Jose Marques-Hueso

Optimizing infrared to near infrared upconversion quantum yield of β-NaYF4:Er3+ in fluoropolymer matrix for photovoltaic devices

The present study reports for the first time the optimization of the infrared (1523 nm) to near-infrared (980 nm) upconversion quantum yield (UC-QY) of hexagonal trivalent erbium doped sodium yttrium fluoride (β-NaYF4:Er3+) in a perfluorocyclobutane (PFCB) host matrix under monochromatic excitation. Maximum internal and external UC-QYs of 8.4% ± 0.8% and 6.5% ± 0.7%, respectively, have been achieved for 1523 nm excitation of 970 ± 43 Wm−2 for an optimum Er3+ concentration of 25 mol% and a phosphor concentration of 84.9 w/w% in the matrix. These results correspond to normalized internal and external efficiencies of 0.86 ± 0.12 cm2 W−1 and 0.67 ± 0.10 cm2 W−1, respectively. These are the highest values ever reported for β-NaYF4:Er3+ under monochromatic excitation. The special characteristics of both the UC phosphor β-NaYF4:Er3+ and the PFCB matrix give rise to this outstanding property. Detailed power and time dependent luminescence measurements reveal energy transfer upconversion as the dominant UC mechanism.

Ultra-high photoluminescent quantum yield of β-NaYF4: 10% Er3+ via broadband excitation of upconversion for photovoltaic devices.

The upconversion photoluminescent quantum yield (PLQY) of erbium-doped hexagonal sodium yttrium fluoride (β-NaYF(4): 10% Er(3+) was measured under broadband excitation with full width half maxima ranging from 12 to 80 nm. A novel method was developed to increase the bandwidth of excitation, while remaining independent of power via normalization to the air mass 1.5 direct solar spectrum. The measurements reveal that by broadening the excitation spectrum a higher PLQY can be achieved at lower solar concentrations. The highest PLQY of 16.2 ± 0.5% was achieved at 2270 ± 100 mW mm(-2) and is the highest ever measured.

Electronic structure, optical properties, and lattice dynamics in atomically thin indium selenide flakes

The progressive stacking of chalcogenide single layers gives rise to two-dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet the properties of some members of the chalcogenide family remain unexplored. Indium selenide (InSe) is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. Here, we reveal the lattice dynamics, optical and electronic properties of atomically thin InSe flakes prepared by micromechanical cleavage. Raman active modes stiffen or soften in the flakes depending on which electronic bonds are excited. A progressive blue-shift of the photoluminescence peaks is observed for decreasing flake thickness (as large as 0.2 eV for three single layers). First-principles calculations predict an even larger increase in the bandgap, 0.40 eV, for three single layers, and as much as 1.1 eV for a single layer. These results are promising from the point of view of the versatility of this material for optoelectronic applications at the nanometer scale and compatible with Si and III-V technologies.

High-resolution electron-beam patternable nanocomposite containing metal nanoparticles for plasmonics

Polymer nanocomposites containing noble metal nanoparticles are promising materials for plasmonic applications. In this paper, we report on a high-resolution negative-tone nanocomposite resist based on poly(vinyl alcohol) where silver nanoparticles and nanopatterns are simultaneously generated by electron-beam lithography. Our results indicate nanostructures with a relatively high concentration of nanoparticles and, consequently, an electromagnetic coupling among the nanoparticles. Therefore, the patternable nanocomposite described in this work may be a suitable material for future plasmonic circuitry.

Improving Optical Temperature Sensing Performance of Er 3+ Doped Y 2 O 3 Microtubes via Co-doping and Controlling Excitation Power

This work presents a new method to effectively improve the optical temperature behavior of Er3+ doped Y2O3 microtubes by co-doping of Tm3+ or Ho3+ ion and controlling excitation power. The influence of Tm3+ or Ho3+ ion on optical temperature behavior of Y2O3:Er3+ microtubes is investigated by analyzing the temperature and excitation power dependent emission spectra, thermal quenching ratios, fluorescence intensity ratios, and sensitivity. It is found that the thermal quenching of Y2O3:Er3+ microtubes is inhibited by co-doping with Tm3+ or Ho3+ ion, moreover the maximum sensitivity value based on the thermal coupled 4S3/2/2H11/2 levels is enhanced greatly and shifts to the high temperature range, while the maximum sensitivity based on 4F9/2(1)/4F9/2(2) levels shifts to the low temperature range and greatly increases. The sensitivity values are dependent on the excitation power, and reach two maximum values of 0.0529/K at 24 K and 0.0057/K at 457 K for the Y2O3:1%Er3+, 0.5%Ho3+ at 121 mW/mm2 excitation power, which makes optical temperature measurement in wide temperature range possible. The mechanism of changing the sensitivity upon different excitation densities is discussed.

Optical properties of different polymer thin films containing in situ synthesized Ag and Au nanoparticles

Here we report on the in situ synthesis of Ag and Au nanoparticles inside several polymer matrixes by solid-state chemical reduction of a metallic salt. Poly(ethyleneimine) (PEI), poly(hydroxyethyl methacrylate) (PHEMA), poly(vinylpyrrolidone) (PVP), novolak, poly(4-vinylphenol) (P4VP), poly(4-vinylphenol)-co-(methyl methacrylate) (P4VP-co-MMA) and poly(styrene-co-allyl alcohol) (PS-co-AA) were able to reduce Ag(I) and Au(III) to the corresponding nanoparticles during the baking process. The nanoparticle diameters of Ag and Au were found to range from 2 to 25 nm. TEM also indicated a uniform distribution of nanoparticles embedded in the thin film. This approach is suitable for controlling the size of the nanoparticles and its homogeneous distribution in the polymer matrix.

Enhanced up-conversion for photovoltaics via concentrating integrated optics

Concentrating optics are integrated into up-conversion photovoltaic (UC-PV) devices to independently concentrate sub-band-gap photons on the up-conversion layer, without affecting the full solar concentration on the overlying solar cell. The UC-PV devices consist of silicon solar cells optimized for up-conversion, coupled with tapered and parabolic dielectric concentrators, and hexagonal sodium yttrium fluoride (β-NaYF₄) up-converter doped with 25% trivalent erbium (Er³⁺). A normalized external quantum efficiency of 1.75x10⁻² cm²/W and 3.38x10⁻² cm²/W was obtained for the UC-PV device utilizing tapered and parabolic concentrators respectively. Although low to moderate concentration was shown to maximize UC, higher concentration lead to saturation and reduced external quantum efficiency. The presented work highlights some of the implications associated with the development of UC-PV devices and designates a substantial step for integration in concentrating PV.

Ag and Au/DNQ-novolac nanocomposites patternable by ultraviolet lithography: a fast route to plasmonic sensor microfabrication

In this work we report on a method to synthesize Ag–Au nanoparticles/polymer nanocomposite patterns by UV lithography. The photoresists are based on DNQ-novolac as the polymer matrix, and Ag(I) and Au(III) salts as the nanoparticle precursors. After UV lithography, silver and gold nanoparticles are in situ synthesized inside the polymer patterns during a post bake. The resulting structured nanocomposite shows a characteristic absorbance spectrum related to the plasmon frequency of the synthesized noble metal NPs. This method represents a fast, simple and low-cost approach to the formation of extended polymer patterns with embedded silver or gold NPs. Moreover, it is a mechanism to position nanometric particles with micrometric resolution, which represents a useful tool for nanoscience. Furthermore, even with the polymeric cover, NPs plasmon resonance is affected by the binding of some organic molecules. This concept has been proven with 2-mercaptoethanol molecules, which demonstrates the feasibility of localized surface plasmon resonance chemo/biosensors by using the proposed technology.

Au-PVA Nanocomposite Negative Resist for One-Step Three-Dimensional e-Beam Lithography

Au nanoparticles are synthesized in situ upon the electron beam exposure of a poly(vinyl alcohol) (PVA) thin film containing Au(III). The e-beam-irradiated areas are insoluble in water (negative-tone resist), and Au-PVA nanocomposite patterns with a variable profile along the structure can be thus generated (3D lithography) in a single step. A local characterization of the generated patterns is performed by high-resolution transmission electron microscopy and UV-vis localized surface plasmon resonance microspectroscopy. This characterization confirms the presence of crystalline nanoparticles and aggregates.

Self-absorption in upconverter luminescent layers: impact on quantum yield measurements and on designing optimized photovoltaic devices

This Letter details a theoretical investigation of self-absorption within an upconverter (UC) material, consisting of trivalent erbium (Er3+)-doped hexagonal sodium yttrium fluoride (β-NaYF4) and its implications on two experimental situations: the case of a quantum yield measurement, and on the effective performance in a UC-enhanced photovoltaic (PV) device. The study demonstrates that an optimization of the thickness is essential in order to reduce the effect of self-absorption and maximize the possible additional photocurrent that could be harvested. It also has been found that the external photoluminescence quantum yield (ePLQY) measured through an integrating sphere may result in an underestimation with respect to the performance that the UC material could achieve in a UC-PV device. Finally, it has been found the optimal thickness and the molar concentration of Er3+ ions are inversely proportional, suggesting that an optimal number (1.3-2.9·10(17)) of Er3+ ions should be contained within the UC layer.