Upconversion Particles Research Articles

An aptasensor for ampicillin detection in milk by fluorescence resonance energy transfer between upconversion nanoparticles and Au nanoparticles.

This paper reports a portable fluorescence resonance energy transfer (FRET) aptasensor for ampicillin (Amp) detection using upconversion particles (UCNPs) as energy donors and Au nanoparticles (AuNPs) as energy acceptors. The optimal parameters of the detection system were investigated. Under the optimal conditions, it had a good linear relationship between the fluorescence intensities and Amp concentrations, a high coefficient of determination (R2) of 0.9939, a wide detection range of 10-100ng/mL, and a low limit of detection (LOD) of 3.9ng/mL; meanwhile, the aptasensor had high selectivity for Amp against the interference of other antibiotics, and had good recovery and repeatability. Also, its detection performance had been successfully validated by milk samples. Therefore, the developed aptasensor based on FRET between UCNPs and AuNPs has a good prospect for Amp on-site detection in milk with a portable upconversion detection instrument.

Temperature-responsive lanthanide-doped nanoarchitecture with orthogonal upconversion luminescence

Lanthanide-doped core-shell upconversion particles with tunable emission bands and intensities in response to external stimuli provide opportunities for multicolor barcoding, optical imaging, and temperature sensing applications. Here, we provide a universal template that can be used as a basic medium for color control and temperature sensing. In a representative nanostructure, i.e., NaYF4:Yb/[email protected]4:Yb/Tm, two excitation-emission spectra-orthogonal luminescence groups with naked-eye observable emission colors (cyan or yellow-green) were obtained by switching the excitation wavelength (980 and 1550 nm). Furthermore, the temperature-responsive optical performance of the nanostructure was investigated, and enhanced temperature sensitivities Sa (0.2339 K−1) and Sr (2.5286% K−1) were achieved based on 3F2,3/4S3/2 non-thermally coupled energy levels (NTCLs). The photophysical properties of the nanostructure show great potential for anticounterfeiting and non-contact temperature sensing applications.

Luminescent upconversion nanoparticles evaluating temperature-induced stress experienced by aquatic organisms owing to environmental variations

SummaryGrowing anthropogenic activities are significantly influencing the environment and especially aquatic ecosystems. Therefore, there is an increasing demand to develop techniques for monitoring and assessing freshwater habitat changes so that interventions can prevent irrevocable damage. We explore an approach for screening the temperature-induced stress experienced by aquatic organisms owing to environmental variations. Luminescent spectra of upconversion [Y2O3: Yb, Er] particles embedded within Caridina multidentata shrimps are measured, while ambient temperature gradient is inducing stress conditions. The inverse linear dependence of the logarithmic ratio of the luminescence intensity provides an effective means for temperature evaluation inside aquatic species in vivo. The measured luminescence shows high photostability on the background of the complete absence of biotissues’ autofluorescence, as well as no obscuration of the luminescence signal from upconversion particles. Current approach of hybrid sensing has a great potential for monitoring variations in aquatic ecosystems driven by climate changes and pollution.

The role of chelating agent on the structure and up-conversion property of NaLuF4:Yb,Tm as security ink phosphor

Purpose This study aims to investigate the effect of trisodium nitrilotriacetic acid (NTA) on the physical and luminescence emission properties of NaLuF4:Yb, Tm Upconversion (UC) particles and compared with trisodium citrate (CA). Upconversion materials have been remarkably considered in many applications in the past decades. However, the morphology of the UC particles affects their emission properties, depending on the synthesis situation. Design/methodology/approach The UC particles were synthesized by the hydrothermal method. Properties such as crystal phase, particle morphology, particle size, smoothness and uniformity of particle surface and their emission intensity in the UV–Vis region were studied. Findings Observations showed that pH is an essential factor in determining the crystalline phase. In addition, quality factors affect the morphology, particle size and surface smoothness of crystalline facets. It was also found that the UC particles synthesized in the presence of trisodium NTA have a much higher emission intensity than those synthesized in the presence of CA. The use of UC particles in security inks to maintain the brand was also investigated. Originality/value To the best of the authors’ knowledge, for the first time, the effect of trisodium NTA as a chelating agent was investigated on morphology and UC intensity of NaLuF4:Yb,Tm phosphor.

Microwave-assisted synthesis and upconversion luminescence of NaYF4:Yb, Gd, Er and NaYF4:Yb, Gd, Tm nanorods

Anisotropic rare earth ion (RE3+) doped fluoride upconversion particles are emerging as potential candidate in diverse areas, ranging from biomedical imaging to photonics. Here, we develop a facile strategy to synthesize NaYF4: Yb, Gd, Er, and NaYF4: Yb, Gd, Tm upconversion nanorods via microwave synthesis route by controlling the synthesis time and compared the optical properties similar nanorods prepared via solvothermal technique. With the increase in synthesis time, the phase of the particle found to change from mixed phase to purely hexagonal and morphology of the particles change mixed phase of spherical and rod-shaped particles to completely nanorods for a synthesis time of 60 min. Further, the intrinsically hydrophobic particles changed to hydrophilic by removal of oleic capping via acid treatment and the amine functionalized silica coating. The upconversion luminescence as well as laser power dependent emission properties of the surface modified particles elucidate that surface modification route influence the upconversion luminescence as well as solvent dependent emission properties. Moreover, the laser power dependent studies elucidate that the upconversion process in a multi-photon process.

Study of energy transfer processes between rare earth ions and photosensitizer molecules for photodynamic therapy with IR-excitation

Today, photodynamic therapy is one of the most promising minimally invasive methods of treatment of various diseases, including cancer. The main limitation of this method is the insufficient penetration into the tissue of laser radiation used to activate photosensitizer molecules, which makes it difficult to carry out therapy in the treatment of large or deep-seated tumors. In this regard, there is a great interest in the development of new strategies for photodynamic therapy using infrared radiation for excitation, the wavelengths of which fall into the “transparency window” of biological tissues. In this work, it was proposed to use upconversion NaGdF4 :Yb:Er nanoparticles (UCNP), which absorb infrared excitation and serve as a donor that transfers energy to the photosensitizer. Photosens and phthalosens were chosen as the most promising photosensitizers for the study. The aim of this work was to study the energy transfer processes between upconversion nanoparticles doped with rare-earth ions and photosensitizer molecules. in order to excite photosensitizers with IR radiation and carry out photodynamic therapy of deep-seated neoplasms. Using spectroscopic and time-resolved methods, it has been demonstrated that there is an efficient energy transfer between upconversion particles and photosensitizers phthalosens and photosens. The calculated efficiency of energy transfer by the Foerster mechanism was 41% for the UCNP + photosens system and 69% for the UCNP + phthalosens system. It has been experimentally and theoretically proved that there is a binding of photosensitizer molecules with UCNP by means of surfactants, leading to a reduction in the distance between them, due to which effective nonradiative energy transfer is realized. The generation of singlet oxygen by the phthalosens photosensitizer upon excitation by means of energy transfer from UCNP, excited at 980 nm wavelength of, has been demonstrated.

Upconversion Particles’ Role in Composite Materials: From Light Absorption to Energy Conversion

Upconversion Particles’ Role in Composite Materials: From Light Absorption to Energy Conversion

Laser Induced Thermal Effect on the Polymerization Behavior in Upconversion Particle Assisted Near-Infrared Photopolymerization.

Laser induced thermal effect is inevitable in upconversion particle assisted near-infrared polymerization (UCAP). Herein, the influence of thermal effects on the polymerization behavior are investigated. The effects of up-conversion particles content and NIR laser intensity on the polymerization rate and surface oxygen inhibition were systematically investigated, and the temperature evolution and complex viscosity changes in the polymerization system during the polymerization process were also monitored. In addition, polymerization experiments conducted on a controlled temperature platform were used to study the effect of NIR heating on the polymerization behavior. The results show that the near-infrared thermal effect promotes the polymerization reaction, but also causes severe oxygen inhibition which has an adverse effect on polymerization. Finally, NIR curing materials with enhanced mechanical properties than those of conventional UV curing materials were obtained.

Near-Infrared Light Induced Reverse Atom Transfer Radical Polymerization Assisted by Upconversion Particles

Near-Infrared Light Induced Reverse Atom Transfer Radical Polymerization Assisted by Upconversion Particles

Laser damage threshold of hydrophobic up-conversion carboxylated nanocellulose/SrF2:Ho composite films functionalized with 3-aminopropyltriethoxysilane

Luminescent nanocomposite films, containing SrF2:Ho up-conversion particles, were prepared by two different protocols from aqueous dispersions of TEMPO-oxidized cellulose nanofibrils (TOCNF) functionalized with 3-aminopropyltriethoxysilane (APS) without the use of organic solvents at pH = 4.0–4.5 and 9.0–9.5, respectively. Proposed synthetic protocols included the formation of the films by drying the dispersions containing pre-hydrolyzed APS adsorbed onto TOCNF and SrF2:Ho particles followed by heating at 105 °C. Hydrophobic (water contact angle 101 ± 2°), strong, and translucent TOCNF/SrF2:Ho-APS films were prepared by casting from a solution at pH = 4.0–4.5. Scanning electron microscopy, energy-dispersive X-ray spectroscopy with element mapping, Fourier-transform infrared spectroscopy, X-ray diffraction methods confirmed homogeneous distribution of up-conversion particles in TOCNF matrices as well as the grafting of linear polysiloxanes via the condensation of silanol groups and OH-groups on the surface of TOCNF. Differential scanning calorimetry and thermogravimetry data confirmed an increase in thermal stability of the APS modified nanocomposite films obtained at pH = 4.0–4.5. Hydrophobic TOCNF/SrF2:Ho-APS nanocomposite films exhibited an intense red luminescence in the visible spectrum range (5I7 level excitation of Ho3+ ions with 1912 nm laser irradiation) as well as two-times higher laser damage threshold compared to unmodified TOCNF/SrF2:Ho films. TOCNF/SrF2:Ho-APS films can be used for visualization 2 μm laser radiation in medicine and long-distance atmosphere monitoring.

Polarized upconversion luminescence from a single LiLuF4:Yb3+/Er3+ microcrystal for orientation tracking

Polarized upconversion luminescence (UCL) of lanthanide-doped micro/nano-crystals has shown great promise in single-particle tracking and super-resolution bioimaging. However, because of the spectral line broadening and multiple sites of lanthanide in upconversion particles (UCPs), the crystal-field (CF) polarization components of UCL are usually undistinguishable. Herein, we report the linearly polarized UCL in LiLuF4:Yb3+/Er3+ single microcrystals with resolvable CF transition lines and a polarization degree up to 0.82. The CF levels and CF transition lines of Er3+, as well as their emission polarization anisotropy, are unraveled for the first time through low-temperature and high-resolution photoluminescence (PL) and UCL spectroscopies. By taking advantage of the well-resolved and highly-polarized CF transition lines of Er3+, we demonstrate the application of LiLuF4:Yb3+/Er3+ single microcrystals as anisotropic UCL probes for orientation tracking. These findings provide fundamental insights into the polarization anisotropy of UCL in lanthanide-doped single particles, thus laying a foundation for the future design of anisotropic luminescent probes towards versatile applications.

Ultrasensitive detection and removal of carbamazepine in wastewater using UCNPs functionalized with thin-shell MIPs

One of the issues that are currently emerging is the occurrence of pharmaceutical compounds including carbamazepine (CBZ) in environmental wastewater. We have developed upconversion particles (UCNPs@MIP) coated with new molecular imprinted polymer (thicknesses of 2.2 and 3 nm) through in situ photopolymerization by the internal green light of UCNPs upon photoexcitation at 980 nm. It has been utilized for ultrasensitive detection through fluorescence quenching of UCNPs emission by CBZ. The detection limits for CBZ with two different UCNPs@MIP were 28.5 and 40.0 pM (S/N = 3) with wide linear ranges and good correlation coefficients. Furthermore, the practical application of the sensors for the CBZ determination in wastewater and serum matrix was successfully investigated with acceptable recoveries of 98.2–104.2% and RSD less than 5%. Interestingly, the synthesized UCNPs@MIP revealed high selectivity with imprinting factors of 12.85 and 10.24 for MIP-a and MIP-b, respectively. Remarkably, UCNPs@MIP could be also blended with chitosan to form CS-MIP composite film as a simple removal technique of CBZ from wastewater samples with an adsorption capacity of 2.23 mg g−1 and removal percentage of 99.7% after 18 h. This method offers a novel facile strategy to develop UCNPs@MIP sensors for selective, sensitive, and accurate sensing of CBZ in environmental wastewater and biological samples.

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.

Double-layer metasurface boosts photon up-conversion

Up-conversion particles deposited on a double-layer metasurface leads to an impressive 2.7-fold enhancement in up-conversion photoluminescence.

Double-layer metasurface for enhanced photon up-conversion

We present a double-layer dielectric metasurface obtained by stacking a silicon nanodisk array and a silicon photonic crystal slab with equal periodicity on top of each other. We focus on the investigation of electric near-field enhancement effects occurring at resonant excitation of the metasurface and study its optical properties numerically and experimentally. We find that the major difference in multi-layer metasurfaces when compared to conventional single-layer structures appears to be in Rayleigh–Wood anomalies: they are split into multiple different modes, which are themselves spectrally broadened. As a proof of concept, we cover a double-layer metasurface with a lanthanide-doped up-conversion particle layer and study its interaction with a 1550 nm photoexcitation. We observe a 2.7-fold enhanced up-conversion photoluminescence by using the stacked metasurface instead of a planar substrate, although only around 1% of the up-conversion material is exposed to enhanced near fields. Two mechanisms are identified explaining this behavior: First, enhanced near fields when exciting the metasurface resonantly, and second, light trapping by total internal reflection in the particle layer when the metasurface redirects light into high angle diffraction orders. These results pave the way for low-threshold and, in particular, broadband photon up-conversion in future solar energy and biosensing applications.

Laser-induced assembly of biological cells and colloids onto a candle soot coated substrate

Recently, laser-induced heating assisted assembly of colloidal particles is emerging as a popular technique against direct light-assisted particle assembling methods. Herein, we demonstrate the trapping and assembly of yeast cells and upconversion particles at laser excitation intensities as low as 11 μW/μm2 via localized heating of non-plasmonic candle soot coated biocompatible polymer, polydimethylsiloxane. The thermal convective flow around the irradiation zone plays a vital role in trapping and assembling of the objects. The flow velocity profile is symmetrical around the irradiation zone, and the velocity increases drastically near the irradiation zone and with laser intensity. An increase in laser intensity leads to formation of an air bubble at the liquid-substrate interface and subsequent assembly of the objects at the interface. The tunneling of objects towards the irradiation zone across the barrier is demonstrated. Finally, with the localized laser-induced heating, the surface charge independent swarm of upconversion particle is shown, and the size and range of which found to be laser intensity dependent. With the wavelength-independent low power operation in the near-infrared range through simple optics, the results presented here may open avenues for a wide range of applications in diverse areas, including life sciences, colloidal science, nanoscience, photonics, and material science.

Systematic and detailed examination of NaYF4-Er-Yb-TiO2 photocatalytic activity under Vis–NIR irradiation: Experimental and theoretical analyses

Enhancing the efficiency of solar light utilization and understanding the acquired mechanism of photocatalytic reactions are the critical goals in the field of heterogeneous photocatalysis. To meet growing demands, the up-conversion particles (UCPs) have become an attractive perspective to extend the absorption spectrum of UV-active photocatalysts. The systematic experimental and theoretical study of the effects of UCPs on the photocatalytic activity of TiO2, and the investigation of its excitation mechanism are vital for understanding and optimizing the photocatalytic properties. Accordingly, hydrothermal process has been employed to manufacture visible light active NaYF4-Er-Yb-TiO2 photocatalyst in the present study. The UCPs have been located at the TiO2 crystal boundaries, where Er3+ and F− surface doping has been also observed. The predicted electronic structures of UCPs-TiO2 indicate that the formation of new Er-4f states within the band gap of TiO2 is the key factor of photocatalytic performance at Vis irradiation. Luminescence spectroscopy measurements reveal up-conversion energy transfer from Yb3+ to Er3+ ions in UCPs particles. Nevertheless, UCPs-TiO2 is not active under NIR irradiation, and the photocatalytic activity under Vis irradiation is not caused by OH, but rather by other forms of reactive oxygen species, such as O2− and OOH.

Upconversion emission studies of single particles

The optical detection setup, upconversion emissions and emerging microscopic/nanoscopic applications of single lanthanide nano- and microparticles are discussed in this review. • Principles of lanthanide upconversion emissions and the development status of upconversion nanoparticles. • Detection methods, steady-state and transient-state upconversion emission properties of single nanoparticles. • Emerging applications with high spatiotemporal resolution of single upconversion particles. • Future directions in terms of the photophysical properties and optical applications of single upconversion particles. Lanthanide-doped upconversion nanoparticles (UCNPs) have been gaining increasing research interests in chemistry, materials, optics, and interdisciplines due to their excellent photostability, adequate anti-Stokes emission efficiency, multicolor sharp-band emissions and tunable long emission lifetimes. Constructive applications on miniaturized optical devices, biomedicine, solar energy conversion, etc . have been demonstrated. Nonetheless, previous studies are mainly based on the properties from nanoparticle ensembles, which ignore the interparticle discrepancy in size, composition, surface status, optical properties, etc . Recently, with the development of optical detection with high sensitivity and spatial resolution, upconversion emission investigations step into a single particle level. This reveals intrinsic upconversion properties of UCNPs instead of leveling of particles. Here, we provide a critical review on the recent advances of upconversion in single nanoparticles and propose the perspectives of this emerging field. Specifically, we start by the introduction of detection methods of upconversion emissions in single nanoparticles. Subsequently, we summarized the very recent progress on photostability, steady-state and transient-state, polarized upconversion emissions, interparticle energy transfers as well as interdisciplinary studies on optical tracking, optical tweezer, lasing, and super-resolution nanoscopy of single UCNPs. Meanwhile, upconversion on a single microparticle is also included for the typical photophysical studies, such as optical waveguide and multiplexing. We further discussed future directions in terms of photophysical properties and microscopic/nanoscopic applications of upconversion in single particles. This review is expected to inspire investigations on disclosing intriguing upconversion properties of lanthanides and implanting UCNPs in advanced microscopic/nanoscopic applications.

Efficiency improvement of luminescent solar concentrators using upconversion nitrogen-doped graphene quantum dots

Luminescent solar concentrators (LSCs) incorporated with a large number of luminophores are used as an important trend which increases the efficiency of solar cells by concentrating solar energy onto photovoltaics (PVs). However, the main loss in LSC-PV devises results from the incomplete utilization of the solar spectrum. Extending the spectral absorption from UV–Vis into near-infrared (NIR) by means of upconversion particles, reduces the transmission loss of sub-band-gap photons with improved energy alignment. In this study, a new nitrogen-doped graphene quantum dot (N-GQD) possessing upconversion photoluminescence (UCPL), single color emission in UV–Vis–NIR region has been introduced. Large stocks shift of newly synthesized GQDs that is more than 100 nm reduces reabsorption losses significantly. Photoluminescence (PL) quantum yield is measured to be 65%. Under solar radiation, the optical features of N-GQDs as absorbers/emitters in polymethyl methacrylate (PMMA) is studied. Our results demonstrate that GQDs-LSC attached to a perovskite solar cell could enhance efficiency. The GQDs-LSCs reaches the power conversion efficiency (PCE) more than 4.3 times of PMMA-PV devise. Although the use of N-GQDs hybrid in LSCs for its upconversion feature is at an initial research step, the results prove that it provides a promising way for low cost and nonhazardous solar energy.

Effect of Cr3+ and alkaline-earth metal ions co-doping on the enhancement of upconversion luminescence in β-NaYF4:Yb3+/Er3+ microparticles

To investigate the optical properties of rare earth upconversion particle, the Cr3+ and alkaline-earth ions (Mg2+ or Ca2+) co-doped β-NaYF4:Yb3+/Er3+ upconversion microparticles (UCMPs) were synthesized via a facile hydrothermal method. The influences of co-doping ions and their concentrations on crystal structure, particle morphology and optical properties were thoroughly investigated by XRD, SEM, FT-IR spectra, UV–VIS-NIR absorption spectra and photoluminescence spectra. And the effects of the two kinds of impurity ions co-doping on the UC particle growth were studied. We found that luminescence quenching could be inhibited by using Cr3+ and Mg2+ co-doping due to the asymmetrical ion arrangement around activator. However, the Cr3+ and Ca2+ co-doping was found to quench the upconversion luminescence (UCL), and the possible mechanism was suggested. These discoveries lead to new insights into the quenching effect and new strategy to design UCMPs for better luminescence performance.