Andrea S. S. de Camargo

Structural and spectroscopic properties of rare-earth (Nd3+,Er3+, and Yb3+) doped transparent lead lanthanum zirconate titanate ceramics

This work presents the structural and spectroscopic characterization of transparent lead lanthanum zirconate titanate ceramics doped with Nd3+, Er3+, or Yb3+ ions. High optical quality samples presenting the perovskite structure were prepared through a mixed oxides method followed by conventional sintering or uniaxial hot pressing. Absorption and luminescence spectra were measured, and radiative emission parameters were calculated for Nd3+- and Er3+-doped samples. The results indicate the potential of these polycrystalline host–ion combinations for the construction of diode-pumped lasers in the near-infrared region.

Iridium(III)–surfactant complex immobilized in mesoporous silicavia templated synthesis: a new route to optical materials

In this work we report the preparation of a new blue-emitting material based on the templated synthesis of mesoporous silica (MCM-41) using micellar solutions of the newly synthesized monocationic metallosurfactant complex bis[1-benzyl-4-(2,4-difluorophenyl)-1H-1,2,3-triazole](4,4′-diheptadecyl-2,2′-bipyridine)–iridium(III) chloride in hexadecyl-trimethyl-ammonium bromide (CTAB). Under ambient conditions, significant increases in excited state lifetime and quantum yield values (up to 45%), were obtained for the solid materials in comparison to the corresponding micellar solutions. Solid state 1H and 19F NMR spectroscopies were successfully employed for quantifying the luminophore content in terms of Ir–surfactant to CTAB and Ir–surfactant to silica ratios.

Local environment of scandium in aluminophosphate laser glasses: structural studies by solid state NMR spectroscopy

The first NMR study of a scandium oxide containing glass system is reported. The influence of scandium substitution for aluminium in the sodium aluminophosphate glass system (NaPO3)0.83–(Al2O3)0.17−x(Sc2O3)x (0 ≤ x ≤ 0.11) has been studied in detail by multinuclear high-resolution NMR experiments. Introduction of scandium into this glass system results in a systematic change in the aluminium speciation: as the substitutional parameter x is increased, aluminium is successively converted from six- to four-coordination. This result suggests that the scandium ions require more non-bridging oxygen atoms for coordination than aluminium in these glasses. 45Sc chemical shifts are consistent with isolated six-coordinated scandium species. 31P{45Sc} rotational echo adiabatic passage double resonance (REAPDOR) curves show a monotonic increase in slope with increasing x, indicating that the number of 31P–45Sc dipole–dipole couplings increases, consistent with a random spatial distribution of scandium. These results rule out the possibility of rare-earth clustering in these glasses. Both the 45Sc MAS-NMR spectra and 45Sc{31P} rotational echo double resonance (REDOR) data indicate that the scandium species adopt a constant, compositionally independent local environment dominated by phosphorus in the second coordination sphere.

Evaluation of the OH− influence on visible and near-infrared quantum efficiencies of Tm3+ and Yb3+ codoped sodium aluminophoshate glasses

This paper presents a throughout spectroscopic investigation of Yb3+∕Tm3+ codoped sodium aluminophosphate glasses in the visible and near-infrared spectral regions. Two sets of samples, prepared in air and nitrogen atmospheres, were characterized by transmission, absorption, luminescence, excited state lifetimes, and upconversion. The data are discussed in terms of OH− contents in the samples, and their influence on Tm3+ fluorescence quantum efficiencies. Besides, a theoretical analysis of radiative properties, by the Judd-Ofelt [Phys. Rev. 127, 750 (1962)]; J. Chem. Phys. 37, 511 (1962)] theory, is also presented in comparison to experimental data. Results indicate that samples prepared in N2 atmosphere, with lower OH− content, present superior properties than those prepared in air. Among these properties are a 30% more extensive infrared transmission of the host matrix, higher emission intensities, and decreased quenching effects, characterizing them as potential materials for high power laser generatio...

Excited-state absorption and 1064-nm end-pumped laser emission of Nd:YVO4 single-crystal fiber grown by laser-heated pedestal growth.

We present an investigation of the excited-state absorption and laser emission of a 1.0-at. %-Nd3+-doped YVO4 single-crystal fiber grown by the low-cost and versatile laser-heated pedestal growth technique. Efficient laser emission at 1064 nm was achieved when the fiber was pumped, in an end-pump cavity, by a Ti:sapphire laser at 808 nm. A continuous-wave threshold of 10 mW was observed with an efficiency of 42% with respect to the absorbed pump power and the maximum output power of 200 mW. These results are excellent when compared with those of a commercial bulk crystal adapted to the same cavity (48% efficiency, 250-mW maximum output power). Thus the fibers are characterized as strong candidates for the construction of compact lasers that can also be pumped by low-cost diode lasers.

Strategies for reducing dye aggregation in luminescent host-guest systems: Rhodamine 6G incorporated in new mesoporous sol-gel hosts

Aiming at the design of new luminescent host-guest materials with minimized aggregation effects, two classes of sol-gel derived mesoporous materials were explored as hosts for Rhodamine 6G (Rh6G) dye: The first consists of pure (SiO2) and phenyl-modified silica (Ph0.17SiO1.915) xerogels, prepared via sol-gel reaction using an ionic liquid as catalytic agent. The second consists of mesoporous sodium aluminosilicate glasses with Si to Al ratio in the range of 6 ≤ Si/Al ≤ 9. Characterization through high resolution solid state NMR proved the successful obtention of the designed host matrices. Following Rh6G-loading in various concentrations, the resulting materials were characterized by their luminescence and excitation spectra, excited state lifetimes, and quantum yields. The dye doped silica xerogels presented high quantum yield values (up to 87%), with no substantial decrease in efficiency with increasing dye concentration. At suitable Rh6G contents, all the final materials presented laser action under 53...

Energy transfer processes in Yb3+–Tm3+ co-doped sodium alumino-phosphate glasses with improved 1.8 µm emission

Sodium alumino-phosphate glasses co-doped with Yb3+ and Tm3+ ions have been prepared with notably low OH− content, and characterized from the viewpoint of their spectroscopic properties. In these glasses, Yb3+ acts as an efficient sensitizer of excitation energy at 0.98 µm—which can be provided by high power and low cost diode lasers, and subsequently undergoes non-resonant energy transfer to Tm3+ ions (2F5/2, , 3H5). Through this process, the emitting level 3F4 is rapidly populated, generating improved emission at 1.8 µm (). In order to guarantee the efficiency of such favorable energy transfer, energy losses via multiphonon decay, Yb–Yb radiative trapping, and non-radiative transfer to OH− groups were evaluated, and minimized when possible. The dipole–dipole energy transfer microscopic parameters corresponding to , and transfers, calculated by the Forster–Dexter model, are CYb−Tm = 2.9 × 10−40 cm6 s−1, CYb−Yb = 42 × 10−40 cm6 s−1 and CTm−Tm = 43 × 10−40 cm6 s−1, respectively.

The polynuclear complex Cu4I4py4 loaded in mesoporous silica: photophysics, theoretical investigation, and highly sensitive oxygen sensing application

The polynuclear complex Cu4I4py4 has been largely studied in solution and in the powder form due to its interesting luminescent properties, which are largely dependent on temperature and pressure. In this work, we present the synthesis of the complex and its wet impregnation in a mesoporous silica host obtained by sol-gel methodology. For optimized loadings, the well-dispersed guest molecules exhibit strong interaction with molecular oxygen, resulting in a significant quenching of the luminescence. The process is highly reversible with a Stern-Volmer constant of Ksv = 33.8, which is the largest value found in the literature for similar complexes in the solid state, suggesting that the new material is a promising candidate for high sensitivity oxygen sensing. Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations reveal a weak intermolecular interaction between the two guest complexes in the excited state, suggesting the formation of an excited state complex (excimer). The assumption of a triplet excimer formation is confirmed by temperature- and concentration-dependent experiments, which provides a new way to explain the giant Stokes shift observed for the guest complex in different media.

Thermal lens and Auger upconversion losses' effect on the efficiency of Nd 3+ -doped lead lanthanum zirconate titanate transparent ceramics

A thorough investigation of optical losses for the 1064nm emission in Nd3+-doped lead lanthanum zirconate titanate (PLZT) transparent ceramics is presented. Thermal lens experiments were carried out to evaluate thermo-optical properties and the fluorescence quantum efficiency of the emitting level 4F3/2. Excited-state absorption losses were measured in the emitting wavelength region, and the Auger upconversion energy transfer parameter γ was calculated. By using γ, the pump-intensity dependence of the optical gain at 1064nm, the fluorescence quantum efficiency, and the generation of heat in the ceramic were simulated for a high 803nm pump-power regime. Since the radiative and nonradiative losses in Nd:PLZT were verified to be considerably lower than in various commercial laser crystals and glasses, it is suggested that this material might become an interesting alternative for high-power laser emission.

Structural ordering in CdxPb1−xF2 alloys: A combined molecular dynamics and solid state NMR study

Molecular dynamics (MD) simulations of binary Cd(x)Pb(1-x)F(2) alloys have been carried out, using a two-body Buckingham interaction potential, leading to a correct description of structural properties as a function of composition and pointing towards an understanding of the eutectic phenomenon. The simulation data can be analyzed in terms of five local fluorine environments Q((n)) (4> or =n> or =0), where n is the number of Pb nearest-neighbor environments. The results suggest a highly nonstatistical population distribution, suggesting an intrinsic phase segregation tendency in the undercooled melt, during the cooling process. This prediction has been tested experimentally for six representative compositions (0.2< or =x< or =0.7) on the basis of high-resolution (19)F solid state NMR data, revealing important similarities between theory and experiment. While the NMR data confirm that the population distribution is, indeed, nonstatistical for all compositions, the results are only found to be consistent with an intrinsic segregation tendency of PbF(2)-rich domains. This tendency manifests itself in substatistical populations of Q((3)) units, resulting in preferred Q((2)) and Q((4)) formations.