High-performance Upconversion Research Articles

Near-Infrared-to-Visible Photon Upconversion with Efficiency Exceeding 21% Sensitized by InAs Quantum Dots.

Upconversion (UC) of incoherent near-infrared (NIR) photons to visible photons through sensitized triplet-triplet annihilation (TTA) shows great potential in solar energy harvesting, photocatalysis, and bioimaging. However, the efficiencies of NIR-to-visible TTA-UC systems lag considerably behind those of their visible-to-visible counterparts. Here, we report a novel NIR-to-yellow TTA-UC system with a record quantum yield (QY) of 21.1% (out of a 100% maximum) and a threshold intensity of 20.2 W/cm2 by using InAs-based colloidal quantum dots (QDs) as triplet photosensitizers. The key to success is the epitaxial growth of an ultrathin ZnSe shell on InAs QDs that passivates the surface defects without impeding triplet energy transfer (TET) from QDs to surface-bound tetracene. Transient absorption spectroscopy verifies efficient TET efficiency of more than 80%, along with sufficiently long triplet lifetime of tetracene molecules, leading to high-performance UC. Moreover, high UC QYs (>18%) remain when larger InAs-based QDs─of which the absorption peak is red-shifted by more than 50 nm─are used as sensitizers, indicating the great potential of InAs QDs to utilize NIR photons with lower energy.

Interfacial Engineering of High-Performance Upconversion Hydrogels with Orthogonal NIR Photochemistry in Vivo for Synergistic Noninvasive Biofilm Elimination and Tissue Repair

Interfacial Engineering of High-Performance Upconversion Hydrogels with Orthogonal NIR Photochemistry in Vivo for Synergistic Noninvasive Biofilm Elimination and Tissue Repair

Point-of-care detection of Monkeypox virus clades using high-performance upconversion nanoparticle-based lateral flow assay.

There is an urgent need for a point-of-care testing (POCT) method in developing and underserved regions to distinguish between two Monkeypox virus (MPXV) clades, given their varying transmissibility and clinical manifestations. In this paper, we target the specific complement protein gene fragment of two MPXV clades and construct a high-performance upconversion nanoparticles-based lateral flow assay (UCNPs-based LFA) with double T-lines and a shared C-line. This enables qualitativeandquantitative dual-mode detection when combined with a smartphone and a benchtop fluorescence analyzer. The developed LFA exhibits stable performance, convenient operation, rapid readout (within 8min), and a much lower limit of detection (LOD) (~ pM level) compared to existing POCT methods. The proposed detection platform demonstrates significant potential for pathogen diagnosis using a POCT approach.

Anomalous power-dependent color tuning of Er upconverting luminescence via 1530 nm excitation

The upconversion color tuning of Lanthanide ions usually requires complex core–shell structures and excitation configurations. This work presents simple Er3+ doped Yttria phosphors capable of color change through the manipulation of 1530 nm excitation intensity. Compared to the reported results of Er3+ color change from green to red with the increase in excitation intensity, the formed color-tunable phosphors show an inverse change of red to green. The color tuning mechanisms are attributed to the competition between the upward absorption and the downward decay at the Er3+ intermediate state. Finally, the potential applications of the formed color-tunable phosphors are demonstrated. This work provides a simple solution for high-performance upconversion color tuning and thus shows wide application prospects.

Upconversion luminescence enhancement and color modulation in Yb3+/Er3+/Ln3+ (Ln = Tm, Ho) tri-doped YF3 microrods

Intelligent regulation of energy transfer process among different rare earth ions doped in the matrix is an effective strategy to realize high-performance upconversion (UC) luminescence. Based on this, wheat ears like Yb3+/Er3+/(Tm3+, Ho3+) triple doped YF3 microrods were fabricated via hydrothermal method, and the morphology, crystal structure, UC luminescence performance dependent on Tm3+/Ho3+ doping concentrations were studied. By comparing with the Yb3+, Er3+ co-doped YF3 microrods, the UC luminescence intensity is enhanced in Yb3+/Er3+/(Tm3+, Ho3+) triple doped YF3 samples due to the cross relaxation processes between Er3+ and Tm3+/Ho3+. Moreover, red emission is enhanced more significantly than green emission in YF3: Yb3+, Er3+, Tm3+, which is contrary to that in YF3: Yb3+, Er3+, Ho3+. The possible energy transfer upconversion mechanism involved is discussed in detail. Meanwhile, an adjustable emission color is easy to achieve via altering the doped Er3+/Tm3+/Ho3+ ion concentration. These studies on the UC luminescence enhancement mechanism of Yb3+/Er3+/(Tm3+, Ho3+) triple doped YF3 microrods are expected to provide a reference for the development of high-efficiency luminescent materials.

Highly luminescent Gd2O2S:Er3+,Yb3+ upconversion microcrystals obtained by a time- and energy-saving microwave-assisted solid-state synthesis

Er3+-doped and Er3+,Yb3+-co-doped Gd2O2S are one of the most efficient upconversion (UC) materials available to date. However, preparing lanthanide oxysulfides can be challenging as it requires several hours of heating at>1000 °C in high power furnaces. Nonetheless, in designing a new synthesis technology for UC materials, one should consider that these systems suffer from defect quenching, responsible for significant optical energy losses. In this work, the microwave-assisted solid-state (MASS) synthesis was explored as an alternative to synthesize this class of materials, using two different starting compounds – lanthanide oxides (Ln2O3) and hydroxycarbonates (Ln(OH)CO3), where Ln3+: Gd, Er, Yb. Different Er3+,Yb3+ concentrations were investigated, and the Er3+(5%),Yb3+(5%) and Er3+(1%),Yb3+(10%) were shown to give the most intense UC output comparable to commercially available materials. Using Ln(OH)CO3 instead of the more common Ln2O3 for the MASS synthesis contributed to higher UC efficiencies and a more homogeneous Er3+ and especially Yb3+ distribution through the Gd2O2S lattice as verified by luminescence lifetime measurements. These high-quality materials were prepared in a simple two-step synthesis of 50 min and using a domestic microwave oven, leading to a remarkable decrease of 79% in processing time and 93% in energy consumption, making the MASS method suitable to be explored as an alternative synthesis methodology for high performance UC materials.

Solution-processed upconversion photodetectors based on quantum dots

Upconversion photodetectors convert photons from the infrared to the visible light spectrum and are of use in applications such as infrared detection and imaging. High-performance upconversion devices are, however, typically based on vacuum-deposited materials, which are expensive and require high operating voltages, which limits their implementation in flexible systems. Here we report solution-processed optical upconversion photodetectors with a high photon-to-photon conversion efficiency of 6.5% and a low turn-on voltage of 2.5 V. Our devices consist of a colloidal lead sulfide quantum dot layer for harvesting infrared light that is monolithically coupled to a cadmium selenide/zinc selenide quantum dot layer for visible-light emission. We optimized the charge-extraction layers in these devices by incorporating silver nanoparticles into the electron transport layers to enable carrier tunnelling. Our photodetectors exhibit a low dark current, high detectivity (6.4 × 1012 Jones) and millisecond response time, and are compatible with flexible substrates. We also show that the devices can be used for in vitro bioimaging. By embedding silver nanoparticles in the electron transport layer, solution-processed quantum-dot-based photodetectors with a high photon-to-electron conversion efficiency of 6.5% and a low turn-on voltage of 2.5 V can be created for use in infrared imaging applications.

Effects of Ca2+ doping on upconversion luminescence intensity and crystal field asymmetry of β-NaYF4:Yb3+/Er3+ microcrystals

The green and red upconversion (UC) emissions of 35 mol% Ca2+ doped β-NaYF4:Yb3+/Er3+ microcrystals were improved to 102.8 and 43.1 times higher than those of Ca2+-free counterparts. X-ray powder diffraction spectra, scanning electron microscopy, Fourier transform infrared spectroscopy, upconversion luminescence (UCL) spectroscopy and Judd-Ofelt analysis were performed to investigate the mechanism of UCL intensity enhancement caused by Ca2+ doping. The hexagonal-to-cubic phase transition was observed when Ca2+ doping concentration exceeded 35 mol%. The incorporation of Ca2+ into hexagonal microcrystals lattice induced unit cell volume enhancement and microcrystals surface to volume ratio variation, which affected the UCL intensity by hindering the non-radiative energy loss process via Yb3+/Er3+ ions and changing the amount of surface quenchers adsorbed on the microcrystals surface. The hypersensitive transition related local crystal field asymmetry around Er3+ in the grown hexagonal microcrystals was also investigated by Judd-Ofelt analysis but unexpectedly found to be the less dominant factor for the UCL intensity variation. This study helps to realize the mechanism of impurity ion doping resulted UCL intensity enhancement, which is instructive for high-performance UC microcrystals synthesis.

The construction of sublattice level energy cluster for promoting UV upconversion emission in tetragonal LiYF4

The preparation of high performance upconversion luminescence materials with stronger shortwave emissions is still a challenge. In this work, the feature of hexagon circles sublattice structure of tetragonal LiYF4 was revealed, and the sublattice level energy clusters of 4 Yb3+-1Tm3+ were constructed by the substitution of 70 mol% Yb3+ for Y3+ in tetragonal LiYF4 matrix. The sensitizing ions concentration quenching was inhibited by the hexagon circles sublattice structure, and the upconversion luminescence was dramatically enhanced, especially, the UV band emission was enhanced about 20 times and the intensity ratio of UV to blue emissions was improved about 10 folds under the excitation power density of 0.230 W/cm2. Photon numbers of upconversion emissions obviously decreased with the increasing of sublattice level energy clusters that the upconversion process of three photons was changed to two steps of two photons process. The upconversion luminescence mechanism of sublattice energy cluster construction was system investigated. The material with high performance of UV and blue UC luminescence can be a well candidate for the applications of photodynamic therapy and photocatalytic, etc. The work may be an inspiration for high efficient UC luminescence materials design and preparation.

Significantly enhanced luminescence of dual wavelength excitation upconversion nanoparticles by two-dimensional technique

In this work, the monodisperse NaGdF4@ NaGdF4:Yb/Er @ NaGdF4:Yb/Nd nanoparticles have been prepared via a modified solvothermal method. Under the 808 nm or 980 nm excitation, a bright upconversion luminescence （UCL）of the inert-core/luminescent-shell/active-shell nanoparticles can be both observed. Importantly, the intensity of luminescence is up to around 25-fold that of NaGdF4:Yb/Er @ NaGdF4:Yb/Nd core-shell nanoparticles under 808 nm excitation, which is more advantageous in biological application. This is because, compared with the traditional core-shell structure, the two-dimensional doping (inert-core/luminescent-shell/active-shell) design not only reduces the distance between Yb3+ and Er3+ ions, but also further reduces the energy loss by physically separating Er3+ from the nuclei with a large number of defects, which are both conducive to the improvement of energy transfer efficiency. This research will provide important reference value for the development of high-performance up-conversion nanomaterials.

Room-temperature up-conversion random lasing from CsPbBr3 quantum dots with TiO2 nanotubes

We report successful room-temperature up-conversion random lasing by distributing CsPbBr3 quantum dots (QDs) uniformly into TiO2 nanotubes (NTs). In order to overcome the difficulty in purifying the QDs, TiO2 NTs were designed to collect QDs and enhance the optical multiple scattering effect. A threshold of 9.54 mJ/cm2 and narrow full width at half-maximum of 0.49nm with a relatively high quality factor of 1089 were successfully observed. These results indicate that CsPbBr3QDs/TiO2 NTs can be high-performance up-conversion lasers for practical applications, especially when the phase matching required by conventional approaches cannot be fulfilled.

Tin-(IV) dopant-controlled synthesis of Yb3+/Er3+:NaGdF4 nanocrystals: Morphology transformation and intensified upconversion performance

Hexagonal Yb3+/Er3+:NaGdF4 nanocrystals codoped with Sn4+ ions were produced via an adjustive solvothermal approach. Simultaneous morphology regulation and intensified upconversion (UC) luminescence of Yb3+/Er3+:NaGdF4 nanocrystals were achieved through Sn4+ ions doping. Upon introducing Sn4+ ions into the NaGdF4 host, a part of the nanocrystals were converted to nanocubes. By optimizing the Sn4+ ions doping content to 40 mol%, UC luminescence intensity of the green and red emissions were intensified by 21 and 31 times, respectively. Moreover, the possible mechanisms for morphology transformation and UC luminescence enhancement of Sn4+-doped Yb3+/Er3+:NaGdF4 nanocrystals were discussed elaborately. Additionally, in contrast to the sample fabricated by co-precipitation method, the result indicated that the UC luminescence intensity with 40 mol% Sn4+ ions doping was about 2.5 times higher than the former one. This research could be helpful for designing high-performance UC materials and fulfilling their practical applications.

Stannum-(II) dopant effects on morphology evolution and upconversion performance of Yb3+/Er3+:NaGdF4 crystals

Abstract Hexagonal Yb 3+ /Er 3+ :NaGdF 4 nanocrystals codoped with Sn 2+ ions were prepared via a modulated solvothermal method. Upon introducing 25mol% Sn 2+ ions into the host lattice by substituting Gd 3+ ions, a portion of Yb 3+ /Er 3+ :NaGdF 4 nanocrystals was converted into nanorods. Meanwhile, the upconversion (UC) luminescence intensity of 542 nm and 652 nm were intensified by 24 and 33 times respectively, when compared with samples without Sn 2+ ions doping. The effect of Sn 2+ ions doping content on the morphology and UC emission performances of Yb 3+ /Er 3+ :NaGdF 4 nanocrystals were discussed in detail. The enhancement of UC luminescence intensity could be attributed to the growth of UC nanocrystals and the low crystal local symmetry around Yb 3+ /Er 3+ ion pairs. This study may be beneficial for fabricating high-performance UC materials and realizing their practical applications.

Highly sensitive liquid crystal optically addressed spatial light modulator for infrared-to-visible image up-conversion.

A liquid crystal optically addressed spatial light modulator based on an InGaAs photodiode array operating at low light levels is investigated in the short wavelength infrared (SWIR) spectral band to serve as a SWIR-to-visible imaging upconversion device. It consists of InGaAs/InP heterojunction photodetectors array sandwiched with a nematic LC layer. The photodiode array is composed of a 640×512 InGaAs/Inp heterojunctions, grown on InP substrate with a 15μm pitch. Full up-converted visible images in stills and video modes were demonstrated with SWIR light intensities as low as 70 nW/cm2 or less than pW/pixel. The influence of operation frequency on the performance of the device was found theoretically and experimentally to be crucial for a proper operation of the device. The optimum sensitivity and contrast of the device was found at a frequency around 70Hz. To the best of our knowledge, this is the first time that such a high performance upconversion device is presented and that actual visible images are obtained.

High-performance upconversion luminescent waveguide using a rare-earth doped microtube with beveled ends

Upconversion luminescence-based waveguides can achieve optical signal transmission and visible light emission with near-infrared light excitation and their quality is highly dependent on the coupling efficiency between the light and waveguide.

Upconversion effective enhancement of NaYF4:Yb3+/Er3+ nanoparticles by Ni2+ doping

In this manuscript, Ni2+ ions-doped NaYF4:Yb3+/Er3+ nanoparticles have been synthesized via a modified hydrothermal method. The upconversion luminescence intensities of the green (G) and red (R) emission of NaYF4:Yb3+/Er3+ co-doped with 20 mol% Ni2+ ions are the strongest which increase 32.84 and 20.99 times than that without doping Ni2+, respectively. In addition, the R/G ratio decreases with the concentration of Ni2+ increasing from 0 to 40 mol%. The underlying reason for luminescence enhanced and the R/G ratio decreased by Ni2+ doping is explored by a series of controlled experiments, and the mechanism based on the crystal field asymmetry, different substitution by Ni2+, the energy transition of Er3+ is studied in detail. The study indicates that the misshapen crystal field plays an important role in enhancement fluorescence emission, and several factors affect the R/G ratio including the crystal field, the substitution site and the energy transition. Our result may play a certain function for study and design of high-performance upconversion materials.

Enhanced upconversion luminescence of NaYF4:Yb, Er microprisms via La3+ doping

A series of β-NaYF4: Yb, Er micro-prisms codoped with La3+(0–30at%) were synthesized via hydrothermal process. Upon 980nm excitation at room temperature, 20mol% La3+ codoped sample shows a maximum upconversion emission intensity. Excitation power density dependencies of UC luminescence and the decay curves were investigated. The UCPL decay is evidently monoexponential for all samples and La3+ doping did not significantly change the decay time. In this particular case, we found the napierian logarithm of the UC emission intensity (lnI) had a good linear relationship with the cell lattice parameters. This correlation may be helpful for design and fabrication of high performance upconversion materials.

High-Performance Upconversion Nanoprobes for Multimodal MR Imaging of Acute Ischemic Stroke.

Multimodal magnetic resonance (MR) imaging, including MR angiography (MRA) and MR perfusion (MRP), plays a critical role in the diagnosis and surveillance of acute ischemic stroke. However, these techniques are hindered by the low T1 relaxivity, short circulation time, and high leakage rate from vessels of clinical Magnevist. To address these problems, nontoxic polyethylene glycol (PEG)ylated upconversion nanoprobes (PEG-UCNPs) are synthesized and first adopted for excellent MRA and MRP imaging, featuring high diagnostic sensitivity toward acute ischemic stroke in high-resolution imaging. The investigations show that the agent possesses superior advantages over clinical Magnevist, such as much higher relaxivity, longer circulation time, and lower leakage rate, which guarantee much better imaging efficiency. Remarkably, an extremely small dosage (5 mg Gd kg(-1) ) of PEG-UCNPs provides high-resolution MRA imaging with the vascular system delineated much clearer than the Magnevist with clinical dosage as high as 108 mg Gd kg(-1) . On the other hand, the long circulation time of PEG-UCNPs enables the surveillance of the progression of ischemic stroke using MRA or MRP. Once translated, these PEG-UCNPs are expected to be a promising candidate for substituting the clinical Magnevist in MRA and MRP, which will significantly lengthen the imaging time window and improve the overall diagnostic efficiency.

Upconversion effective enhancement by producing various coordination surroundings of rare-Earth ions.

In this manuscript, we present a simple route to enhance upconversion (UC) emission by producing two different coordination sites of trivalent cations in a matrix material and adjusting crystal field asymmetry by Hf(4+) co-doping. A cubic phase, Y3.2Al0.32Yb0.4Er0.08F12, with these structural characteristics was synthesized successfully by introducing a small ion (Al(3+)) into YF3. X-ray diffraction (XRD), nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), X-ray spectroscopy (XPS), and fluorescence spectrophotometry (FS) were employed for its crystalline structure and luminescent property analysis. As a result, the coordination environments of the rare-earth ions were varied more obviously than a hexagonal NaYF4 matrix with the same Hf(4+) co-doping concentration, with vertical comparison, UC luminescent intensities of cubic Y3.2Al0.32Yb0.4Er0.08F12 were largely enhanced (∼32-80 times greater than that of different band emissions), while the maximum enhancement of hexagonal NaYF4 was by a factor of ∼12. According to our experimental results, the mechanism has been demonstrated involving the crystalline structure, crystal field asymmetry, luminescence lifetime, hypersensitive transition, and so on. The study may be helpful for the design and fabrication of high-performance UC materials.

Tuning crystal field symmetry of hexagonal NaY0.92Yb0.05Er0.03F4 by Ti4+ codoping for high-performance upconversion

378nm, 408nm and 521nm upconversion emissions of Er3+ ions were obviously enhanced by Ti4+ codoped with Yb3+/Er3+ in hexagonal NaYF4, and the corresponding upconversion luminescence lifetimes were also prolonged, especially for 378nm and 408nm emissions. X-ray powder diffraction, field emission scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and upconversion emission spectra were employed to explore the relationships of the structure and properties. From these characterizations we made a novel discovery that Na+ could be induced to occupy Y3+ sites for establishing valence balance of the system if Ti4+ ions were codoped with appropriate concentration. As a result the crystal field asymmetry of NaY0.92Yb0.05Er0.03F4 was enhanced and then its upconversion properties were improved because the hypersensitive electron transition of Yb3+/Er3+ ions was promoted greatly. At the same time, the crystal sizes of the codoped NaYF4 became smaller because the crystal growth was prevented by more negative charges gathering at the crystal surface. This study provides an exploration of the relationship among impurity doping, structural changes and upconversion performance, which may be useful for design and synthesis of high-performance upconversion codoping materials.