Upconversion Luminescence Emission Research Articles

Microwave-assisted solvothermal synthesis and upconversion luminescence of CaF2:Yb3+/Er3+ nanocrystals

Water-dispersible CaF2 and Yb3+/Er3+ codoped CaF2 (CaF2:Yb3+/Er3+) nanocrystals with different sizes and different Yb3+ and Er3+ dopant concentrations were synthesized using ionic liquid 1-n-butyl-3-methyl imidazolium tetrafluoroborate as a fluorine source by the rapid microwave-assisted solvothermal method. It was found that the morphology, size and crystallinity of CaF2:Yb3+/Er3+ nanocrystals could be adjusted by using adenosine 5′-triphosphate disodium salt (ATP). Yb3+ and Er3+ ions were doped into CaF2 nanocrystals to enable upconversion luminescence emission, and the as-prepared CaF2:Yb3+/Er3+ samples exhibited upconversion luminescence upon excitation at 980nm. Confocal laser scanning microscopy images showed that the CaF2:Yb3+/Er3+ nanocrystals could be used for efficient labeling of human gastric carcinoma cells. Moreover, in vitro cytotoxicity experiments indicated that the as-prepared CaF2:Yb3+/Er3+ nanocrystals had essentially little cytotoxicity. These results indicate that the as-prepared CaF2:Yb3+/Er3+ nanocrystals are promising for the application as a luminescent label material in biological imaging.

An upconversion nanocomposite for fluorescence resonance energy transfer based cholesterol-sensing in human serum.

Upconversion nanophosphors (UCNPs) are extremely useful for analytical applications, since they display a high signal-to-noise ratio, and their photobleaching can be ignored. Herein, a novel upconversion nanocomposite composed of β-cyclodextrin (β-CD) derivative modified UCNPs and rhodamine B (RB) was prepared for the detection of cholesterol (Cho). The upconversion luminescence (UCL) emission can serve as a Cho-sensing signal by an effective fluorescence resonance energy transfer (FRET) process, using UCNPs as the donor and RB as the quencher. The sensor for Cho detection in human serum shows excellent sensitivity and selectivity, which has the potential for clinical applications in the analysis of other biological and environmental samples.

Near-infrared-light mediated ratiometric luminescent sensor for multimode visualized assays of explosives.

The development of a portable and easy-to-use device for the detection of explosives with high sensitivity and selectivity is in high demand for homeland security and public safety. In this study, we demonstrate miniaturized devices depending on the upconversion ratiometric luminescent probe for point-of-care (POC) assay of explosives with the naked-eye. When the PEI-coated upconversion nanoparticles (UCNPs) selectively bonded to 2,4,6-trinitrotoluene (TNT) explosives by the formation of Meisenheimer complex, the formed of UCNP-Meisenheimer complexes show turned visible multicolor upconversion luminescence (UCL) on account of TNT-modulating Förster resonance energy transfer process under near-infrared excitation. With UCL emission at 808 nm as internal standard and ratiometric UCL at 477 nm to that at 808 nm (I477/I808) as output signal, the probe can simultaneously meet the accuracy for TNT explosives quantitative analysis. In addition, this easy-to-use visual technique provides a powerful tool for convenient POC assay of rapid explosives identification.

Enhanced upconversion luminescence and single-band red emission of NaErF4 nanocrystals via Mn2+ doping

In this paper, the monodispersed NaErF4:Yb, Mn nanoparticles (NPs) were successfully synthesized by a simple and mild solvothermal method. The as-prepared NPs were characterized by X-ray diffraction, transmission electron microscopy, and spectrophotometer. The crystal phase, size, morphology, and upconversion (UC) properties of these NPs can be readily tuned by doping Mn2+. With increasing Mn2+ contents, the crystal phase of NaErF4:Yb NPs was transferred from hexagonal to cubic, and then a new orthorhombic phase NaMn3F10 appeared. The morphology of NaErF4:Yb was tuned from nanodisks to nanocubes and then to large nanoflakes with increasing Mn2+ dopant contents. Moreover, the UC luminescence (UCL) intensity can be enhanced by increasing Mn2+ content. Interestingly, single-band red emission can be achieved when the Mn2+ content reaches 20%. This is mainly ascribed to the efficient energy transfer between Er3+ and Mn2+. The enhanced UCL intensity and single-band red UCL make these NaErF4:Yb/Mn NPs ideal probes for optical bioimaging owing to the low tissue absorption and deep tissue penetration of red light.

Multicolor frequency upconversion luminescence in Eu3+/Tb3+/Yb3+-codoped fluorogermanate glass excited at 980 nm

Glasses80GeO3:10PbF2:10CdF2 triply-doped with europium, terbium, and ytterbium phosphors were synthesized and the energy up-conversion luminescence emission properties investigated as a function of NIR excitation power, rare-earth ions content combination, and glass phosphor composition. Multicolor visible luminescence with main emissions peaked around 490, 545, 590, 610, 650, and 700nm was observed when samples were excited by a diode laser at 980nm. The up-conversion excitation mechanism for both Eu3+, and Tb3+ excited-state emitting levels was achieved via phonon-assisted cooperative energy-transfer from pairs of excited Yb3+ ions. White-light emission with CIE-1931 coordinates in the region of low color correlated temperature was obtained for appropriate combination of rare-earth ions content.

Emission behaviors of Yb2O3 nanoparticles pumped by 980nm laser at different power densities

Abstract Yb2O3 nanoparticles synthesized via Pechini type sol-gel method were characterized by TEM, SAED, EDS, XRD, SEM and Raman spectrometer. Their emission properties were recorded by a fluorescence spectrophotometer with a 980 nm laser as the excitation source. These spectral results indicate that there are two optical bistable emissions at low/high laser power densities, i.e. Yb3+–Yb3+ dimer cooperative upconversion luminescence and thermal emission. Thus, Yb2O3 nanoparticles might be regarded as a candidate for intrinsic optical bistability.

Rhodamine‐Modified Upconversion Nanophosphors for Ratiometric Detection of Hypochlorous Acid in Aqueous Solution and Living Cells

Hypochlorous acid (HOCl), a reactive oxygen species (ROS) produced by myeloperoxidase (MPO) enzyme-mediated peroxidation of chloride ions, acts as a key microbicidal agent in immune systems. However, misregulated production of HOCl could damage host tissues and cause many inflammation-related diseases. Due to its biological importance, many efforts have been focused on developing fluorescent probes to image HOCl in living system. Compared with those conventional fluorescent probes, up-conversion luminescence (UCL) detection system has been proven to exhibit a lot of advantages including no photo-bleaching, higher light penetration depth, no autofluorescence and less damage to biosamples. Herein, we report a novel water-soluble organic-nano detection system based on rhodamine-modified UCNPs for UCL-sensing HOCl. Upon the interaction with HOCl, the green UCL emission intensity in the detection system were gradually decreased, but the emissions in the NIR region almost have no change, which is very important for the ratiometric UCL detection of HOCl in aqueous solution. More importantly, RBH1-UCNPs could be used for the ratiometric UCL visualization of HOCl released by MPO-mediated peroxidation of chloride ions in living cells. This organic-nano system could be further developed into a novel next-generation imaging technique for bio-imaging HOCl in living system without background noise.

Folic acid-functionalized up-conversion nanoparticles: toxicity studies in vivo and in vitro and targeted imaging applications.

Folate receptors (FRs) are overexpressed on a variety of human cancer cells and tissues, including cancers of the breast, ovaries, endometrium, and brain. This over-expression of FRs can be used to target folate-linked imaging specifically to FR-expressing tumors. Fluorescence is emerging as a powerful new modality for molecular imaging in both the diagnosis and treatment of disease. Combining innovative molecular biology and chemistry, we prepared three kinds of folate-targeted up-conversion nanoparticles as imaging agents (UCNC-FA: UCNC-Er-FA, UCNC-Tm-FA, and UCNC-Er,Tm-FA). In vivo and in vitro toxicity studies showed that these nanoparticles have both good biocompatibility and low toxicity. Moreover, the up-conversion luminescence imaging indicated that they have good targeting to HeLa cells and can therefore serve as potential fluorescent contrast agents.

Cyclometallated ruthenium complex-modified upconversion nanophosphors for selective detection of Hg2+ions in water

Upconversion detection nanocomposites were assembled for the selective luminescent detection of mercury ions in water. A hydrophobic cyclometallated ruthenium complex [Ru(II)(bpy)2(thpy)]PF6 (abbreviated as Ru1; bpy = 2,2'-bipyridine and thpy = 2-(2-thienyl)pyridine) is employed as a chemodosimeter to assemble on amphiphilic polymer-coating upconversion nanophosphors (UCNPs) based on the hydrophobic-hydrophobic interaction. Upon addition of Hg(2+), the nanocomposite not only exhibits a remarkable color change from deep-red to yellow, but also an enhanced upconversion luminescence (UCL) emission by hindering the luminescent resonance energy transfer (LRET) process from the upconversion emission of UCNPs to Ru1. Using the ratiometric UCL emission as a detection signal, the detection limit of Hg(2+) for this nanoprobe in aqueous solution is 8.2 ppb, which is much lower than that (329 ppb) determined by UV/Vis technology. Such an Hg(2+)-tunable LRET process provides a general strategy for fabricating a water-soluble upconversion-based nanoprobe for some special analyte.

ChemInform Abstract: Upconversion‐Nanophosphor‐Based Functional Nanocomposites

AbstractReview: < 100 refs.

Luminescence investigation of Yb3+/Er3+ codoped single LiYF4 microparticle

Tetragonal phase LiYF4:Yb3+/Er3+ microparticles are synthesized via facile hydrothermal method. Single LiYF4 microparticle is excited with IR laser at 980nm in a confocal setup, and strong green and weak red emissions are observed. It is found that single LiYF4:Yb3+/Er3+ microparticle with sub-structure presents stronger upconversion luminescence emission and smaller intensity ratio of red to green emission than that from LiYF4:Yb3+/Er3+ microparticle with no sub-structure. The possible mechanism, the influence of particle size and the existence of EDTA on the upconversion luminescence emission are investigated. The current study suggests that the luminescence observation with single micropaticle can effectively avoid the influence of environment and neighbor particles, which is important for investigating the luminescence properties of micro- or nano-crystals and for extending their application.

Upconversion luminescence imaging of cells and small animals

Upconversion luminescence (UCL) is an anti-Stokes process whereby low-energy photons are converted to higher-energy ones. UCL imaging for cells and animal tissues has attracted substantial attention in recent years because of the unique abilities of upconversion materials, which can minimize the background interference from the autofluorescence of biosamples and enhance tissue penetration. This protocol describes a step-by-step guide for the fabrication of UCL probes, including lanthanide-based upconversion nanoparticles (Ln-UCNPs) with a particle size of ∼20 nm (NaYF4/NaLuF4: Yb, Er/Tm) and triplet-triplet annihilation-based UCNPs (TTA-UCNPs) with a particle size of ∼10 nm (palladium octaethylporphyrin as sensitizer and 9,10-diphenylanthracene as annihilator). We also describe the characterization of the UCL nanoprobes (via transmission electron microscopy and UCL emission spectroscopy) and functionalization (via silica coating and ligand exchange), as well as applications for UCL bioimaging of living cells (HeLa cells) and small animals (nude mice and Kunming mice). The setup of a laser-scanning UCL microscope and a UCL imaging system is also presented. Compared with a normal imaging setup, we adopted longer-wavelength excitation lasers and short-pass filters. The synthesis of hydrophilic UCNP for application in UCL bioimaging requires ∼15 d.

Upconversion Luminescence and Optical Studies of Nd3+ in Bismuth Borate Glasses

Neonymium doped bismuth borate glasses with composition 50Bi2O3 : (50-x)B2O3: xNd2O3 (where x = 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) have been prepared by melt quenching technique. The optical and upconversion luminescence properties of glasses were investigated. The nine absorption peaks were observed, correspond with Nd3+ energy level in glass. The optical band gap decreased with increasing Nd2O3 concentration due to the increase of non-bridging oxygen (NBOs) in glass matrix. The upconversion luminescence emission spectra shows peak at 393 nm, assign to 4D3/24I11/2 transition.

Upconversion‐Nanophosphor‐Based Functional Nanocomposites

Upconversion nanophosphors have the ability to generate visible or near-infrared (NIR) emissions under continuous-wave NIR excitation. Utilizing this special photoluminescent properties, upconversion nanophosphors can be used as key components in complex nanocomposites for a wide range of applications. This review summarizes the basic concept, fabrication strategy, and typical application of upconversion-nanophosphor-based functional nanocomposites. The motivation to design these structures comes from the potential applications in detection, multi-modality bioimaging, and NIR light-induced therapy, as well as the tuning of the upconversion luminescence emissions. This review will give a brief summary of this rapidly developing field, and provide guidance to design and to fabricate new nanocomposites based on upconversion nanophosphors.

Ultraviolet and visible up-conversion luminescence of Er3+/Yb3+ co-doped CaF2 nanocrystals in sol–gel derived glass-ceramics

Glass-ceramics containing Er3+/Yb3+ codoped CaF2 nanocrystals have been prepared by using the controlled crystallization above 650°C of the (Yb3+/Er3+) codoped CaF2–SiO2 xerogels. X-ray diffraction and scanning electron microscopy data have revealed the formation of CaF2 nanocrystals of about 16nm size. For pumping at 973nm, this glass-ceramics shows, besides green and red up-conversion luminescence, violet (at ∼408nm) and near-ultraviolet emission (at ∼380nm). The mechanisms responsible for the upconversion luminescence are presented and discussed. The fluorescence lifetimes of the metastable levels responsible for violet, green and red luminescence are measured and their quantum efficiencies are estimated.

Bifunctional Gd2O3:Er3+ particles with enhanced visible upconversion luminescence

This study examined the enhanced upconversion luminescence emission of bimodal Gd2O3:Er3+ particles by codoping with a trace amount of Li+ ions. Gd2O3:Er3+/Li3+ composite particles with enhanced upconversion luminescence emission were synthesized by using a simple urea homogeneous precipitation method. The effect of the particle size and Er3+/Li+ concentration ratio on the structural, morphological and optical properties of Gd2O3:Er3+/Li+ particles were studied systematically by X-ray powder diffraction, field emission scanning electron microscopy and room temperature photoluminescence. Strong upconversion eye-visible green light emission was observed from the Gd2O3:Er3+/Li+ particles under continuous near-infrared pump excitation from a commercially available diode laser. Monodisperse bimodal Gd2O3:Er3+/Li+ particles show a good potential for biomedical and solid state lighting applications.

A General Strategy for Biocompatible, High-Effective Upconversion Nanocapsules Based on Triplet–Triplet Annihilation

A general strategy for constructing high-effective upconversion nanocapsules based on triplet-triplet annihilation (TTA) was developed by loading both sensitizer and annihilator into BSA-dextran stabilized oil droplets. This strategy can maintain high translational mobility of the chromophores, avoid luminescence quenching of chromophore by aggregation, and decrease the O2-induced quenching of TTA-based upconversion emission. Pt(II)-tetraphenyl-tetrabenzoporphyrin (PtTPBP) and BODIPY dyes (BDP-G and BDP-Y with the maximal fluorescence emission at 528 and 546 nm, respectively) were chosen as sensitizer/annihilator couples to fabricate green and yellow upconversion luminescent emissive nanocapsules, named UCNC-G and UCNC-Y, respectively. In water under the atmospheric environment, interestingly, UCNC-G and UCNC-Y exhibit intense upconversion luminescence (UCL) emission (λex = 635 nm) with the quantum efficiencies (ΦUCL) of 1.7% and 4.8%, respectively, whereas very weak UCL emission (ΦUCL < 0.1%) was observed for the corresponding previous reported SiO2-coating nanosystems because of aggregation-induced fluorescence quenching of annihilators. Furthermore, application of theses upconversion nanocapsules for high-contrast UCL bioimaging in vivo of living mice without removing the skin was demonstrated under 635-nm excitation with low power density of 12.5 mW cm(-2).

Multifunctional photosensitizer-conjugated core–shell Fe3O4@NaYF4:Yb/Er nanocomplexes and their applications in T2-weighted magnetic resonance/upconversion luminescence imaging and photodynamic therapy of cancer cells

Due to non-invasive deep imaging and therapy, multifunctional agents of magnetic resonance (MR)/upconversion luminescence (UCL) imaging and photodynamic therapy (PDT) play an important role in clinical diagnosis and treatment of cancers, and also in the assessment of therapy effect. In this paper, tetra-sulfonic phthalocyanine aluminium (AlPcS4) photosensitizers-conjugated Fe3O4@NaYF4:Yb/Er (NPs-AlPcS4) nanocomplexes were synthesized for the T2-weighted MR/UCL imaging and PDT of cancer cells. The PEG-coated Fe3O4@NaYF4:Yb/Er nanoparticles (NPs) with a core–shell structure showed strong T2-weighted MR relaxivity (r2 = 42.131 mM−1 s−1) and UCL emission in the visible region (the bands at about 654–674 nm, 545 nm and 524 nm), and were conjugated successfully with AlPcS4 photosensitizer by electrostatic interaction. By direct observation of XFM and staining with Prussian blue, the element distribution and location of NPs in MCF-7 cells were characterized, respectively. Under irradiation from a 980 nm laser, the death ratio of MCF-7 cells incubated with NPs-AlPcS4 nanocomplexes could be up to about 70%. The results indicated that the as-prepared NPs-AlPcS4 nanocomplexes would be a potential candidate as multifunctional nanoprobes for the dual-modal T2-weighted MR/UCL imaging and PDT of cancers in the future.

Comparative Investigation of Optical Properties in Tm&lt;sup&gt;3&lt;/sup&gt;&lt;sup&gt;+&lt;/sup&gt;/Er&lt;sup&gt;3&lt;/sup&gt;&lt;sup&gt;+&lt;/sup&gt;/Yb&lt;sup&gt;3&lt;/sup&gt;&lt;sup&gt;+&lt;/sup&gt; Co-Doped Oxyfluoride Tellurite and Germanate Glasses

Tm3+/Er3+/Yb3+co-doped oxyfluoride tellurite and germanate glasses have been synthesized by conventional melting method. Intense up-conversion (UC) luminescence emissions were simultaneously observed under 980 nm excitation at room temperature in two glasses. The possible UC mechanisms are discussed and estimated. However, in the studied Tm3+/Er3+/Yb3+co-doped oxyfluoride glasses, tellurite glass showed weaker UC emissions than germanate glass, which is inconsistent with the prediction from the difference of maximum phonon energy between oxyfluoride tellurite and germanate glasses. Absorption spectrum and Raman spectroscopy were employed to investigate the origin of the difference in UC luminescence in two glasses. Our results confirm that, besides the maximum phonon energy, the phonon density of host glasses is another important factor in determining the UC efficiency.

Highly sensitive and selective novel core–shell molecularly imprinted polymer based on NaYF4: Yb3+, Er3+ upconversion fluorescent nanorods

A novel core–shell molecularly imprinted polymer based on β-NaYF4: Yb3+, Er3+ upconversion fluorescent nanoparticles (UCNPs@MIP) has been successfully synthesized, which has a homogeneous polymer film, shows thermal stability, exhibits excellent near-infrared upconversion luminescence emission and sensitivity and selectivity towards analytes.