Elder De la Rosa

Stimulated emission and radiative properties of Nd3+ ions in barium fluorophosphate glass containing sulphate

Abstract Spectroscopic properties of Nd 3+ in barium fluorophosphate glassy matrix containing sulphate have been analysed by fitting the experimental data with the standard Judd–Ofelt theory. Various spectroscopic parameters viz. radiative transition probabilities, radiative decay time, fluorescence branching ratios, electric dipole line strengths, stimulated emission cross sections and optical gain of the principal fluorescence transition from the 4 F 3/2 metastable level are obtained. Results show that addition of sulphate to the fluorophosphate matrix will enhance the fluorescence spectral properties of Nd 3+ considerably. Quantum efficiency of the 4 F 3/2 emission is found to be higher than that of fluorophosphate glasses and stimulated emission cross section of the 4 F 3/2 → 4 I 11/2 transition is the highest among all reported values. Quantitative estimation of the non-radiative processes such as multiphonon relaxation and quenching by water content was carried out and the results show that the water content is below the critical level for optimum laser performance.

Influence of surface coating on the upconversion emission properties of LaPO4:Yb/Tm core-shell nanorods

A solution based hydrothermal method is used for the preparation of LaPO4:Yb–Tm doped and LaPO4:Yb/Tm core-shell upconverted nanorods. The morphologies, structure, formation mechanism, and upconversion emission properties of these nanocrystals are investigated in detail. Tensile strain is observed for LaPO4:Yb–Tm doped material but compressive strain is obtained for LaPO4:Yb/Tm core-shell material. Analysis suggests that the lattice strain plays an important role on the upconversion emission. Bright blue (475 nm) and red (650 nm) upconversion emissions associated to G14→H36 and F32→H36 transitions were observed and a significant higher in upconversion emission intensity is observed in core-shell nanorods. The effective decay time calculated are 230 and 110 μs for core-shell and doped nanorods, respectively, indicating the removal of surface defects due to surface coating. It reveals that the core-shell structure shows better upconversion emission efficiency.

Eu-Doped BaTiO3 Powder and Film from Sol-Gel Process with Polyvinylpyrrolidone Additive

Transparent BaTiO3:Eu3+ films were prepared via a sol-gel method and dip-coating technique, using barium acetate, titanium butoxide, and polyvinylpyrrolidone (PVP) as modifier viscosity. BaTiO3:Eu3+ films ~500 nm thick, crystallized after thermal treatment at 700 ºC. The powders revealed spherical and rod shape morphology. The optical quality of films showed a predominant band at 615 nm under 250 nm excitation. A preliminary luminescent test provided the properties of the Eu3+ doped BaTiO3.

Glucose detection using SERS with multi-branched gold nanostructures in aqueous medium

Gold nanoparticles (AuNPs), multi-branched gold nanoparticles (MBGNs), and silica-coated MBGNs (MBGNs-silica) were studied for rhodamine B (RB) and α-glucose detection at low concentration. The MBGNs SPR band in the NIR, which is tunable, is useful for SERS that was demonstrated using rhodamine B and α-glucose as probe molecules with detection limits of 50 pM and 5 mM (90 mg dL−1), respectively, much lower than that using regular AuNPs. The SERS signals of RB and α-glucose using MBGNs-silica are further enhanced with respect to AuNPs and MBGNs, which is attributed to the aggregation of the MBGNs and a stronger interaction. In the case of α-glucose, the functionalization process performed to both, α-glucose molecules and MBGNs, improves the interaction and allows measurements at low concentration.

Current improvement in hybrid quantum dot sensitized solar cells by increased light-scattering with a polymer layer

We investigate the effect of the incorporation of a material with efficient electron transport into a Hybrid Quantum Dot Sensitized Solar Cell (HyQDSSC). The performance of different quantum dot sensitized solar cells is compared with a cell containing poly [(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) with structure TiO2/PbS/PFN/CdS/ZnS. The photoconversion efficiency, as compared to our reference samples, was enhanced in some cases by approximately 45%, while the short-circuit current increased by up to 100% after the incorporation of PFN. The deposition order of the different components was crucial in achieving these improvements. Diffuse reflectance and impedance spectroscopy were used to study the behaviour of the cells. The observed enhancements are attributed to increased light scattering in the active layer, better charge transport, and a decrease in charge recombination and transport resistance.

Effect of solvent on the up- and downconversion emissions of Y 2 O 3 :Yb 3+ −Er 3+ nanofibers synthesized by a hydrothermal method

We report on the structural, morphological, and luminescent properties of Y2O3:Yb3+ (2%)–Er3+ (1%) nanofibers synthesized by a hydrothermal method as a function of the solvent composition ethanol/water. The average length and diameter of the nanofibers ranges from 1.1 to 2.3 μm, and from 50 to 110 nm, respectively. A cubic crystalline structure was obtained, and no effect of the solvent was observed. However, the increment of OHs, because of the increment of water, modifies the quality of the nanofibers. Such impurities improve the emission bands under 940 and 490 nm excitation, especially the red band, via multiphonon relaxation. Relaxation dynamics is explained, based on direct and back energy transfer, multiphonon relaxation, and cross-relaxation. The direct energy transfer coefficients (Cb2, Cb4, and Cb5) calculated by the proposed theoretical model point out the fact that upconverted emissions are notably favored by the increment of OHs. The energy backtransfer (C5b) and cross-relaxation (C51) coefficients depend only on the ion concentration and not on the OH content.

Improving the Optoelectronic Properties of Mesoporous TiO2 by Cobalt Doping for High-Performance Hysteresis-free Perovskite Solar Cells

We for the first time report the incorporation of cobalt into a mesoporous TiO2 electrode for application in perovskite solar cells (PSCs). The Co-doped PSC exhibits excellent optoelectronic properties; we explain the improvements by passivation of electronic trap or sub-band-gap states arising due to the oxygen vacancies in pristine TiO2, enabling faster electron transport and collection. A simple postannealing treatment is used to prepare the cobalt-doped mesoporous electrode; UV-visible spectroscopy, X-ray photoemission spectroscopy, space charge-limited current, photoluminescence, and electrochemical impedance measurements confirm the incorporation of cobalt, enhanced conductivity, and the passivation effect induced in the TiO2. An optimized doping concentration of 0.3 mol % results in the maximum power conversion efficiency of 18.16%, 21.7% higher than that of a similar cell with an undoped TiO2 electrode. Also, the device shows negligible hysteresis and higher stability, retaining 80.54% of the initial efficiency after 200 h.

Operating Mechanisms of Mesoscopic Perovskite Solar Cells through Impedance Spectroscopy and J–V Modeling

The performance of perovskite solar cell (PSC) is highly sensitive to deposition conditions, the substrate, humidity, and the efficiency of solvent extraction. However, the physical mechanism involved in the observed changes of efficiency with different deposition conditions has not been elucidated yet. In this work, PSCs were fabricated by the antisolvent deposition (AD) and recently proposed air-extraction antisolvent (AAD) process. Impedance analysis and J-V curve fitting were used to analyze the photogeneration, charge transportation, recombination, and leakage properties of PSCs. It can be elucidated that the improvement in morphology of perovskite film promoted by AAD method leads to increase in light absorption, reduction in recombination sites, and interstitial defects, thus enhancing the short-circuit current density, open-circuit voltage, and fill factor. This study will open up doors for further improvement of device and help in understanding its physical mechanism and its relation to the deposition methods.

Tunable white light from photo- and electroluminescence of ZnO nanoparticles

Tunable white light emission was obtained from ZnO nanorods with lengths ranging from 125 to 165 nm and quantum dots with an average size of 5 nm, synthesized with dodecylamine (DCA) as surfactant. It was possible to tailor the emission from cool to warm white light by changing the concentration of DCA in the synthesis process. The CIE coordinates for the white light obtained were (0.33, 0.32) in the case of photoluminescence and (0.31, 0.33) for electroluminescence from ZnO-based LEDs with a turn-on voltage of 4 and 6 V and a maximum current consumption of 2.32 mA at 10 V.

Labeling of HeLa cells using ZrO2:Yb3+-Er3+ nanoparticles with upconversion emission

Abstract. This work reports the synthesis, structural characterization, and optical properties of ZrO2:Yb3+-Er3+ (2–1 mol%) nanocrystals. The nanoparticles were coated with 3-aminopropyl triethoxysilane (APTES) and further modified with biomolecules, such as Biotin-Anti-rabbit (mouse IgG) and rabbit antibody-AntiKi-67, through a conjugation method. The conjugation was successfully confirmed by Fourier transform infrared, zeta potential, and dynamic light scattering. The internalization of the conjugated nanoparticles in human cervical cancer (HeLa) cells was followed by two-photon confocal microscopy. The ZrO2:Yb3+-Er3+ nanocrystals exhibited strong red emission under 970-nm excitation. Moreover, the luminescence change due to the addition of APTES molecules and biomolecules on the nanocrystals was also studied. These results demonstrate that ZrO2:Yb3+-Er3+ nanocrystals can be successfully functionalized with biomolecules to develop platforms for biolabeling and bioimaging.