Upconversion Particles Research Articles

Pulsed periodic laser excitation of upconversion luminescence for deep biotissue visualization

Emission spectral properties and quantum efficiency of upconversion particles NaYF4, SrF2, LaF3, BaF2 и CaF2, doped with rare earth ions pair Yb3+–Er3+ were studied using continuous wave (CW) and pulsed periodic excitation modes in the near infrared (NIR) spectral range. Analysis of the obtained results showed that the intensity ratio of upconversion luminescence in green and red spectral ranges depends on excitation pulse duration. Thus, by changing the pulse duration the spectral properties of upconversion luminescence can be controlled. Crystals with higher phonon energy are more sensitive to the change of pumping mode. Interpretation of results was performed on the rate equation model basis. Using numerical methods for all energy levels involved in the upconversion process the population and depopulation dynamics were obtained with respect to the duration of the excitation pulses. It was shown that about 30 ms was required for the complete population of 4F9/2 state, from which the luminescence in the red spectral range occurs. When the pulse duration was less than 30 ms, the 4F9/2 population did not reach a steady state and the intensity of the luminescence in the red part of the spectrum was reduced. The theoretical dependence of the upconversion luminescence intensity in the green and red ranges of the excitation pulse duration for NaYF4:Yb0.2–Er0.02 composition was obtained and demonstrates good agreement with the experimental results.

Ultraviolet upconversion enhancement in triply doped NaYF4:Tm3+, Yb3+ particles: The role of Nd3+ or Gd3+ Co-doping

Upconversion (UC) particles are currently under intensive investigation, normally for their visible instead of ultraviolet (UV) light luminescence under near-infrared (NIR) irradiation. As a commonly studied host, NaYF4 in particular is known to have low phonon energy and high UC efficiency. Here, we present our work on enhancing UC luminescence in the UV region by adding a third dopant into a binary-doped NaYF4:Yb3+,Tm3+ host. More specifically, neodymium (Nd3+) or gadolinium (Gd3+) ions was co-doped into parent NaYF4:20mol%Yb3+,0.5mol%Tm3+ UC particles to enhance their UV UC luminescence. Experimental results demonstrated that these particles exhibited the highest degree of UV UC enhancements when co-doped with 0.05mol% Nd3+ or 2.0mol% Gd3+, expanding the potential of this type of materials into many possible applications by directly converting NIR irradiation into UV light. Fundamentally, the UV UC emission dependence of these triply doped NaYF4:Yb3+,Tm3+ particles with different Nd3+ and Gd3+ doping concentrations was investigated in terms of ground state absorption, excited state absorption and energy transfer UC mechanisms.

Luminescence Monitoring of Temporal Changes and Efficiency of Tissue Optical Clearing by NIR-Excited Upconversion Particles

Luminescence Monitoring of Temporal Changes and Efficiency of Tissue Optical Clearing by NIR-Excited Upconversion Particles

Upconverter-powered oxygen sensing in electrospun polymeric bilayers

Optical oxygen sensors based on luminescent quenching are attractive as they are easily miniaturized, offer excellent sensitivity, and in the appropriate vehicle exhibit no cytotoxicity. However, these sensors must be energized by violet or blue wavelengths to report variations in oxygen content. These wavelengths experience high levels of absorption and scattering in biological tissue. Upconverting particles (UCPs) sidestep this limitation due to their ability to sequentially absorb two or more longer wavelength photons to emit a single, shorter wavelength photon. In this work, UCPs were utilized to emit blue light upon near infrared (NIR) absorption. A key advantage is that NIR light efficiently penetrates tissue barriers associated with potential biomedical applications. A layer of polycaprolactone (PCL) fibers containing Ru(dpp)3Cl2 was electrospun directly on top of a layer of fibers containing UCPs. We chose a bilayer configuration as it allowed direct examination of the ‘handshake’ interaction and investigation of significant design issues. Configurational aspects of the bilayer format were studied. Additionally, gaseous oxygen sensing following NIR excitation was confirmed. These upconverter-powered sensors were found to have a rapid response ( <0.25s).

Extremely deep photopolymerization using upconversion particles as internal lamps

More than 10 centimeters of photopolymerization depth is obtained using upconversion nanoparticles as internal lamps.

PEG and PVP assisted solvothermal synthesis of NaYF4:Yb3+/Er3+ up-conversion nanoparticles

Owing to their unique optical properties, up-converting rare earth fluorides have attracted extensive attention in recent years. Varieties of synthesis procedures which generate nano- and micro-crystals with controllable compositions have been reported. In the vast majority, surfactants, complexing agents and solvents play essential role in controlling particles morphology and surface characteristics. Here we report on a rapid solvothermal synthesis (200°C, 2h) of either PEG or PVP capped NaYF4:Yb3+/Er3+ particles. Their structural, morphological and luminescence characteristics have been studied based on X-ray powder diffractometry (XRPD), Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM) and photoluminescence measurements. Both polymers proved to be a good structure directing agents enabling generation of the well crystalline polymer coated up-converting particles with efficient emissions in visible spectrum. It was shown that generation of the hexagonal P63/m β-NaYF4:Yb3+/Er3+ phase with the most efficient green emission (CIE 0.31, 0.66) is enhanced when PVP is used during synthesis, while promotion of the cubic Fm-3m α-NaYF4:Yb3+/Er3+ phase that has a yellowish spectral output (CIE 0.41, 0.56) was observed in the particles produced in the presence of PEG. Beneficial effect on the luminescence intensity was observed with additional particles annealing in argon atmosphere.

Upconversion Particle as a Local Luminescent Brownian Probe: A Photonic Force Microscopy Study

Near-infrared (NIR) light sensitive lanthanide-doped NaYF4 upconversion particles (UCPs) are gaining increasing attention as local probes in biomedical applications. Here, we implemented a photonic force microscope (PFM) to manipulate and study the optical properties of trapped single UCPs, beta-NaYF4:Yb,Er. In particular, we focused on the mechanisms of the optical trapping of nonspherical UCPs of different sizes, in the range 0.5-2 mu m, as well as on their upconversion photoluminescence (UCL) properties under excitation with the strongly focused laser beam (lambda = 1064 nm) of the PFM, operating at power densities up to 14.7 MW cm(-2). A careful analysis of UCL under such conditions points to three emission peaks at 469, 503.6, and 616.1 nm, which were enhanced by the high laser power density. The analysis of Brownian motion was used to quantify the thermal fluctuations of the particle inside the optical trap as well as the particle sizes and optical forces acting in the two dimensions perpendicular to the optical axis. A steep dependence of UCL as a function of the particle diameter was found for UCPs having sizes smaller than the focal spot (similar to 900 nm) of the NIR laser.

Interactions of CT DNA with hexagonal NaYF4 co-doped with Yb3+/Tm3+ upconversion particles

The interaction of UCPs with CT DNA are studied in detail by zeta potential, Energy dispersive spectrometer (EDS) spectroscopy, Thermogravimetric (TGA) analysis, DNA melting determination and various spectroscopic techniques including Ultraviolet–Visible (UV–Vis) absorption, fluorescence, circular dichroism (CD), Fourier transform infrared (FTIR) and Raman spectroscopy. The results indicate that CT DNA can assemble on the surface of UCPs mainly by relative stronger hydrophobic force and electrostatic binding, and the predominant interaction site is the deoxyribosyl phosphate backbone of CT DNA. Moreover, after interacting with UCPs, the double helix structure of DNA is undamaged.

Photon Up-Conversion with Lanthanide-Doped Oxide Particles for Solar H2 Generation

Up-conversion (UC) of infrared (IR) photons into visible radiation constitutes a promising strategy to enhance the light harvesting efficiency of photovoltaic and photoelectrochemical devices. In the present study, we integrate Er3+/Yb3+-codoped yttrium oxide (Y2O3) submicrometric particles with outstanding up-conversion properties into mesoporous titanium oxide (TiO2) structures sensitized with cadmium selenide (CdSe) for solar hydrogen generation. We demonstrate that the incorporation of these up-converting particles (UCP) leads to effective H2 generation with IR photons. Moreover, based on the analysis of the emission lifetimes, we show that the optical interaction between the emitting UCPs and the CdSe absorber occurs via a radiative emission–reabsorption process. The low cost and toxicity and excellent chemical and thermal stability of our UC phosphors allow envisaging them as real candidates for the new generation of long-term photoelectrochemical devices for solar H2 generation.

A simple modification of near-infrared photon-to-electron response with fluorescence resonance energy transfer for dye-sensitized solar cells

Upconversion (UC) Er, Yb-YF3 is introduced into dye-sensitized solar cells (DSSC) through a simple method to investigate the effect of UC particles in photoanode. The utilization of UC phosphor can significantly improve the photocurrent of the cells under both infrared irradiation and sunlight. Fluorescence resonance energy transfer (FRET) and luminescence-mediated energy transfer between UC-YF3 and N719 dye are explored as the main contribution that UC-YF3 made to DSSC. With the multi-efforts of UC-YF3, power conversion efficiency (PCE) of DSSC is improved from 5.18% to 6.22%. Besides, Electron transfer between UC-YF3 and TiO2 is found after sintered at 450 °C, and the PCE value of DSSC is improved further (5.34% → 6.76%). In addition, we explore that UC-YF3 can serve as a scattering material to increase the light absorption capability of the cells and increase the photocurrent of the cells under simulated sunlight irradiation.

Development of luminescent pH sensor films for monitoring bacterial growth through tissue.

Although implanted medical devices (IMDs) offer many benefits, they are susceptible to bacterial colonization and infections. Such infections are difficult to treat because bacteria could form biofilms on the implant surface, which reduce antibiotics penetration and generate local dormant regions with low pH and low oxygen. In addition, these infections are hard to detect early because biofilms are often localized on the surface. Herein, an optical sensor film is developed to detect local acidosis on an implanted surface. The film contains both upconverting particles (UCPs) that serve as a light source and a pH indicator that alters the luminescence spectrum. When irradiated with 980 nm light, the UCPs produce deeply penetrating red light emission, while generating negligible autofluorescence in the tissue. The basic form of the pH indicator absorbs more of upconversion luminescence at 661 nm than at 671 nm and consequently the spectral ratio indicates pH. Implanting this pH sensor film beneath 6-7 mm of porcine tissue does not substantially affect the calibration curve because the peaks are closely spaced. Furthermore, growth of Staphylococcus epidermidis on the sensor surface causes a local pH decrease that can be detected non-invasively through the tissue.

Synthesis of Yb/Er Doped NaYF&lt;sub&gt;4&lt;/sub&gt; Nanoparticles with Intense Green up-Conversion Emission

The luminescent rare-earth nanomaterials have great potential in the biological and biomedical applications due to their unique optical characteristics. An infrared-to-visible up-conversion NaYF4: Yb3+, Er3+nanoparticle was synthesized by hydrothermal method. More intense green up-conversion luminescence was obtained due to using citrate as a chelator. Different sizes of up-conversion particles (UCNPs) in the range of 40 to 1000 nm were available by adjusting the molar ratio of fluoride to Ln3+. The UCNPs were coated by silica and functionalized with amino groups for a conjugation with biomolecules. The UCNPs prepared might be promising for bioassay, bioimaging and diagnostics, especially in vivo environment and living cells.

Upconverting Nanoparticles

Upconversion (UC) refers to nonlinear optical processes in which the sequential absorption of two or more photons leads to the emission of light at shorter wavelength than the excitation wavelength (anti-Stokes type emission). In contrast to other emission processes based on multiphoton absorption, upconversion can be efficiently excited even at low excitation densities. The most efficient UC mechanisms are present in solid-state materials doped with rare-earth ions. The development of nanocrystal research has evoked increasing interest in the development of synthesis routes which allow the synthesis of highly efficient, small UC particles with narrow size distribution able to form transparent solutions in a wide range of solvents. Meanwhile, high-quality UC nanocrystals can be routinely synthesized and their solubility, particle size, crystallographic phase, optical properties and shape can be controlled. In recent years, these particles have been discussed as promising alternatives to organic fluorophosphors and quantum dots in the field of medical imaging.

反应物浓度对NaYF4∶Yb3+,Tm3+晶相的影响

A series of NaYF4∶20%Yb3+,1%Tm3+ upconversion particles(UCPs) with different morphology were prepared by the facile hydrothermal approach.The morphology,crystalline phase and optical properties were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD) and luminescent spectra.XRD patterns and SEM images showed that the UCPs crystalline phase tansformed from cubic phase to hexagonal phase by controlling the reactants concentration.Pumped with 980 nm diode laser,the UCPs emitted bright violet/blue upconversion luminescence.By analyzing the effect of reactants concentration on the products crystalline phase,the crystal growth mechanism of NaYF4 was studied in detail.Significantly,our research work would provide more experimental data for controlling the crystalline phase of the upconversion luminescent materials.

Two-Photon Excitation Fluorescence Resonance Energy Transfer with Small Organic Molecule as Energy Donor for Bioassay

A fluorescence resonance energy transfer (FRET) model using two-photon excitable small organic molecule DMAHAS as energy donor has been constructed and tried in an assay for avidin. In the FRET model, biotin was conjugated to the FRET donor, and avidin was labeled with a dark quencher DABS-Cl. Binding of DABS-Cl labeled avidin to biotinylated DMAHAS resulted in the quenching of fluorescence emission of the donor, based on which a competitive assay for free avidin was established. With using such donors that are excited in IR region, it is capable of overcoming some primary shortcomings of conventional one-photon FRET methods, especially in bioassays, such as the interference from background fluorescence or scattering light, the coexcitation of the energy acceptor with the donor. And such small molecules also show advantages over inorganic up-converting particles that also give anti-Stokes photoluminescence and have been applied as FRET donor recently. The results of this work suggest that two-photon excitable small molecules could be a promising energy donor for FRET-based bioassays.

Design of a Highly Sensitive and Specific Nucleotide Sensor Based on Photon Upconverting Particles

We have designed and developed a novel sensor that reports the presence of specific nucleic acids in solutions, based on photon upconverting particles. The significantly high signal-to-noise ratio of photon upconverting particles leads to high sensitivity of the sensor. The sensor does not suffer from photobleaching. It also displays high specificity and self-calibrating capability. We expect nucleotide sensors of this type to be effective for applications in both DNA/RNA detection and protein-DNA/RNA interaction studies.