P. Salas

Luminescence and visible upconversion in nanocrystalline ZrO2:Er3+

The structural and luminescence properties of erbium doped zirconium oxide prepared by the sol-gel processes were analyzed. The annealed powders presented a concentration dependent crystallite sizes and crystalline phase, ranging from 28 to 46 nm and from 40 to 96% for the monoclinic phase, respectively. Green (545 nm) and red (680 nm) emissions bands were observed with 489 and 962 nm excitation. Experimental results showed that the emission bands can be tuned by controlling the Er3+ concentration and that the red band is almost quenched with 489 nm whereas it is enhanced with 962 nm excitation. The nature of this behavior is discussed taking into account the nonradiative energy transfer and cross-relaxation process.

Nanocrystalline tetragonal zirconium oxide stabilization at low temperatures by using rare earth ions: Sm3+ and Tb3+

Zirconium oxide was synthesized by the sol–gel method and the tetragonal structure was stabilized up to 1000 °C by doping with different rare earth ions. The evolution of the crystalline structure as a function of the annealing temperature and rare earth concentration of doped and undoped samples were investigated by X-ray diffraction. Our experimental results show that it is possible to obtain up to 73 wt.% of tetragonal content by doping the ZrO2 with 2 mol% of Sm2O3 or Tb2O3 and annealing at 1000 °C. Variations in the lattice parameters and nanocrystallite size were also obtained. Our results suggest that the stabilization of tetragonal structure can be obtained with other rare earth ions.

Concentration enhanced red upconversion in nanocrystalline ZrO2:Er under IR excitation

The effects of Er3+ concentration in ZrO2 on the red (680 nm) and green (545 nm) upconversion emission from Er3+ under near infrared radiation (NIR) excitation (at both 1438 and 962 nm) are presented. For the highest Er3+ concentration used, the red band is almost quenched under VIS (489 nm) excitation, whereas it is enhanced under NIR excitation. Such a difference between photoluminescence and upconversion is explained taking into account the concentration dependent cross-relaxation process (2H11/2 + 4I15/2) → (4I9/2 + 4I13/2). Experimental results suggest that two- and three-photon upconversion processes are taking place under 962 nm and 1438 nm excitation, respectively.

Thermoluminescence and optically stimulated luminescence properties of nanocrystalline Er3+ and Yb3+ doped Y3Al5O12 exposed to β-rays

The thermoluminescence (TL) and optically stimulated luminescence (OSL) characterization of Er3+ and Yb3+ doped Y3Al5O12 nanocrystalline samples prepared by the precipitation process and exposed to β-rays are discussed. The TL as well as the OSL were two orders of magnitude higher in Er3+ doped than in Yb3+ specimens. The charge trapping and the radiative thermally stimulated recombination processes in Y3Al5O12u2009:u2009Er3+ involve four trapping states at 166, 243, 342 and 424u2009°C, but just two trapping levels at 219 and 413u2009°C for Y3Al5O12u2009:u2009Yb3+ at a heating rate of 10u2009°Cu2009s−1. The photostimulation with 470u2009nm light causes in both phosphors a radiative recombination of the optically free charge carriers belonging to the same trapping states. The TL and the OSL as a function of radiation dose behaviour were linear in the 10–100u2009Gy dose range. The results provide evidence of the potential uses of these materials in radiation storage and dosimeter devices.

Nanoparticle-enhanced thermoluminescence in silica gels

The results of transmission electron microscopy and thermoluminescence (TL) studies in silica samples containing Fe and Cu nanosized particles show an important enhancement of their TL response when compared with known reports for pure silica samples. The effect of surface electronic states in the nanoparticles, interacting with the matrix, may be responsible for this new size-dependent effect.

Synthesis and photoluminescence of Y 2 O 3 : Yb 3+ -Er 3+ nanofibers

The influence of the solvent ratio in the hydrothermal synthesis of co-doped Y2O3:Yb3+-Er3+, via CTAB complex, is presented. The nanophosphors for two different ethanol/water solvent ratios, 1:1 and 1:3, shown the following features: the samples exhibit cubic phase, TEM image of the sample synthesized using a 1:3 solvent ratio shows a homogeneous nanofibers morphology in opposition with the sample obtained from a 1:1 solvent ratio which reveals different morphologies prevailing big irregular particles. In both cases the absorption spectra are similar as well as the upconversion emission. These results suggest that the solvent ratio plays an important role in the morphology and on the luminescence properties of the nanostructured materials.

Improving then-pentane hydroisomerization of Pt/SO42−SiO2) catalysts through mixing with ZrO2

The performance of Pt catalysts supported on sulfated zirconia-silica with different stoichiometries is investigated in then-pentane hydroisomerization reaction. Comparatively, with respect to the Pt/SO42−-SiO2 or Pt/SO42−-ZrO2 catalysts, the sulfated mixed oxides show an enhancement of the catalytic activity that increases with the content of ZrO2, reaching its maximum at values between 10 and 15 wt% zirconia. The characterization of the samples reveals that at this stoichiometry occurs the highest H2-consumption of the samples as well as the top value of strong Brónsted acid sites according to the TPD-H2 and FTIR measurements of absorbed pyridine respectively. That is, close to these percents of zirconia content one has a compound that is homogeneously mixed and above those values the segregations of the single oxides occur as verified by X-ray diffraction characterization.

Temperature effect in the crystallite size and the photoluminescence of nanocrystalline ZrO2:Sm3+ phosphor

Nanocrystalline ZrO2:Sm3+ doped at 2 mol% was prepared by sol-gel process and the structure and photoluminescence characterization as function of the annealing temperature were performed. Strong visible fluorescence emission produced by transitions 4G5/2→4H5/2,7/2,9/2 of Sm3+ was obtained by energy transfer process exciting the host at 320 nm and by direct excitation at 408 nm. The experimental results show a quenching of the emission bands by reducing the annealing temperature that is associated with a high content of tetragonal structure. Furthermore, an important change in the structure of the signal emitted was observed when ion was excited directly and the annealing temperature was reduced. These results suggest the possibility to tune the emission of ZrO2:Sm3+ nanophosphor.

Second-harmonic imaging of ZnO nanoparticles

ZnO nanocrystallites of average size 20 nm, agglomerated into ~300nm irregular nanoparticles, were prepared by a hydrothermal method. Laser excitation yielded brilliant second-harmonic generation which was imaged with mum resolution, suggesting good potential for biomedical applications.

Visible emission of rare-earth-doped ZrO2 nanocrystalline phosphor under UV and IR excitation

The photoluminescence and crystalline structure characterization of undoped and several samarium and erbium doped ZrO2 samples are reported. Strong visible fluorescence emission produced by the transitions 4G5/2→6H5/2,7/2,9/2 of Sm3+ was obtained by the excitation of the host at 320 nm (downconversion). Green (545 nm) and red (680 nm) emissions bands were observed under 962 nm excitation (upconversion). Experimental results showed that the emission bands could be tuned by controlling the Er3+ concentration. In particular, for the highest Er3+ concentration, the red band is enhanced under 962 nm excitation. The nature of this behavior is discussed taking into account the concentration dependent non-radiative energy transfer (4I13/2 + 4I11/2) → (4F9/2 + 4I15/2) and cross-relaxation (2H11/2 + 4I15/2) → (4I9/2 + 4I13/2) process.