Simultaneous multiple wavelength upconversion in a core-shell nanoparticle for enhanced near infrared light harvesting in a dye-sensitized solar cell

Near-infrared laser-irradiated upconversion nanoparticles with dexamethasone precise released for alleviating lung ischemia-reperfusion injury

Introduction: Dexamethasone (DEX), as an important enduring-effect glucocorticoid (GC), holds great promise in the field of lung ischemia-reperfusion injury (LIRI) comprehensive therapy owing to its immunomodulatory properties, such as inducing apoptosis and cell cycle distribution. However, its potent anti-inflammatory application is still restricted because of multiple internal physiologic barriers. Methods: Herein, we developed upconversion nanoparticles (UCNPs) coated with photosensitizer/capping agent/fluorescent probe-modified mesoporous silica (UCNPs@mSiO₂[DEX]-Py/β-CD/FITC, USDPFs) for precise DEX release synergistic LIRI comprehensive therapy. The UCNPs were designed by covering an inert YOF:Yb shell on the YOF:Yb, Tm core to achieve high-intensity blue and red upconversion emission upon Near-Infrared (NIR) laser irradiation. Results: Under suitable compatibility conditions, the molecular structure of photosensitizer can be damaged along with capping agent shedding, which endowed USDPFs with an outstanding capability to carry out DEX release controlling and fluorescent indicator targeting. Furthermore, the hybrid encapsulating of DEX significantly increased utilization of nano-drugs, improving the water solubility and bioavailability, which was conducive to developing the anti-inflammatory performance of USDPFs in the complex clinical environment. Discussion: The response-controlled release of DEX in the intrapulmonary microenvironment can reduce normal cell damage, which can effectively avoid the side effects of nano-drugs in anti-inflammatory application. Meanwhile, the multi-wavelength of UCNPs endowed nano-drugs with the fluorescence emission imaging capacity in an intrapulmonary microenvironment, providing precise guidance for LIRI.

Upconversion lanthanide nanomaterials: basics introduction, synthesis approaches, mechanism and application in photodetector and photovoltaic devices

Upconversion (UC) of lanthanide-doped nanostructure has the unique ability to convert low energy infrared (IR) light to high energy photons, which has significant potential for energy conversion applications. This review concisely discusses the basic concepts and fundamental theories of lanthanide nanostructures, synthesis techniques, and enhancement methods of upconversion for photovoltaic and for near-infrared (NIR) photodetector (PD) application. In addition, a few examples of lanthanide-doped nanostructures with improved performance were discussed, with particular emphasis on upconversion emission enhancement using coupling plasmon. The use of UC materials has been shown to significantly improve the NIR light-harvesting properties of photovoltaic devices and photocatalytic materials. However, the inefficiency of UC emission also prompted the need for additional modification of the optical properties of UC material. This improvement entailed the proper selection of the host matrix and optimization of the sensitizer and activator concentrations, followed by subjecting the UC material to surface-passivation, plasmonic enhancement, or doping. As expected, improving the optical properties of UC materials can lead to enhanced efficiency of PDs and photovoltaic devices.

Photon Upconversion for Photovoltaics and Photocatalysis: A Critical Review

Opportunities for enhancing solar energy harvesting using photon upconversion are reviewed. The increasing prominence of bifacial solar cells is an enabling factor for the implementation of upconversion, however, when the realistic constraints of current best-performing silicon devices are considered, many challenges remain before silicon photovoltaics operating under nonconcentrated sunlight can be enhanced via lanthanide-based upconversion. A photophysical model reveals that >1-2 orders of magnitude increase in the intermediate state lifetime, energy transfer rate, or generation rate would be needed before such solar upconversion could start to become efficient. Methods to increase the generation rate such as the use of cosensitizers to expand the absorption range and the use of plasmonics or photonic structures are reviewed. The opportunities and challenges for these approaches (or combinations thereof) to achieve efficient solar upconversion are discussed. The opportunity for enhancing the performance of technologies such as luminescent solar concentrators by combining upconversion together with micro-optics is also reviewed. Triplet-triplet annihilation-based upconversion is progressing steadily toward being relevant to lower-bandgap solar cells. Looking toward photocatalysis, photophysical modeling indicates that current blue-to-ultraviolet lanthanide upconversion systems are very inefficient. However, hope remains in this direction for organic upconversion enhancing the performance of visible-light-active photocatalysts.

Recent advances of lanthanide-doped upconversion nanoparticles for biological applications

Near infrared (NIR) excited lanthanide-doped upconversion nanoparticles (UCNPs) are emerging as a new type of fluorescent tag for biological applications, which can emit multi-photon ultraviolet, visible or NIR luminescence for imaging or activation of photosensitive molecules. Here, we present a comprehensive review on recent advances of UCNPs for a manifold of biological applications, including upconversion mechanisms, building bright multicolor upconversion nanocrystals, single nanoparticle and super resolution imaging, in vivo optical and multimodal imaging, photodynamic therapy, light-controlled drug release, biosensing, and toxicities. Our perspectives on the future development of UCNPs are also described.

Preparation of YbF3-Ho@TiO2 core–shell sub-microcrystal spheres and their application to the electrode of dye-sensitized solar cells

The TiO₂/YbF₃-Ho@TiO₂ heterostructure with light-scattering and NIR-light harvesting characteristics can facilitate charge separation, suppress recombination process and prolong the lifetime of electrons.

nanocrystals (0 ≤ x ≤ 1): growth, size control and shell formation on β-NaCeF4:Tb core particles

is an interesting shell material for β-NaREF₄ particles of the lighter lanthanides (RE = Ce, Pr, Nd), as variation of its strontium content x allows to vary its lattice parameters and match those of the core material.

Microlens array enhanced upconversion luminescence at low excitation irradiance

The dearth of high upconversion luminescence (UCL) intensity at low excitation irradiance hinders the prevalent application of lanthanide-doped upconversion nanoparticles (UCNPs) in many fields ranging from optical bioimaging to photovoltaics. In this work, we propose to use microlens arrays (MLAs) as spatial light modulators to manipulate the distribution of excitation light fields in order to increase UCL, taking advantage of its nonlinear response to the excitation irradiance. We show that multicolored UCL from NaYF₄:Yb³⁺,Er³⁺@NaYF₄:Yb³⁺,Nd³⁺ and NaYF₄:Yb³⁺,Tm³⁺@NaYF₄:Yb³⁺,Nd³⁺ core/shell UCNPs can be increased by more than one order of magnitude under either 980 or 808 nm excitation, by simply placing a polymeric MLA onto the top of these samples. The observed typical green (525/540 nm) and red (654 nm) UCL bands from Er³⁺ and a blue (450/475 nm) UCL band from Tm³⁺ exhibit distinct enhancement factors due to their different multi-photon processes. Importantly, our ray tracing simulation reveals that the MLA is able to spatially confine the excitation light (980 and 808 nm) by orders of magnitude, thus amplifying UCL by more than 225-fold (the 450 nm UCL band of Tm³⁺) at low excitation irradiance. The proposed MLA method has immediate ramifications for the improved performance of all types of UCNP-based devices, such as UCNP-enhanced dye sensitized solar cells demonstrated here.

Near infrared harvesting dye-sensitized solar cells enabled by rare-earth upconversion materials

Dye-sensitized solar cells (DSSCs) have been deemed as promising alternatives to silicon solar cells for the conversion of clean sunlight energy into electricity.

A protected excitation-energy reservoir for efficient upconversion luminescence

Lanthanide-doped upconversion nanoparticles (UCNPs) are of great interest for biomedical applications. Currently, the applicability of UCNP bionanotechnology is hampered by the generally low luminescence intensity of UCNPs and inefficient energy transfer from UCNPs to surface-bound chromophores used e.g. for photodynamic therapy or analyte sensing. In this work, we address the low-efficiency issue by developing versatile core-shell nanostructures, where high-concentration sensitizers and activators are confined in the core and shell region of representative hexagonal NaYF₄:Yb,Er UCNPs. After doping concentration optimization, the sensitizer-rich core is able to harvest/accumulate more excitation energy and generate almost one order of magnitude higher luminescence intensity than conventional homogeneously doped nanostructures. At the same time, the activator ions located in the shell enable a ∼6 times more efficient resonant energy transfer from UCNPs to surface-bound acceptor dye molecules due to the short distance between donor-acceptor pairs. Our work provides new insights into the rational design of UCNPs and will greatly increase the general applicability of upconversion nanotechnologies.

Enhancing dye-sensitized solar cell efficiency through broadband near-infrared upconverting nanoparticles

The inability to utilize near infrared (NIR) light has posed a stringent limitation for the efficiencies of most single-junction photovoltaic cells such as dye-sensitized solar cells (DSSCs). Here, we describe a strategy to alleviate the NIR light harvesting problem by upconverting non-responsive NIR light in a broad spectral range (over 190 nm, 670-860 nm) to narrow solar-cell-responsive visible emissions through incorporated dye-sensitized upconversion nanoparticles (DSUCNPs). Unlike typically reported UCNPs with narrow and low NIR absorption, the organic dyes (IR783) anchored on the DSUCNP surface were able to harvest NIR photons broadly and efficiently, and then transfer the harvested energy to the inorganic UCNPs (typically reported), entailing an efficient visible upconversion. We show that the incorporation of DSUCNPs into the TiO₂ photoanode of a DSSC is able to elevate its efficiency from 7.573% to 8.568%, enhancing the power conversion efficiency by about 13.1%. We quantified that among the relative efficiency increase, 7.1% arose from the contribution of broad-band upconversion in DSUCNPs (about ∼3.4 times higher than the highest previously reported value of ∼2.1%), and 6.0% mainly from the scattering effect of DSUCNPs. Our strategy has immediate implications for the use of DSUCNPs to improve the performance of other types of photovoltaic devices.

Emerging ≈800 nm Excited Lanthanide-Doped Upconversion Nanoparticles

Lanthanide-doped upconversion nanoparticles can tune near-infrared light to visible or even ultra-violet light in emissions. Due to their unique photophysical and photochemical properties, as well as their promising bioapplications, there has been a great deal of enthusiastic research performed to study the properties of lanthanide-doped upconversion nanoparticles in the past few years. Despite the considerable progress in this area, numerous challenges associated with the nanoparticles, such as a low upconversion efficiency, limited host materials, and a confined excitation wavelength, still remain, thus hindering further development with respect to their applications and in fundamental science. Recently, innovative strategies that utilize alternative sensitizers have been designed in order to engineer the excitation wavelengths of upconversion nanoparticles. Here, focusing on the excitation wavelength at ≈800 nm, recent advances in the design, property tuning, and applications of ≈800 nm excited upconversion nanoparticles are summarized. Benefiting from the unique features of ≈800 nm light, including deep tissue penetration depth and low photothermal effect, the ≈800 nm excited upconversion nanoparticles exhibit superior potential for biosensing, bioimaging, drug delivery, therapy, and three dimensional displays. The critical aspects of such emerging nanoparticles with regards to meeting the ever-changing needs of future development are also discussed.

Phase angle encoded upconversion luminescent nanocrystals for multiplexing applications

Lanthanide-doped upconversion nanoparticles (UCNPs) are increasingly used as luminescent candidates in multiplexing applications due to their excellent optical properties. In the past, several encoding identities have been proposed for UCNPs, including emission colour, intensity ratio between different emission bands, colour spatial distribution, and luminescence lifetime. In this paper, a new optical encoding dimension for upconversion nanomaterials is developed by exploring their luminescence kinetics, i.e., the phase angle of upconversion luminescence in response to a harmonic-wave excitation. Our theoretical derivation shows that the phase angle is governed jointly by the rise and decay times, characterizing the upconversion luminescence kinetics. Experimentally, a full set of methods are developed to manage the upconversion luminescence kinetics, through which the rise and decay times can be manipulated dependently or independently. Furthermore, a large phase-angle space is achieved in which tens of unique codes can potentially be generated in the same colour channel. Our work greatly extends the multiplexing capacity of UCNPs, and offers new opportunities for their applications in a wide range such as microarray assays, bioimaging, anti-counterfeiting, deep tissue multiplexing labelling/detection and high-density data storage. In addition, the development of this luminescence kinetics-based optical encoding strategy is also instructive for developing multiplexing techniques using other cascade luminescent systems that inherently lack multi-spectral channels, such as triplet-triplet annihilation molecule pairs.

Insight into the interactions between nanoparticles and cells

This review summarizes the latest advances in nanoparticle (NP)–cell interactions. The influence of NP size, shape, shell structure, surface chemistry and protein corona formation on cellular uptake and cytotoxicity is highlighted in detail. Their impact on other cellular responses such as cell proliferation, differentiation and cellular mechanics is also discussed.

Huge enhancement of upconversion luminescence by dye/Nd3+ sensitization of quenching-shield sandwich structured upconversion nanocrystals under 808 nm excitation

A highly efficient UCL under excitation at 808 nm was achieved by dye/Nd³⁺ sensitization of quenching-shield sandwich structured upconversion nanocrystals.

Dye-sensitized lanthanide-doped upconversion nanoparticles

Dye sensitized lanthanide upconversion entails optical upconversion with unprecedented luminescence brightness and broadband excitation wavelength.

Plasmon-Induced Broadband Light-Harvesting for Dye-Sensitized Solar Cells Using a Mixture of Gold Nanocrystals

The efficiency of dye-sensitized solar cells (DSSCs) is generally limited by the mismatch between the absorption spectrum of the photosensitizer and the solar irradiation spectrum. This work describes the use of a mixture that containing proper proportions of SiO2 coated Au nanospheres (AuNSs@SiO2 ) and Au nanorods (AuNRs@SiO2 ) (the mixture was denoted as AuNCs@SiO2 ) to enhance the sunlight utility in DSSCs. The incorporation of AuNCs@SiO2 into the TiO2 photoanode induced broadband light-harvesting at both low- and long- wavelengths and thus enhanced the photocurrent compared to that of plasmonic solar cells based on either AuNSs@SiO2 or AuNRs@SiO2 . Upon the doping of AuNCs@SiO2 , the overall power conversion efficiency (PCE) increased from 7.39 to 9.12 % for DSSCs based on organic liquid electrolytes.

Enhanced photovoltaic performance of dye-sensitized solar cells using a new photoelectrode material: upconversion YbF3-Ho/TiO2 nanoheterostructures

New up-conversion YbF3-Ho/TiO2 (UC/TiO2) nanoheterostructures are designed and explored as an efficient photoelectrode material to yield dye-sensitized solar cells (DSSCs) with enhanced performance. In this study, we analyze the photogenerated charge transfer properties of the UC/TiO2 nanoheterostructures via surface photovoltage (SPV) and transient photovoltage (TPV) techniques, and the interfacial dynamics of charge transfer and recombination processes in DSSCs using electrochemical impedance spectroscopy (EIS) and open circuit photovoltage decay (OCVD) techniques. It is found that these UC/TiO2 nanoheterostructures combine the upconversion function of YbF3-Ho and the semiconductive merits from TiO2. More importantly, the hetero-junction interface in the UC/TiO2 nanoheterostructures not only induces direct electron-injection from YbF3-Ho to TiO2 by utilizing near-infrared light, but also further improves the existing merits of TiO2 through facilitating the interfacial photoinduced charge separation, suppressing the photoinduced charge recombination and prolonging the lifetimes of excited electrons, which can give further improvement of the photovoltaic performances. When integrating the UC/TiO2 nanoheterostructures into DSSCs, an overall energy conversion efficiency of 8.0% is achieved. There is a 23% enhancement in the overall conversion efficiency and a 19% improvement in the photocurrent, compared to the pristine devices.

A broad spectrum photon responsive, paramagnetic β-NaGdF4:Yb3+,Er3+ – mesoporous anatase titania nanocomposite

Herein, we report a novel single multifunctional platform based on broad-spectrum photoactive β-NaGdF₄:18% Yb³⁺, 2% Er³⁺ and mesoporous anatase TiO₂ for enhanced energy and simultaneous biomedical applications.

Giant enhancement of upconversion emission in NaYF4:Er3+@NaYF4:Yb3+ active-core/active-shell nanoparticles

An effective method to enhance greatly infrared-visible upconversion emissions of Er³⁺ ions is demonstrated through coating an optimized active NaYF₄:Yb³⁺ shell around the NaYF₄:Er³⁺ core nanoparticles.

Enhanced Photovoltaic Performance of Dye-Sensitized Solar Cells by Efficient Near-Infrared Sunlight Harvesting using Upconverting Y2O 3:Er (3+)/Yb (3+) Phosphor Nanoparticles

We report the efficiency enhancement in dye-sensitized solar cells (DSSCs) using Er(3+)/Yb(3+)-co-doped Y2O3 (i.e., Y2O3:Er(3+)/Yb(3+)) phosphor nanoparticles, prepared by a simple and cost-effective urea-based homogeneous precipitation method, for efficient near-infrared (NIR) sunlight harvesting. Under the light excitation at a wavelength of 980 nm, the as-prepared samples exhibited strong upconversion emissions at green and red visible wavelengths. To investigate the influence of Y2O3:Er(3+)/Yb(3+) nanoparticles on the photovoltaic performance of DSSCs, the phosphor nanoparticles were incorporated into titanium dioxide films to form a composite photoelectrode. For the resulting DSSCs, the increased power conversion efficiency (PCE) of 6.68 % was obtained mainly by the increased photocurrent of J SC = 13.68 mA/cm(2) due to the light harvesting enhancement via the NIR-to-visible upconversion process (cf., PCE = 5.94 %, J SC = 12.74 mA/cm(2) for the reference DSSCs without phosphor nanoparticles), thus, indicating the PCE increment ratio of ~12.4 %.

Triple-doped KMnF3:Yb3+/Er3+/Tm3+ nanocubes: four-color upconversion emissions with strong red and near-infrared bands

Triple-doped (Yb³⁺/Er³⁺/Tm³⁺) KMnF₃ nanocubes with uniform sizes of 250 nm were synthesized by a facile hydrothermal route using the oleic acid as the capping agent. It was found that these nanocubes can simultaneously exhibited four-color (blue, green, red and NIR) upconversion emissions under a single 980 nm near-infrared (NIR) laser excitation, which should have potential multicolor in vivo imaging applications. Specifically, the red (660 nm) and NIR (800 nm) peaks, known as two “optical windows” for imaging biological tissues, were strong. The spectral and pump analyses indicated the two-photon processes were responsible for the both red and NIR emissions.

Enhancing Solar Cell Efficiency Using Photon Upconversion Materials

Photovoltaic cells are able to convert sunlight into electricity, providing enough of the most abundant and cleanest energy to cover our energy needs. However, the efficiency of current photovoltaics is significantly impeded by the transmission loss of sub-band-gap photons. Photon upconversion is a promising route to circumvent this problem by converting these transmitted sub-band-gap photons into above-band-gap light, where solar cells typically have high quantum efficiency. Here, we summarize recent progress on varying types of efficient upconversion materials as well as their outstanding uses in a series of solar cells, including silicon solar cells (crystalline and amorphous), gallium arsenide (GaAs) solar cells, dye-sensitized solar cells, and other types of solar cells. The challenge and prospect of upconversion materials for photovoltaic applications are also discussed.

Tuning upconversion through a sensitizer/activator-isolated NaYF₄ core/shell structure

The ability to tune the emission color of upconversion nanoparticles (UCNPs) will greatly enhance the scope of their applications, ranging from infrared solar cells to volumetric multiplexed bioimaging. Conventional methods to tune upconversion are to vary the type and/or the concentration of doped rare-earth ions in these nanoparticle formulations. Here, we introduce a different approach to vary the emission colors of the frequently used sensitizer/activator pairs of Yb(3+)/RE(3+) (RE = Ho, Er, Tm) via utilization of a sensitizer/activator-isolated NaYF4 core-shell structure. We show that the typical green, yellow, and blue luminescent colors from Yb(3+)/Ho(3+)-, Yb(3+)/Er(3+)-, and Yb(3+)/Tm(3+)-co-doped NaYF4 UCNPs can be converted into the quasi-white, green, and pink blue, when corresponding core-shell structures of NaYF4:Yb(3+) @NaYF4:Ho(3+), NaYF4:Yb(3+) @NaYF4:Er(3+) and NaYF4:Yb(3+) @NaYF4:Tm(3+) are built. Time-resolved spectra indicate that decay lifetimes of the emission bands from the sensitizer/activator-isolated core-shell structure significantly vary from that of the sensitizer/activator-codoped NaYF4 UCNPs, verifying the strain-induced modulation of emission channels in the core-shell structure. These sensitizer-activator-isolated core-shell UCNPs have implications for a range of biophotonic or photonic applications.

An anion-induced hydrothermal oriented-explosive strategy for the synthesis of porous upconversion nanocrystals

Rare-earth (RE)-doped upconversion nanocrystals (UCNCs) are deemed as the promising candidates of luminescent nanoprobe for biological imaging and labeling. A number of methods have been used for the fabrication of UCNCs, but their assembly into porous architectures with desired size, shape and crystallographic phase remains a long-term challenging task. Here we report a facile, anion-induced hydrothermal oriented-explosive method to simultaneously control size, shape and phase of porous UCNCs. Our results confirmed the anion-induced hydrothermal oriented-explosion porous structure, size and phase transition for the cubic/hexagonal phase of NaLuF4 and NaGdF4 nanocrystals with various sizes and shapes. This general method is very important not only for successfully preparing lanthanide doped porous UCNCs, but also for clarifying the formation process of porous UCNCs in the hydrothermal system. The synthesized UCNCs were used for in vitro and in vivo CT imaging, and could be acted as the potential CT contrast agents.