K. They demonstrate potential for development as thermographic phosphors because the experimental and theoretical temperature dependence of the intensity ratio of the two lines agrees well. Experimental lifetime measurements recorded at 10-750 K were fitted using three theoretical models: multiphonon relaxation, temperature quenching through the charge transfer (CT) region, and our modified CT model (TDCT), which considers the temperature dependence of CT energy. The TDCT model yields the best results with good agreement between experimental and fitted lifetime data.