Near-infrared Photon Upconversion Research Articles

Tailoring sensitization properties and improving near-infrared photon upconversion performance through alloying in superatomic molecular Au25 nanoclusters.

Noble-metal nanoclusters (NCs) protected by organic ligands have recently come to the forefront as potent triplet sensitizers for photon upconversion (UC) via triplet-triplet annihilation (TTA), owing to their capacity for atomic-level photophysical property customization. Among these, the rod-shaped bi-icosahedral [Au25(PPh3)10(S-C2H4Ph)5Cl2]2+ (Au-rod) NC is a particularly iconic superatomic molecular NC, recently identified as a near-infrared (NIR)-absorbing sensitizer for TTA-UC. In this study, we synthesized Cu-doped NCs, [Au25-xCux(PPh3)10(S-C2H4Ph)5Cl2]2+ (AuCu-rod), and paired them with 9,10-bis(phenylethynyl)anthracene (BPEA) annihilator/emitter to explore the impact of Cu-doping on the triplet sensitization and NIR-UC performance. The triplet state of AuCu-rod, with lifetime of 3 μs, exhibited a modest blue shift compared to the Au-rod, resulting in the increment in the driving force for triplet energy transfer (TET) to the BPEA acceptor. The TET rate constant was determined to be 5.0 × 107 M-1 s-1, which is an order of magnitude higher than the rate constant for the Au-rod/BPEA pair. This improvement has led to a remarkable increase in the TET efficiency. Notably, the AuCu-rod/BPEA pair facilitated the efficient UC of 805 nm NIR light into 510 nm visible light, realizing a large anti-Stokes shift close to 0.9 eV. The UC internal quantum yield of this combination was determined to be 2.33 ± 0.05%, marking a fivefold enhancement over the Au-rod sensitizer (0.49%). Thus, alloying NC sensitizers offers a promising route to enhance UC performance by tuning the triplet state energy and optimizing the compatibility between the sensitizer and annihilator. Additionally, in this series of experiments, the formation of small amounts of BPEA microaggregates was observed. These aggregates did not undergo singlet fission and could retain multiple long-lived triplet excitons. This characteristic facilitated TTA among triplet excitons, resulting in efficient NIR-to-visible UC emission.

Near-infrared photon upconversion and solar synthesis using lead-free nanocrystals

Near-infrared photon upconversion and solar synthesis using lead-free nanocrystals

Coherent all-optical steering of upconverted light by a nonlinear metasurface

In recent years a strong drive towards the miniaturization of nonlinear optics has been motivated by the functionalities it could empower in integrated devices. Among these, the upconversion of near-infrared photons to the visible and their manipulation is fundamental to downscale optical information. We propose a dual-beam scheme whereby a pulse at the telecom frequency ω (1550 nm wavelength) is mixed with its frequency-doubled replica at 2ω. When the two pump pulses are superimposed on a nonlinear, all-dielectric metasurface two coherent frequency-tripling pathways are excited: third-harmonic generation (THG, ω+ω+ω) and sum-frequency generation (SFG, ω+2ω). Their coherent superposition at 3ω produces interference, which we enable by filtering the k-space with the metasurface diffraction. The steering of the emission among diffraction orders, is sensitive to the relative phase between the two pumps. Therefore, by exploiting the phase as a tuning knob, the upconverted signal can be switched between diffraction orders with an efficiency >90%. The proposed approach can be envisioned as an all-optical method to reroute upconverted telecom photons.

Intense blue-emitting Yb/Tm-CaSiO3 wollastonite upconversion phosphors

Wollastonite is a naturally occurring mineral with a chemical formula of CaSiO3. Owing to outstanding mechanical, chemical, and thermal stabilities, wollastonites have become one of the most versatile industry minerals for applications in construction materials, cement, plastics, paints and coatings, friction, automobile brakes, ceramic and metallurgical applications to name a few. Despite technological importance, research on functional properties such as photon upconversion in wollastonites is still lacking. In this report, an initiative has been taken to demonstrate ultra-violet, blue, and near-infrared photon upconversion in CaSiO3 wollastonite via Yb and Tm doping. The wollastonite ceramics are synthesized via microwave hydrothermal technique followed up by heat-treatment in air. β-wollastonite (2M) phase in the synthesized samples has been confirmed by X-ray diffraction and a successful doping of Yb3+ and Tm3+ ions in the CaSiO3 lattice has been confirmed by X-ray photoelectron spectroscopy. The most intense phonon band has been observed at 872 cm−1. Upon 980 nm excitation, ultraviolet, intense blue, and near-infrared upconversion emissions as well as downshifting infrared emissions are observed from Tm3+ ions as a result of sensitization by Yb3+. The temporal evolution of the emitting states is studied to understand the emission mechanism. An absolute upconversion quantum yield of the 20Yb/0.5Tm–CaSiO3 sample in the 400–850 nm range is 0.79%.

Enhance the performance of dye-sensitized solar cells by constructing upconversion-core/semiconductor-shell structured NaYF4:Yb,Er @BiOCl microprisms

Upconversion spectral converters enable the utilization of infrared photons for dye-sensitized solar cells. However, the TiO2 photoanode photoelectron trapping loss caused by defects and ligands on upconversion material surface limits the dye-sensitized solar cells efficiency. Here, we separate spatially TiO2 particles and upconverters through crafting an uniform semiconductor BiOCl shell onto NaYF4:Yb3+,Er3+ upconverters surface by a hydrothermal method. Unlike common insulate SiO2 shells, the BiOCl shell decreases little the upconversion luminescence intensity from the upconversion core, but it can inhibit the photoelectron transfer from TiO2 to upconversion particles due to its higher conduction band position than that of TiO2, which eliminates the photoelectron trapping loss. In addition, the BiOCl shell can harvest 408 nm photons from upconversion cores to generate additional photoelectrons into TiO2 photoanode film. Consequently, the incorporation of upconversion-core/semiconductor-shell structured particles into TiO2 photoanodes of dye-sensitized solar cells achieves 29.8% increase of power conversion efficiency, whereas bare upconversion particles only get 11.9% increase as compared with dye-sensitized solar cells with pure TiO2 photoanodes. We quantify that among the relative efficiency increase by the incorporation of upconversion-core/semiconductor-shell particles: 17.2% from the reduced photoelectron trapping and the harvest of upconversion 408 nm photons by BiOCl shell, 4.9% from the green and red upconversion of near infrared photons, and 7.7% from the scattering effect of the designed spectral upconverters.

Triplet energy migration pathways from PbS quantum dots to surface-anchored polyacenes controlled by charge transfer.

Sensitization of molecular triplets using PbS quantum dots (QDs), followed by efficient triplet fusion, has been developed as a novel route to near-infrared-to-visible photon upconversion. Fundamentally, however, the mechanisms of triplet energy transfer (TET) from PbS QDs to surface-anchored polyacence acceptors remain highly debated. Here we study and side-by-side compare the kinetic pathways of TET from photoexcited PbS QDs to surface-anchored tetracene and pentacene derivatives using broad-band transient absorption spectroscopy spanning multiple decades of timescales. We find that the TET pathways are dictated by charge-transfer energetics at the QD/molecule interface. Charge transfer from QDs to tetracene was strongly endothermic, and hence spectroscopy showed one-step transformation from QD excited states to tetracene triplets in 302 ns. In contrast, hole transfer from QDs to pentacene was thermodynamically favoured and was confirmed by the formation of pentacene cation radicals in 13 ps, which subsequently evolved into pentacene triplets through a 101 ns electron transfer process. These results not only are consistent with a recently-established framework of charge-transfer-mediated TET, but also provide a route to manipulate triplet sensitization using lead-salt QDs for efficient upconversion of near-infrared photons.

Heavy Mn2+-doped near-infrared photon upconversion luminescence in fluoride RbZnF3:Yb3+,Mn2+ guided by dopant distribution simulation

NIR UC emission was observed in heavy Mn2+-doped RbZnF3:Yb3+,Mn2+ designed by the dopant-distribution prediction simulation. The GSA/ESA and GSA/ETU models of the super-exchange-coupled Yb3+–Mn2+–Mn2+ trimer are proposed for the NIR UC emission.

Hybridizing semiconductor nanocrystals with metal-organic frameworks for visible and near-infrared photon upconversion.

Hybrid materials consisting of semiconductor nanocrystals and metal-organic frameworks (MOFs) were prepared for the first time to achieve photon upconversion based on triplet-triplet annihilation (TTA-UC) in the solid-state, which allowed TTA-UC with large anti-Stokes shifts in the visible and near-infrared regions.

Publisher's Note: “Topology optimized gold nanostrips for enhanced near-infrared photon upconversion” [Appl. Phys. Lett. 111, 133102 (2017)

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Topology optimized gold nanostrips for enhanced near-infrared photon upconversion

This letter presents a topology optimization study of metal nanostructures optimized for electric-field enhancement in the infrared spectrum. Coupling of such nanostructures with suitable ions allows for an increased photon-upconversion yield, with one application being an increased solar-cell efficiency by exploiting the long-wavelength part of the solar spectrum. In this work, topology optimization is used to design a periodic array of two-dimensional gold nanostrips for electric-field enhancements in a thin film doped with upconverting erbium ions. The infrared absorption band of erbium is utilized by simultaneously optimizing for two polarizations, up to three wavelengths, and three incident angles. Geometric robustness towards manufacturing variations is implemented considering three different design realizations simultaneously in the optimization. The polarization-averaged field enhancement for each design is evaluated over an 80 nm wavelength range and a ±15-degree incident angle span. The highest polarization-averaged field enhancement is 42.2 varying by maximally 2% under ±5 nm near-uniform design perturbations at three different wavelengths (1480 nm, 1520 nm, and 1560 nm). The proposed method is generally applicable to many optical systems and is therefore not limited to enhancing photon upconversion.

Ligand enhanced upconversion of near-infrared photons with nanocrystal light absorbers.

We designed and synthesized a tetracene derivative 4-(tetracen-5-yl)benzoic acid (CPT) as a transmitter ligand used in PbS/PbSe nanocrystal (NC) sensitized upconversion of near infrared (NIR) photons. Under optimal conditions, comparing CPT functionalized NCs with unfunctionalized NCs as sensitizers, the upconversion quantum yield (QY) was enhanced 81 times for 2.9 nm PbS NCs from 0.021% to 1.7%, and 11 times for 2.5 nm PbSe NCs from 0.20% to 2.1%. The surface density of CPT controls the solubility of functionalized NCs and the upconversion QY. By increasing the concentration of CPT in the ligand exchange solution, the number of CPT ligand per NC increases. The upconversion QY is maximized at a transmitter density of 1.2 nm-2 for 2.9 nm PbS, and 0.32 nm-2 for 2.5 nm PbSe. Additional transmitter ligands inhibit photon upconversion due to triplet-triplet annihilation (TTA) between two neighboring CPT molecules on the NC surface. 2.1% is the highest reported QY for TTA-based photon upconversion in the NIR with the use of earth-abundant materials.

Metallonaphthalocyanines as triplet sensitizers for near-infrared photon upconversion beyond 850 nm

In triplet-triplet annihilation-based photon upconversion (TTA-UC), the utilization of near-infrared (NIR) light with a wavelength longer than 850 nm remains an outstanding issue. We realized this by employing metallonaphthalocyanines as triplet sensitizers; upon excitation of NIR light (856 nm), upconverted emission was observed in the visible range with remarkable photostability.

Green, red and near-infrared photon up-conversion in Ga–Ge–Sb–S:Er3+ amorphous chalcogenides

We report on compositional tuning in Er3+ ions doped Ga–Ge–Sb–S glassy system allowing for effective 2H11/2→4I15/2 (530nm), 4S3/2→4I15/2 (550nm), 4F9/2→4I15/2 (660nm), 4I9/2→4I15/2 (810nm), 4I11/2→4I15/2 (990nm) intra-4f electronic transition emissions of Er3+ ions under 808nm, 980nm or 1550nm laser pumping. We changed the composition of well-known Ge20Ga5Sb10S65 glass to Ge25Ga10−xSbxS65, where x=0.5at%, 2.5at% or 5.0at% and doped it with 0.5at% of Er3+ ions. The short-wavelength absorption edge of the studied glassy hosts is blue-shifted by substitution of Sb with Ga to ~500nm making the green emission at 530nm and 550nm and even 495nm (4F7/2→4I15/2) observable, while the glass stability was kept high characterized with the difference of Tc−Tg>100K and mean coordination numbers 2.67–2.71. Up-conversion emission decay times of all anti-Stokes emissions were in the range of 0.2–2.1ms. The influence of Ga substitution with Sb on the structure and the optical properties was investigated. The spectroscopic parameters for Er3+ ions with local environment change were analyzed based on Judd–Ofelt theory.

Carbon quantum dots serving as spectral converters through broadband upconversion of near-infrared photons for photoelectrochemical hydrogen generation

Carbon quantum dots with photoluminescence (PL) upconversion properties were used as spectral converters through near-infrared photon harvesting and conversion for CdSe sensitized TiO2 nanorod array photoanodes.

Broadband dye-sensitized upconversion of near-infrared light

Photon upconversion of near-infrared photons is a promising way to overcome the Shockley–Queisser efficiency limit of 32% of a single-junction solar cell. However, the practical applicability of the most efficient known upconversion materials at moderate light intensities is limited by their extremely weak and narrowband near-infrared absorption. Here, we introduce the concept of an upconversion material where an organic near-infrared dye is used as an antenna for the β-NaYF4:Yb,Er nanoparticles in which the upconversion occurs. The overall upconversion by the dye-sensitized nanoparticles is dramatically enhanced (by a factor of ∼3,300) as a result of increased absorptivity and overall broadening of the absorption spectrum of the upconverter. The proposed concept can be extended to cover any part of the solar spectrum by using a set of dye molecules with overlapping absorption spectra acting as an extremely broadband antenna system, connected to suitable upconverters. Researchers demonstrate an approach for upconverting near-infrared light in solar cells using an organic dye as an antenna for nanoparticles. Increased absorptivity and overall broadening of the upconverter's absorption spectrum enhance the upconversion process by a factor of around 3,300.

Modeling upconversion of erbium doped microcrystals based on experimentally determined Einstein coefficients

The upconversion of infrared photons is a promising possibility to enhance solar cell efficiency by producing electricity from otherwise unused sub-band-gap photons. We present a rate equation model and the relevant processes in order to describe the upconversion of near-infrared photons. The model considers stimulated and spontaneous processes, multi-phonon relaxation, and energy transfer between neighboring ions. The input parameters for the model are experimentally determined for the material system, β-NaEr0.2Y0.8F4. The determination of the transition probabilities, also known as the Einstein coefficients, is the focus of the parameterization. The influence of multi-phonon relaxation and energy transfer on the upconversion are evaluated and discussed in detail. Since upconversion is a non-linear process, the irradiance dependence of the simulations is investigated and compared to the experimental data of quantum efficiency measurements. The results are very promising and indicate that upconversion is reasonably physically described by the rate equations. Therefore, the presented model will be the basis for further simulations concerning various applications of upconversion, such as in combination with plasmon resonances in metal nanoparticles.

Spectroscopic characterization and up-conversion in sol–gel derived Yb 3+–Pr 3+ co-doped SiO 2–LaF 3 nano-glass-ceramics

The up-conversion of near infrared photons into the visible range is of major interest for lighting appliances and photonic integrated devices. Here we report up-conversion luminescence in transparent nano-glass-ceramics with composition of 95SiO 2–5LaF 3 co-doped with 0.1 mol% of Pr 3+ and 0.3 mol% of Yb 3+, which were synthesized by different thermal treatments of precursor sol–gel glasses. Precipitation of LaF 3 nanocrystals during ceramming process was confirmed by means of X-ray diffraction and the partition of rare-earth ions into them has been analyzed. The effect of increasing thermal treatment temperature and adding Yb 3+ ions in the degree of crystallinity of the samples has been discussed. Efficient up-conversion emissions were observed under infrared excitation of the Yb 3+ ions in the co-doped Yb 3+–Pr 3+ samples, while it was hardly detected in single Pr 3 +-doped samples.

Near-infrared photon upconversion devices based on GaNAsSb active layer lattice matched to GaAs

Room-temperature full GaAs-based near-infrared (NIR) upconversion has been demonstrated by connecting lattice-matched GaNAsSb/GaAs p-i-n photodetectors in series with commercial GaAs/AlGaAs light-emitting diodes (LEDs). Due to the avalanche gain in GaNAsSb/GaAs photodetectors and high internal efficiency in GaAs/AlGaAs LEDs, the upconversion efficiency of the integrated system reaches 0.048 W/W under −7 V bias, much higher than any existing NIR upconverters without amplifying structures. We have further investigated the dependence of the upconversion efficiency on applied bias and incident light intensity. The present work establishes an experimental base for direct epitaxial growth of full GaAs-based NIR upconverters with high upconversion efficiencies.