Up-converted Energy Research Articles

Frequency up-converted piezoelectric energy harvester for ultralow-frequency and ultrawide-frequency-range operation

At present, frequency up-converted piezoelectric energy harvesters are disadvantaged by their narrow range of operating frequencies and low efficiency at ultralow-frequency excitation. To address these shortcomings, we propose herein an impact-driven frequency up-converted piezoelectric energy harvester composed of two driving beams and a generating beam. We find experimentally that the proposed device offers efficient energy output over an ultrawide-frequency-range and performs very well in the ultralow-frequency excitation. A maximum peak power of 29.3 mW is achieved under 0.5g acceleration at the excitation frequency of 12.7 Hz. The performance of the energy harvester can be adjusted and optimized by adjusting the spacing between the driving and generating beams. The results show that the proposed harvester has the potential to power miniaturized portable devices and wireless sensor nodes.

New Triplet Sensitization Routes for Photon Upconversion: Thermally Activated Delayed Fluorescence Molecules, Inorganic Nanocrystals, and Singlet-to-Triplet Absorption.

Photon upconversion based on triplet-triplet annihilation (TTA-UC) has attracted much interest because of its possible applications to renewable energy production and biological fields. In particular, the UC of near-infrared (NIR) light to visible (vis) light is imperative to overcome the Shockley-Queisser limit of single-junction photovoltaic cells, and the efficiency of photocatalytic hydrogen production from water can also be improved with the aid of vis-to-ultraviolet (UV) UC. However, both processes have met limitations in the wavelength range, efficiency, and sensitivity for weak incident light. This Account describes recent breakthroughs that solve these major problems, new triplet sensitization routes to significantly enlarge the range of conversion wavelength by minimizing the energy loss during intersystem crossing (ISC) of triplet sensitizers or bypassing the ISC process. The photochemical processes of TTA-UC in general start with the absorption of longer wavelength incident light by triplet sensitizers, which generate the triplet states via ISC. This ISC inevitably accompanies the energy loss of hundreds of millielectronvolts, which significantly limits the TTA-UC with large anti-Stokes shifts. The small S1-T1 gap of molecules showing thermally activated delayed fluorescence (TADF) allows the sensitization of emitters with the highest T1 and S1 energy levels ever employed in TTA-UC, which results in efficient vis-to-UV UC. As alternatives to molecular sensitizers in the NIR region, inorganic nanocrystals with broad NIR absorption bands have recently been shown to work as effective sensitizers for NIR-to-vis TTA-UC. Their small exchange splitting minimizes the energy loss during triplet sensitization. The modification of nanocrystal surfaces with organic acceptors via coordination bonds allows efficient energy transfer between the components and succeeding TTA processes. To remove restrictions on the energy loss during ISC, molecules with direct singlet-to-triplet (S-T) excitation are employed as triplet sensitizers. Although the S-T absorption is spin forbidden, large spin-orbital coupling occurs for appropriately designed metal complexes, which allow S-T absorption in the NIR region with large absorption coefficients. While the triplet lifetime of such S-T absorption sensitizers is often short (less than microsecond), the integration of the molecular sensitizers with emitter assemblies allows facile Dexter energy transfer to the surrounding emitter molecules, leading to efficient NIR-to-vis UC emission through triplet energy migration (TEM) in the condensed state. By judicious modification of the chromophore structures, the first example of NIR-to-blue UC has also been achieved. It is essential to combine these new triplet sensitization routes with an upconverted energy collection (UPCON) approach in molecular assemblies to effectively populate emitter triplets and to overcome remaining issues including back energy transfer. We propose two overall materials designs for the TEM-UPCON strategy, core-shell-shell structures and trilayer structures composed of triplet donor, acceptor, and energy collector. The fusion between triplet science and chemistry of self-assembly would overcome previous difficulties of NIR-to-vis and vis-to-UV TTA-UC toward real-world applications ranging from energy to biology.

Near-Infrared Triggered Upconversion Polymeric Nanoparticles Based on Aggregation-Induced Emission and Mitochondria Targeting for Photodynamic Cancer Therapy.

Photodynamic therapy (PDT) is an auspicious strategy for cancer therapy by yielding reactive oxygen species (ROS) under light irradiation. Here, we have developed near-infrared (NIR) triggered polymer encapsulated upconversion nanoparticles (UCNPs) based on aggregation-induced emission (AIE) characteristics and mitochondria target ability for PDT. The coated AIE polymer as a photosensitizer can be photoactivated by the up-converted energy of UCNPs upon 980 nm laser irradiation, which could generate ROS efficiently in mitochondria and induce cell apoptosis. Moreover, a "sheddable" poly(ethylene glycol) (PEG) layer was easily conjugated at the surface of NPs. The pH-responsive PEG layer shields the surface positive charges and shows stronger protein-resistance ability. In the acidic tumor environment, PEGylated NPs lose the PEG layer and show the mitochondria-targeting ability by responding to tumor acidity. A cytotoxicity study indicated that these NPs have good biocompatibility in the dark but exert severe cytotoxicity to cancer cells, with only 10% cell viability, upon being irradiated with an NIR laser. The AIE nanoparticles are a good candidate for effective mitochondria targeting photosensitizer for PDT.

Retraction of "Preorganized Chromophores Facilitate Triplet Energy Migration, Annihilation and Upconverted Singlet Energy Collection".

Photon upconversion (UC) based on triplet–triplet annihilation (TTA) has the potential to enhance significantly photovoltaic and photocatalytic efficiencies by harnessing sub-bandgap photons, but the progress of this field is held back by the chemistry problem of how to preorganize multiple chromophores for efficient UC under weak solar irradiance. Recently, the first maximization of UC quantum yield at solar irradiance was achieved using fast triplet energy migration (TEM) in metal–organic frameworks (MOFs) with ordered acceptor arrays, but at the same time, a trade-off between fast TEM and high fluorescence efficiency was also found. Here, we provide a solution for this trade-off issue by developing a new strategy, triplet energy migration, annihilation and upconverted singlet energy collection (TEM–UPCON). The porous structure of acceptor-based MOF crystals allows triplet donor molecules to be accommodated without aggregation. The surface of donor-doped MOF nanocrystals is modified with highly fluoresc...

Up-conversion luminescence in Yb3+-Er3+/Tm3+ co-doped Al2O3-TiO2 nano-composites

The sol gel method was used to prepare rare-earths (Yb3+-Er3+ and Yb3+-Tm3+) co-doped Al2O3-TiO2 nano-composite powder phosphors and their up-conversion luminescence properties were investigated. Mixed oxides of titania (TiO2) rutile phase and an early stage crystallization of alumina (Al2O3) phase were confirmed from the X-ray diffraction data with the average crystallite size of ∼36nm. The rutile phase TiO2 was further confirmed by selected area diffraction analysis of the composites. Microscopy analysis showed interesting rod-like morphologies with rough surfaces indicating that a spherulitic growth process took place during the crystal growth. Photoluminescence characterization of the phosphors was carried out under near infra-red excitation at 980nm and the prominent emission bands were observed in the visible region at 523, 548 and 658nm for the Yb3+-Er3+ co-doped systems. Emission in bands extending from the visible to near infra-red regions were observed at 480, 650, 693 and 800nm for the Yb3+-Tm3+ co-doped systems. These upconverted emissions and energy transfer mechanisms taking place are discussed in detail.

Preorganized Chromophores Facilitate Triplet Energy Migration, Annihilation and Upconverted Singlet Energy Collection.

Photon upconversion (UC) based on triplet-triplet annihilation (TTA) has the potential to enhance significantly photovoltaic and photocatalytic efficiencies by harnessing sub-bandgap photons, but the progress of this field is held back by the chemistry problem of how to preorganize multiple chromophores for efficient UC under weak solar irradiance. Recently, the first maximization of UC quantum yield at solar irradiance was achieved using fast triplet energy migration (TEM) in metal-organic frameworks (MOFs) with ordered acceptor arrays, but at the same time, a trade-off between fast TEM and high fluorescence efficiency was also found. Here, we provide a solution for this trade-off issue by developing a new strategy, triplet energy migration, annihilation and upconverted singlet energy collection (TEM-UPCON). The porous structure of acceptor-based MOF crystals allows triplet donor molecules to be accommodated without aggregation. The surface of donor-doped MOF nanocrystals is modified with highly fluorescent energy collectors through coordination bond formation. Thanks to the higher fluorescence quantum yield of surface-bound collectors than parent MOFs, the implementation of the energy collector greatly improves the total UC quantum yield. The UC quantum yield maximization behavior at ultralow excitation intensity was retained because the TTA events take place only in the MOF acceptors. The TEM-UPCON concept may be generalized to collectors with various functions and would lead to quantitative harvesting of upconverted energy, which is difficult to achieve in common molecular diffusion-based systems.

Design and experiment of a human-limb driven, frequency up-converted electromagnetic energy harvester

We present a frequency up-converted electromagnetic energy harvester that generates significant power from human-limb motion (hand-shaking). Because the power generated by a vibration energy harvester is proportional to the operating frequency, the proposed energy harvester has been designed to up-convert the applied low-frequency vibration to a high-frequency vibration by mechanical impact. Upon excitation, a freely moveable ball (non-magnetic) within a cylindrical structure periodically hits two magnets suspended on two helical compression springs located at either ends of the cylinder, allowing these to vibrate with higher frequencies. The relative motion between the magnets and coils (wrapped around the outside of the cylinder) induces e.m.f. (voltage). High-frequency oscillators have been designed through the design parameters (i.e., frequency, spring stiffness, mechanical, and electrical damping), to minimize the power loss. A prototype was fabricated and tested both using a vibration exciter and by manual hand-shaking. The fabricated device showed non-resonant behavior during the vibration exciter test. At optimum load condition, the frequency up-converted generators (FUGs) delivered 0.84mW and 0.96mW of average power. A maximum 2.15mW of average power was obtained from the device with series connected FUGs while it was mounted on a smart phone and was hand-shaken. The fabricated device exhibited 0.33mWcm−3 of average power density, which is very high compared to the current state-of-the-art devices, indicating its ability in powering portable and wearable smart devices from extremely low frequency (∼5Hz) vibration.

Efficient Triplet-Triplet Annihilation-Based Upconversion for Nanoparticle Phototargeting.

High-efficiency upconverted light would be a desirable stimulus for triggered drug delivery. Here we present a general strategy to achieve photoreactions based on triplet-triplet annihilation upconversion (TTA-UC) and Förster resonance energy transfer (FRET). We designed PLA-PEG micellar nanoparticles containing in their cores hydrophobic photosensitizer and annihilator molecules which, when stimulated with green light, would undergo TTA-UC. The upconverted energy was then transferred by FRET to a hydrophobic photocleavable group (DEACM), also in the core. The DEACM was bonded to (and thus inactivated) the cell-binding peptide cyclo-(RGDfK), which was bound to the PLA-PEG chain. Cleavage of DEACM by FRET reactivated the PLA-PEG-bound peptide and allowed it to move from the particle core to the surface. TTA-UC followed by FRET allowed photocontrolled binding of cell adhesion with green light LED irradiation at low irradiance for short periods. These are attractive properties in phototriggered systems.

A Three-Axial Frequency-Tunable Piezoelectric Energy Harvester Using a Magnetic-Force Configuration

To date, researchers have utilized energy harvesters to power wireless sensor nodes as self-powered wireless sensors to create many innovative wireless sensors network applications such as medical monitoring, machining-condition monitoring, and structural-health monitoring. Regarding to energy harvesters, some researchers demonstrated wideband or frequency up-converted vibrational energy harvesters using magnetic force together with piezoelectric materials. However, these harvesters are not able to harness 3-D or three-axial mechanical energy through using one single mechanism or configuration. To address this problem, we report a novel magnetic-force-configured three-axial frequency-tunable piezoelectric energy harvester in this paper. Due to the magnetic-force configuration, the harvester converts ambient three-axial mechanical vibration/motion to piezoelectric voltage-response (i.e., three-axial energy harvesting). Simultaneously, the harvester also converts the ambient vibration/motion at a lower frequency to higher frequency without mechanical wear-out (i.e., noncontact frequency up-conversion). Through modifying the configuration, the oscillating frequency is tunable. By frequency tuning, the harvester's oscillating frequency and ambient vibration frequency are able to be matched to maximize the power output. Experimental results show the peak voltage, peak power, and frequency conversion of one single piezoelectric beam of the harvester under an in-plane and out-of-plane vibration is up to 800 mV, 640 nW, and from 7 to 56 Hz, and 27 mV, 729 pW, and from 1 to 294 Hz, respectively. These results confirm the harvester is capable of harnessing energy from 3-D and three-axial mechanical motion/vibration, addressing frequency-mismatching issue, avoiding mechanical wear-out problems, and producing a stable voltage output. Due to these, the energy-harvesting approach will enable more novel and practical wireless sensors network applications in the future.

Conductive upconversion Er,Yb-FTO nanoparticle coating to replace Pt as a low-cost and high-performance counter electrode for dye-sensitized solar cells.

F-doped SnO2 (FTO) nanocrystals modified by Er and Yb with upconversion capability and excellent catalytic properties have been designed and fabricated as an economic replacement for Pt for use as the counter electrode (CE) in dye-sensitized solar cells. The cost of the UC-FTO counter electrode is only ∼(1)/20th of that for Pt. The upconverted luminescence-mediated energy transfer and the superior catalytic property for I3(-)/I(-) circulation overpowered the slight degradation caused by increased CE/electrolyte interface resistance. A 23.9% enhancement in photocurrent was achieved with little degradation in photovoltage, resulting in a 9.12% increase in solar-to-electric power conversion efficiency. Near-infrared (NIR) light-to-electricity has been directly observed by SPS and IPCE characterizations, showing the effect of the upconversion counter electrode.

A non-resonant, frequency up-converted electromagnetic energy harvester from human-body-induced vibration for hand-held smart system applications

We present a non-resonant, frequency up-converted electromagnetic energy harvester that generates significant power from human-body-induced vibration, e.g., hand-shaking. Upon excitation, a freely movable non-magnetic ball within a cylinder periodically hits two magnets suspended on two helical compression springs located at either ends of the cylinder, allowing those to vibrate with higher frequencies. The device parameters have been designed based on the characteristics of human hand-shaking vibration. A prototype has been developed and tested both by vibration exciter (for non-resonance test) and by manual hand-shaking. The fabricated device generated 110 μW average power with 15.4 μW cm−3 average power density, while the energy harvester was mounted on a smart phone and was hand-shaken, indicating its ability in powering portable hand-held smart devices from low frequency (<5 Hz) vibrations.

Theoretical modeling and analysis of mechanical impact driven and frequency up-converted piezoelectric energy harvester for low-frequency and wide-bandwidth operation

Vibration energy harvesters are capable of generating significant amount of power at higher frequencies rather than generating at low frequencies. Moreover, as low frequency vibrations (1–30Hz) around the ambient environment are discursive in nature, resonance based power generators are limited to use within this low frequency range. In this paper, a mechanical impact driven and frequency up-converted wide-bandwidth piezoelectric vibration energy harvester has been proposed and demonstrated theoretically and experimentally. It converts low frequency environmental vibrations into high frequency vibration by mechanical impact. A low frequency flexible driving beam with horizontally extended tip mass, upon excitation, hits two high frequency rigid piezoelectric generating beams at the same time causing a change in the driving beam's effective stiffness that allows the device to offer approximately 180% increased −3dB bandwidth and more than 62% of the maximum power generation within the remaining operating frequency range as well. The overall bandwidth is 7.5Hz within 7–14.5Hz frequency range generating a minimum peak power of 233μW. A maximum of 378μW peak power from one generating beam is achieved under 6ms−2 acceleration at the resonant frequency of 14.5Hz. Output of both generating beams connected in series produces 734μW peak power under the same operating condition with the corresponding power density 38.8μWcm−3. The experimental results show some discrepancy with the theoretical results due to mechanical loss during impact and the process variations in the beam formation and assembling. The theoretical and experimental results reveal that the proposed configuration has the potential of powering small portable, handheld wireless smart devices from low frequency, specially human motion related vibrations.

Communication: Trapping upconverted energy in neat platinum porphyrin films via an unexpected fusion mechanism

Direct observation of an unexpected product from excited state fusion of two excited triplet states in platinum octaethylporphyrin is reported. Transient spectroscopy was used to identify the product as a metal centered (d, d) state that decays slowly compared with the rate of fusion. The reaction was demonstrated to be second order with a rate coefficient of k(TTF) = (5.4 ± 0.4) × 10(-10) cm(3) · s(-1). The results contrast with the common assumption that fusion proceeds directly to annihilation via rapid non-radiative deactivation of the products. Following visible photo-excitation, the fusion process results in energetic upconversion of the incident photons stored in the higher energy (d, d) state at irradiances below the threshold for multi-photon absorption.

Size dependent luminescence properties of Er3+ doped nano-crystalline Y2O3

Er3+ doped Y2O3 nano-crystals with different size are prepared using combustion method. Size effect on luminescence properties of Er3+ doped Y2O3 nano crystals are investigated. No shift of the absorption peak in the photo-acoustic spectra is observed with the decrease of the Y2O3particle size, indicating that the size induced energy shifts of the rare-earth levels are negligible. However, the emission spectra under 488nm excitation indicate that the ratio of the intensity of 4S3/2→4I15/2 transition to that of 2H11/2→4I15/2 decreases with the decrease of the particle size. It is believed that the rate of hypersensitive transition of 2H11/2→4I15/2 increases with the decrease of the particle size more quickly than that of transition of 4S3/2→4I15/2. The time dependence of the 554nm luminescence decay excited by 518nm reveals that the rate of up-converted energy transfer occurring between two Er3+ ions in 4S3/2 state increases with the decrease of the particle size.

Two-photon-pumped frequency-upconverted yellow lasing in a novel dye solution

Two-photon induced frequency upconversion emission and two-photon-pumped (TPP) lasing properties of a novel dye, trans-2-[p-(N-ethyl-N-(hydroxyethyl)amino)styryl]-N-methylthiazolinium iodide (1) were investigated. This dye exhibits excellent TPP lasing at ∼577 nm when it is pumped with a 1064 nm pulsed laser beam. The net conversion efficiency from the absorbed 1064 nm pump energy to the ∼577 nm upconverted lasing energy was measured to be ∼2.2%.

LASING PROPERTIES OF A NEW TWO-PHOTON-ABSORBING MATERIAL TRANS-4-[p- (N-HYDROXYETHYL-N-ETHYLAMINO)STYRYL]- N-METHYLPYRIDINIUM p-TOLUENE SULFONATE

A new dye trans-4-[p-(N-hydroxyethyl-N-ethylamino)styryl]-N-methylpyridinium p-toluene sulfonate (HEASPS) has been synthesized. The two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a TPA cross-section of σ2 = 4.7 × 10-48 cm4 · s/photon at 1064 nm, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 625 nm up-converted lasing energy is 3.6% at the pump energy level of 4 mJ.

Synthesis and Properties of a New Two-photon-absorbed Material Heasps

A new dye Trans-4-[p-(N-hydroxyethyl-N-ethyiamino)styryl]-N-methylpyridinium p-toluene sulfonate (HEASPS) was synthesized, and the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a moderate TPA cross-section of\\sigma2 = 4.7 × 10−48 cm4 .s/photon at 1064nm, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 626 nm up-converted lasing energy is 18.2% at the pump energy level of 1.9 mJ.

Two-photon induced optical-power limiting and upconverted superradiance properties of a new organic dye HEASPI

A new organic dye trans-4-[ p-( N-ethyl- N-hydroxyethylamino)styryl]- N-methylpyridinium iodide (abbreviated as HEASPI hereafter) with large two-photon absorption (TPA) cross section and excellent upconverted superradiance properties was synthesized in our group recently. The TPA cross section was measured to be σ 2′=7.0×10 −48 cm 4 s/ photon by using an open aperture Z-scan system. Linear absorption, single-photon induced fluorescence, two-photon induced fluorescence and two-photon pumped (TPP) upconverted superradiance properties were systematically studied. The highest net upconversion efficiency from the absorbed pump energy to the output upconverted superradiance energy is as high as 19.6% at the pump energy of 2.07 mJ from a mode-locked Nd : YAG picosecond laser. The dye solution also shows a clear optical power limiting effect.

Studies on the lasing properties of a new two-photon absorbing material HEASPI

A new dye, trans-4-[ p-( N-ethyl- N-hydroxyethylamino)styryl]- N-methylpyridinium iodide has been synthesized, and the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped frequency up-converted lasing properties of this new dye were experimentally studied. This new dye has a TPA cross-section of σ 2=7.0×10 −48 cm 4 s/photon at 1064 nm, and exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 632 nm up-converted lasing energy is 4.3% at the pump power of 4 mJ.

Studies on two-photon pumped frequency up-converted lasing properties of a new material HMASPS

Abstract A new dye trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium p-toluene sulphonate (abbreviated as HMASPS) was synthesized, the two-photon absorption (TPA), TPA-induced frequency up-conversion emission, and two-photon pumped (TPP) frequency up-converted lasing properties of HMASPS were experimentally studied. This new dye has a moderate TPA cross-section of σ2 = 6.0 × 10−48 cm4 s photon−1, but exhibits a high lasing efficiency. The net conversion efficiency from the absorbed 1064 nm pump pulse energy to the 630 nm up-converted lasing energy is 4% at a pump energy level of 4mJ.