Down-conversion Fluorescence Research Articles

UV protection from cotton fabrics finished with boron and nitrogen co-doped carbon dots

Ultraviolet (UV)-protective cotton fabrics are necessary for outdoor cotton clothing. In this study, boron and nitrogen co-doped carbon dots (BN-CD) are synthesized by one-pot hydrothermal carbonization, and consequently served as UV-absorber for cotton textiles. Fourier transform infrared, transmission electron microscope, scanning electron microscope and UV–Vis spectroscopy are used to characterize the structure and properties of BN-CDs and cotton fabrics finished by BN-CDs. The UV protection property and laundering durability of treated cotton fabrics are also measured. The results show that as-prepared BN-CD has high fluorescence and down-conversion fluorescence emission. The cotton fabric finished by the BN-CD and poly(vinyl alcohol) exhibits a UV transmittance of less than 4% in the range of 280–400 nm, a UV protection factor value of up to 38.6 and good laundering durability, indicating a promising potential of BN-CD as UV absorbers for finishing cotton fabrics.

Multimodal Cancer Theranosis Using Hyaluronate‐Conjugated Molybdenum Disulfide

Among various 2D nanomaterials, molybdenum disulfide (MoS2 ) exhibits unique visible photoluminescence with high absorption at the near-infrared (NIR) range. Despite these optical properties, the efforts to use MoS2 nanomaterials for optical imaging and photothermal therapy are hampered by their instability and low intracellular delivery efficiency. Multifunctional MoS2 conjugated with hyaluronate (HA) for cancer theranosis is reported herein. HA facilitates the delivery of MoS2 to tumor cells by the HA-receptor mediated endocytosis. In BALB/c nude mice inoculated with a colorectal cancer cell line of HCT116, HA-MoS2 conjugates appear to be accumulated in the primary tumor at a content more than that in the liver and kidney. The disulfide bonding between MoS2 and thiolated HA seems to degrade in the cytoplasm, releasing MoS2 sheets in stacks and enhancing luminescence efficiency. The HA-MoS2 conjugates are readily detected via photoacoustic imaging as well as upconversion and downconversion fluorescence imaging. With NIR light illumination, HA-MoS2 conjugates enable highly effective photothermal tumor ablation. All these results confirm the promising potential of HA-MoS2 conjugates for cancer theranosis.

A novel optical thermometry based on the energy transfer from charge transfer band to Eu3+-Dy3+ ions

Optical thermometry based on the up-conversion intensity ratio of thermally coupled levels of rare earth ions has been widely studied to achieve an inaccessible temperature measurement in submicron scale. In this work, a novel optical temperature sensing strategy based on the energy transfer from charge transfer bands of W-O and Eu-O to Eu3+-Dy3+ ions is proposed. A series of Eu3+/Dy3+ co-doped SrWO4 is synthesized by the conventional high-temperature solid-state method. It is found that the emission spectra, emission intensity ratio of Dy3+ (572 nm) and Eu3+ (615 nm), fluorescence color, lifetime decay curves of Dy3+ (572 nm) and Eu3+ (615 nm), and relative and absolute sensitivities of Eu3+/Dy3+ co-doped SrWO4 are temperature dependent under the 266 nm excitation in the temperature range from 11 K to 529 K. The emission intensity ratio of Dy3+ (572 nm) and Eu3+ (615 nm) ions exhibits exponentially relation to the temperature due to the different energy transfer from the charge transfer bands of W-O and Eu-O to Dy3+ and Eu3+ ions. In this host, the maximum relative sensitivity Sr can be reached at 1.71% K−1, being higher than those previously reported material. It opens a new route to obtain optical thermometry with high sensitivity through using down-conversion fluorescence under ultraviolet excitation.

A multifunctional probe for ICP-MS determination and multimodal imaging of cancer cells

Inductively coupled plasma-mass spectrometry (ICP-MS) based bioassay and multimodal imaging have attracted increasing attention in the current development of cancer research and theranostics. Herein, a sensitive, simple, timesaving, and reliable immunoassay for cancer cells counting and dual-modal imaging was proposed by using ICP-MS detection and down-conversion fluorescence (FL)/upconversion luminescence (UCL) with the aid of a multifunctional probe for the first time. The probe consisted of a recognition unit of goat anti-mouse IgG to label the anti-EpCAM antibody attached cells, a fluorescent dye (Cy3) moiety for FL imaging as well as upconversion nanoparticles (UCNPs) tag for both ICP-MS quantification and UCL imaging of cancer cells. Under the optimized conditions, an excellent linearity and sensitivity were achieved owing to the signal amplification effect of nanoparticles and low spectral interference. Accordingly, a limit of detection (3σ) of 1×102 HepG2 cells and a relative standard deviation of 7.1% for seven replicate determinations of 1×103 HepG2 cells were obtained. This work proposed a method to employ UCNPs with highly integrated functionalities enabling us not only to count but also to see the cancer cells, opening a promising avenue for biological research and clinical theranostics.

Upconversion nanoparticles for bioimaging

AbstractFluorescent labeling is a widely used indispensable tool in biology. Conventional downconversion fluorescence labels with ultraviolet or short-wavelength excitation suffer from autofluorescence, low signal-to-noise ratio, and incident photo damage to living organisms. However, upconverting fluorescent nanoparticles emit detectable photons of higher energy in the near-infrared (NIR) or visible range upon irradiation with a NIR light in a process termed upconversion. They overcome some of the disadvantages faced by conventional downconversion labels with the advantages including very low autofluorescence, absence of photo damage to living organisms, high detection sensitivity, and high depth of light penetration, thus making them an ideal fluorescent label for bioimaging. The present review focuses on the features of upconversion nanoparticles, the applications of upconversion nanoparticles in bioimaging, and the bioimaging equipments and methods and discusses the obstacles and development trend of upconversion nanoparticles in bioimaging; we hope this work will provide insights into the study of relevant fields. Upconversion nanoparticles have special photoluminescent properties. Substantial advancements have been made in the field of upconversion nanoparticles for bioimaging. A large number of modifications of upconversion nanoparticles are studied to make them more hydrophilic and biocompatible. At the same time, the safety and toxicity of nanoparticles have caused wide public concern.

Microencapsulation of n-dodecane into zirconia shell doped with rare earth: Design and synthesis of bifunctional microcapsules for photoluminescence enhancement and thermal energy storage

We have designed a new type of bifunctional microcapsules composed of an n-dodecane PCM (phase change material) core and a rare-earth-doped zirconia shell for photoluminescence enhancement and thermal energy storage and have synthesized a series of microcapsule samples through in-situ polycondensation in a non-aqueous emulsion templating system. The scanning electron microscopic investigation indicated that the resultant microcapsules presented the regular spheres with a smooth surface and a uniform size distribution, while the transmission electron microscopy showed a well-defined core–shell structure for these microcapsules. The Fourier–transform infrared spectroscopy characterized the chemical compositions of the resultant microcapsules, and the rare-earth elements doped within the zirconia shell were confirmed by energy-dispersive X-ray patterns and X–ray photoelectron spectroscopy. The resultant microcapsules exhibited a good thermal regulation capability with high encapsulation and energy-storage efficiencies. Most of all, the photoluminescence characterization indicated that these rare-earth-doped microcapsules achieved a significant enhancement in emission intensity of the cyan-colored up-conversion and purple-colored down-conversion fluorescence after excited by radiation at wavelengths of 850 and 280 nm, respectively. The enhancement level of emission intensity varied with different rare-earth species and was determined by the bond length of rare-earth ion to oxygen in the solid solution of zirconia host.

Synthesis and down-conversion luminescence properties of Er3+/Yb3+ co-doped AlF3–PbF2–CaF2 powders

Er3+/Yb3+ co-doped oxy-fluoride powders with varying Er/Yb concentration were prepared by a melt quenching method at various sintering temperature. The effect of the Er/Yb doped concentration and sintering temperature were analyzed by using optical absorption and emission techniques. The Judd–Ofelt theory has been used to evaluate the three intensity parameters (Ωλ, where λ=2, 4 and 6) and calculate the oscillator strengths (fc). Ultraviolet-to-visible emissions were observed under the excitation of a 325nm CW laser. It was found that the down-conversion fluorescence intensity changes with the sintering temperature and Er/Yb content ratio, the results were explained with the level transitions in Er3+/Yb3+ co-doped systems. The intensity ratios (intensity of 437nm as reference) of the luminescence spectra that the samples sintered at various temperature are relevant to Ω6 parameter which indicates the vibration amplitude of the Er–O distance. The sintering temperature also has an influence on the intensity ratios via affecting the thermalization of the excited 4I15/2 level.

Enhancement and regulation of fluorescence emission from NaYF4:Yb3+, Er3+ nanocrystals by codoping Mn2+ ions.

NaYF4:Yb3+, Er3+, Mn2+ nanocrystals with cubic crystal phase were obtained by a facile solvothermal method through doping a proper amount of Mn2+ ions to the nanocrystals. The results of XRD and TEM showed that the as-prepared samples were well crystallized and their average size was about 25 nm. Under excitations at 978.5 nm and at 532 nm, obvious enhancement and regulation of upconversion and downconversion fluorescence were obtained. Upconversion emission spectra indicate that these effects were independent of doped concentrations of Er3+ and Yb3+, excitation power, and the excitation wavelength in the current study. It is concluded that the enhancement of fluorescence emissions is mainly due to the change of local symmetry around Er3+ ions, while the regulation of red-to-green ratios was caused by efficient energy transfer between Er3+ and Mn2+ ions. This kind of upconversion material has a great potential in bioimaging and drug delivery since the excitation and emission falls into the region of "optical window" of biological tissues.

Recent Advance of Biological Molecular Imaging Based on Lanthanide-Doped Upconversion-Luminescent Nanomaterials.

Lanthanide-doped upconversion-luminescent nanoparticles (UCNPs), which can be excited by near-infrared (NIR) laser irradiation to emit multiplex light, have been proven to be very useful for in vitro and in vivo molecular imaging studies. In comparison with the conventionally used down-conversion fluorescence imaging strategies, the NIR light excited luminescence of UCNPs displays high photostability, low cytotoxicity, little background auto-fluorescence, which allows for deep tissue penetration, making them attractive as contrast agents for biomedical imaging applications. In this review, we will mainly focus on the latest development of a new type of lanthanide-doped UCNP material and its main applications for in vitro and in vivo molecular imaging and we will also discuss the challenges and future perspectives.

Simultaneously enhancing up-conversion fluorescence and red-shifting down-conversion luminescence of carbon dots by a simple hydrothermal process.

Fluorescent carbon dots (CDs) have attracted great attention in the biomedical field owing to their remarkable fluorescence property, low toxicity, and excellent water solubility. Because of the "water window" effect, the CDs with upconversion fluorescence or longer wavelength downconversion fluorescence are particularly more suitable for bioimaging because they can weaken the auto-fluorescence interferences and penetrate the cell or tissue more deeply. In this study, we reported a facile method to simultaneously enhance the upconversion fluorescence and tune the downconversion luminescence of CDs from blue to green light by simply adding H2O2 in a hydrothermal process. The H2O2-treated green fluorescent CDs with excellent upconversion property showed a high yield of 34% and a quantum yield of 16.5%, and low cell cytotoxicity, which could be directly used for live Hela cell imaging.

SiO2@YBO3:Eu3+ Hollow Mesoporous Spheres for Drug Delivery Vehicle

A novel bifunctional (fluorescent, mesoporous) hollow sphere was prepared by coating luminescent YBO3:Eu(3+) nanoparticles onto uniform hollow mesoporous silica spheres (HMSs), derived from an etching strategy using spherical Fe3O4 as templates. The composites exhibit typical mesoporous shells, large interior space, high surface area, and well dispersed nanospheres with controlled size. In addition, the textural properties including the specific surface and pore volume can be easily altered by simply tuning of the spherical Fe3O4 cores. Upon ultraviolet (UV) excitation, the composite shows the characteristic (5)D0-(7)F1-4 red emission lines of Eu(3+) even after loading of the model drug. The composite with a large surface area and cavity was used as the host for loading the anticancer drug doxorubicin hydrochloride (DOX). It is observed that the multifunctional composites exhibit an obvious sustained release property and released in texture- and pH-sensitive patterns. Particularly, the down-conversion (DC) fluorescence intensity of the bifunctional vehicle increases with the release of drug molecules, making it possible to track the position and the drug release amount of the drug carrier system and to detect them by the change of fluorescence intensity.

Investigation of upconversion and downconversion fluorescence emissions from β-NaLn1F4:Yb3+, Ln23+ (Ln1 = Y, Lu; Ln2 = Er, Ho, Tm, Eu) hexagonal disk system

Uniform hexagonal β-NaLn1F4:Yb3+, Ln23+ (Ln1=Y, Lu; Ln2=Er, Ho, Tm, Eu) disks were synthesized with hydrothermal method in which the sodium citrate was used as a shape modifier. The experimental observation indicated that both upconversion and downconversion fluorescence emissions were significantly stronger in β-NaLuF4 than that for β-NaYF4. It was found that the stronger hypersensitive transitions were mainly due to the increase of J–O parameter (Ω2) in β-NaLuF4 host, while the stronger insensitive transitions were mainly caused by the stronger overlap of electron cloud that was induced by the decrease of LnF bond lengths. Additionally, the larger absorption strength in the near-infrared region is another important factor for the stronger fluorescence emissions. The current research has a great potential in improving near-infrared conversion efficiency of silicon solar cells.

Down-/up-conversion luminescence nanocomposites for dual-modal cell imaging.

Dual-modal luminescence nanocomposites (NCs) were successfully prepared via a facile and versatile strategy by embedding the hydrophobic down-conversion (DC) fluorescence ZnS:Mn2+ quantum dots (QDs) and up-conversion (UC) luminescence NaYF4:Er3+/Yb3+ nanoparticles (NPs) into hydrophilic polymer matrixes through in situ cross-linking polymerization. Due to the enriched carboxylic groups in the polymer matrixes, the as-prepared NCs are highly water-stable and bioconjugatable with chemical and biological moieties. The results of cytotoxicity assay and dual-modal luminescence cell imaging application of DC-UC NCs indicate that the as-prepared NCs are biocompatible and applicable in biomedical fields. The current work paves the way to the fabrication of multifunctional NCs including down- and up-conversion dual-modal luminescence, luminescence-magnetism, magnetic targeted drug vehicles and magnetic recyclable catalyst NCs, and will attract wide attention from the fields of chemistry, materials, catalysis, nanotechnology, nanobiotechnology and nanomedicine.

Upconversion nanoparticles and their composite nanostructures for biomedical imaging and cancer therapy

Upconversion nanoparticles (UCNPs), particularly lanthanide-doped nanocrystals, which emit high energy photons under excitation by the near-infrared (NIR) light, have found potential applications in many different fields, including biomedicine. Compared with traditional down-conversion fluorescence imaging, the NIR light excited upconversion luminescence (UCL) imaging relying on UCNPs exhibits improved tissue penetration depth, higher photochemical stability, and is free of auto-fluorescence background, which promises biomedical imaging with high sensitivity. On the other hand, the unique upconversion process of UCNPs may be utilized to activate photosensitive therapeutic agents for applications in cancer treatment. Moreover, the integration of UCNPs with other functional nanostructures could result in the obtained nanocomposites having highly enriched functionalities, useful in imaging-guided cancer therapies. This review article will focus on the biomedical imaging and cancer therapy applications of UCNPs and their nanocomposites, and discuss recent advances and future prospects in this emerging field.

Sub-10 nm BaYF5:Yb3+,Er3+ core–shell nanoparticles with intense 1.53 μm fluorescence for polymer-based waveguide amplifiers

Sub-10 nm BaYF5:Yb3+,Er3+ core–shell nanoparticles (NPs) were synthesized by a high boiling solvent process. Under a 980 nm laser excitation, up- and down-conversion fluorescence spectra from BaYF5:Yb3+,Er3+ NPs were recorded and analyzed. After coating the active-shell (containing Yb3+ ions) around the BaYF5:Yb3+,Er3+ NPs, the intensity of the 1.53 μm fluorescent band was enhanced by 11 times owing to surface passivation effect and efficient energy transfer between Yb3+ ions in active-shell and Er3+ ions. Furthermore, the NPs showed excellent redispersibility in common nonpolar solvents. By dispersing BaYF5:Yb3+,Er3+ active-core–active-shell NPs into an SU-8 2005 polymer, we constructed polymer-based optical waveguide amplifiers and measured their performance. For an input signal power of 0.1 mW and a pump power of 200 mW, a relative optical gain of ∼6.3 dB was obtained at 1535 nm in a 13 mm-long waveguide.

Polymer encapsulated upconversion nanoparticle/iron oxide nanocomposites for multimodal imaging and magnetic targeted drug delivery

Multimodal imaging and imaging-guided therapies have become a new trend in the current development of cancer theranostics. In this work, we encapsulate hydrophobic upconversion nanoparticles (UCNPs) together with iron oxide nanoparticles (IONPs) by using an amphiphilic block copolymer, poly (styrene-block-allyl alcohol) (PS 16- b-PAA 10), via a microemulsion method, obtaining an UC-IO@Polymer multi-functional nanocomposite system. Fluorescent dye and anti-cancer drug molecules can be further loaded inside the UC-IO@Polymer nanocomposite for additional functionalities. Utilizing the Squaraine (SQ) dye loaded nanocomposite (UC-IO@Polymer-SQ), triple-modal upconversion luminescence (UCL)/down-conversion fluorescence (FL)/magnetic resonance (MR) imaging is demonstrated in vitro and in vivo, and also applied for in vivo cancer cell tracking in mice. On the other hand, a chemotherapy drug, doxorubicin, is also loaded into the nanocomposite, forming an UC-IO@Polymer-DOX complex, which enables novel imaging-guided and magnetic targeted drug delivery. Our work provides a method to fabricate a nanocomposite system with highly integrated functionalities for multimodal biomedical imaging and cancer therapy.

Preparation and Photoluminescence Properties of Nd<sup> 3+</sup> -Doped Silicate Glasses

The glass samples of SiO2-Al2O3-CdO-Li2O-K2O-Na2O with different Nd3+-doped concentration by high - temperature solid-state reaction method were fabricated and the absorption spectrums as well as down-conversion fluorescence spectrums were tested. The experiments confirmed that a strong fluorescence emission at the wavelength of 1064 nm were obtained with pumped wavelength of 514 nm, 532 nm and 808 nm respectively in Nd3+ -doped cadmium silicate glasses.

Small Upconverting Fluorescent Nanoparticles for Biomedical Applications

Fluorescent labels have been widely used for biological applications, primarily in imaging and assays. Traditional fluorophores such as fluorescent dyes are mainly based on downconversion fluorescence, which have several drawbacks such as photobleaching, high background noise from autofluorescence, and considerable photodamage to biological materials. Upconverting fluorescent nanoparticles emit detectable photons of higher energy in the near-infrared (NIR) or visible range upon irradiation with an NIR light in a process termed 'upconversion.' They overcome some of the disadvantages faced by conventional downconversion labels, thus making them an ideal fluorescent label for biological applications. This review looks at the development of these particles, critically examines the reported applications, and discusses their future in biomedicine.

Solvent-assisted selective synthesis of NaLaF 4 and LaF 3 fluorescent nanocrystals via a facile solvothermal approach

A facile solvothermal approach was developed to selectively synthesize water-soluble NaLaF 4 or LaF 3 nanocrystals (NCs) by tuning the solvent components. In ethonal/H 2O media, high-quality LaF 3 NCs were prepared by using NaF and LaCl 3 as the precursors. More interestingly, thermodynamically non-preferred NaLaF 4 nanorods could be obtained when ethylenediamide (EN) was introduced to the ethonal/H 2O solvent. All of the products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the crucial effects of EN on morphology and structure of the NCs were studied. Furthermore, by doping different lanthanide ions, these LaF 3 and NaLaF 4 NCs could emit intense upconversion (UC) or downconversion (DC) fluorescence, which showed potential applications in color displays, light-emitting diodes, optical storage and optoelectronics.

Up and down conversion fluorescence studies on combustion synthesized Yb 3+/Yb 2+: MO-Al 2O 3 (M=Ca, Sr and Ba) phosphors

The ytterbium ions doped MO-Al 2O 3 (M=Ca, Sr and Ba) phosphors have been synthesized through combustion technique and their up and down conversion fluorescence properties have been studied and compared. The samples were calcinated at different temperatures and their FTIR and XRD spectra have shown a close relationship. With 976 nm excitation all these phosphors show cooperative upconversion emission at 488 nm from the pairs of two Yb 3+ ions along with an unexpected broad upconversion band in the blue green region and has been assigned to arise from the defect centers. Contrary to this upconversion emission, calcium aluminate phosphor exhibits bright and very broad down-conversion fluorescence (FWHM≈160 nm) upon UV (266 nm) excitation due to Yb 2+ ions. The inter-conversion between the 3+ and 2+ valence states of Yb ion has been observed on calcinations of samples in open atmosphere and has been correlated to the emission properties. The Yb 2+ ions containing calcium aluminate phosphor has been found suitable for producing broad band light in the visible region (white light). Lifetime of the emitting states of Yb 3+ and Yb 2+ ions have also been measured and discussed.