Upconversion Nanophosphors Research Articles

Biocompatible Yb3+/Er3+ Co-activated La2(WO4)3 Upconversion Nanophosphors for Optical Thermometry, Biofluorescent, and Anticancer Agents.

Non-cytotoxic upconversion nanocrystals are preferred candidates because they offer exceptional advantages for numerous applications, ranging from optical thermometry to bioimaging/biomedical applications. In this report, we demonstrate the luminescence characteristics and practical utility of a multifunctional upconversion nanophosphor based on Yb3+/Er3+:La2(WO4)3 (LWO) flakes. Strong upconversion green emission was observed from 6-mol % Er3+-doped LWO nanophosphor flakes excited by a 980 nm laser. We further enhanced the upconversion emission considerably by co-doping LWO nanophosphors with Yb3+/Er3+ to exploit energy migration from Yb3+ to Er3+ ions. The exceptional improvement in upconversion green and near-infrared emission was achieved by Yb3+ ion co-doping up to 6 mol %; beyond 6 mol %, emission intensities remarkably dropped due to concentration quenching. Photometric parameters were evaluated with and without Yb3+ ion-doped LWO nanophosphors, which exhibited a high green color purity of 95.6%, to elucidate their energy transfer mechanism. In addition, temperature-dependent upconversion emission trends were evaluated by analyzing the fluorescence intensity ratio, exhibiting higher temperature sensitivity than that previously reported. This suggests the applicability of our proposed nanophosphors to optical thermometry. As for bioimaging applications, the non-cytotoxicity of the optimized nanophosphor was confirmed based on distinct fluorescence images of a normal fibroblast cell line (L929). Furthermore, we demonstrated the strong cytotoxicity of nanophosphors against human colon cancer (HCT-116) cells. Based on the results, non-cytotoxic Yb3+(6 mol %)/Er3+ (6 mol %):LWO upconversion nanophosphor flakes are expected to be exceptional candidates owing to their extensive suitability to the fields of upconversion lasers, optical thermometry, and biomedical and anticancer applications. The results indicate the potential of upconversion materials in the effective execution of multiple strategic applications.

High-Gravity-Assisted Intensified Preparation of Er-Doped and Yb/Er-Codoped CaF2 Upconversion Nanophosphors for Noncontact Temperature Measurement

High-Gravity-Assisted Intensified Preparation of Er-Doped and Yb/Er-Codoped CaF₂ Upconversion Nanophosphors for Noncontact Temperature Measurement

Paper-supported near-infrared-light-triggered photoelectrochemical platform for monitoring Escherichia coli O157:H7 based on silver nanoparticles-sensitized-upconversion nanophosphors

Escherichia coli O157:H7 (E. coli O157:H7) is a typical foodborne pathogen that contaminates food and water, leading to lots of infectious diseases. In this study, a near-infrared-responsive photoelectrochemical (PEC) sensing platform for the ultrasensitive detection of E. coli O157:H7 was established by assembling a flexible conductive paper electrode with core-shell-structured upconversion nanophosphors (UCNPs) @SiO2@Ag and carbon self-doped graphitic carbon nitride (C-g-C3N4). In this design, UCNPs act as a self-powered that change near infrared (NIR) excitation into visible emission, while the semiconductor material C-g-C3N4 acts as the energy-conversion center to convert visible illumination to photocurrent. Importantly, silver nanoparticles (AgNPs) significantly enhance the upconversion luminescence of UCNPs and facilitate the separation and transportation of photoelectrons by the localized surface plasmon resonance effect. Using the antimicrobial peptide Magainin I as the recognition element, E. coli O157:H7 was specifically captured and determined directly for its steric hindrance effect on the photoelectrode. As a result, the photocurrent decreased linearly with the increase in E. coli O157:H7 in a wide range from 5 to 5 × 106 colony-forming units per mL (CFU/mL), and the detection limit was as low as 2 CFU/mL. Finally, the proposed NIR PEC sensor was successfully utilized for the determination of E. coli O157:H7 in contaminated pork, cabbage, and milk samples without enrichment of the bacteria in 50 min.

Spectral Engineering and Morphological Tuning of Amino Acid Capped Hydrophilic Upconversion Nanophosphors

Upconversion, the process of generating a higher-energy photon from lower-energy photons, has captivated research interest over the years due to its unique applications in the field of biological i...

Ultra-Sensitive water detection based on NaErF4@NaYF4 high-level-doping upconversion nanoparticles

Water-sensitive detection plays a vital role in our society and life, such as the chemical industry, environmental monitoring, and food inspection. In this work water sensitivity as high as 5 ppm (0.0005 vol%) is realized based on a novel upconversion nanophosphor. Different from the popularly employed low-doping strategies, an efficient high-level-doping nanostructure, i.e., NaErF4@NaYF4, is tailored for the desired upconversion emission, resulting in more than one order of magnitude enhancement of the sensitivity compared to the record of the low-doped counterparts. The superiority of this structure is determined to come from the robust interactions between the Er3+ ions and the water molecules adsorbed on the particle surface. This design offers a new strategy of nanophosphor structures for ultrasensitive water sensing and sheds light on further optimization of nanophosphor based sensors.

Rare-Earth Doped Upconverting Nanophosphors for Light-Mediated Biocidal Surface Development

Since the earliest civilization, diminishing the occurrence and subsequent transmission of pathogenic microorganisms in the indoor environment has been one of the utmost priorities to the human society. In line with intensive research towards the surface disinfection through the use of several photocatalytic processes, rare-earth doped upconverting nanophosphors (UCNPs) have recently drawn a great attention on the basis of their purely optical phenomenon of directly converting visible light into germicidal ultraviolet radiation (namely ultraviolet C) via the unique photoluminescence process namely ‘upconversion’. The efficient upconversion of abundant visible light into ultraviolet photons in the germicidal range and, consequently, effective biocidal action while coated onto surfaces enable UCNPs as a potential candidate to be used for inhibiting germ spreading through the inanimate surface in public places, hospitals and so forth.

Orthogonal R/G/B Upconversion Luminescence-based Full-Color Tunable Upconversion Nanophosphors for Transparent Displays.

Here, excitation orthogonalized red/green/blue upconversion luminescence (UCL)-based full-color tunable rare-earth (RE) ion-doped upconversion nanophosphors (UCNPs) are reported. The LiREF4-based core/sextuple-shell (C/6S) UCNPs are synthesized, and they consist of a blue-emitting core, green-emitting inner shell, and red-emitting outer shell, with inert intermediate and outermost shells. The synthesized C/6S UCNPs emit blue, green, and red light under 980, 800, and 1532 nm, respectively. Importantly, by combining incident near-infrared (NIR) light with various wavelengths (800, 980, and 1532 nm), full-color UCL including blue, cyan, green, yellow, orange, red, purple, and white UCL is achieved from the single C/6S UCNP composition. The color gamut obtained from the C/6S UCNPs shows 101.6% of the sRGB standard color gamut. Furthermore, transparent C/6S UCNP-polydimethylsiloxane (PDMS) composite is prepared. Full-color display realized in the transparent C/6S UCNP-PDMS composite indicates the feasibility of constructing the C/6S UCNP-based three-dimensional volumetric displays with wide color gamut.

Competitive near-infrared PEC immunosorbent assay for monitoring okadaic acid based on a disposable flower-like WO3-Modified screen-printed electrode

The long-term toxic effects of okadaic acid (OA) in shellfish pose a serious threat to public health, negatively impacting the development of the shellfish aquaculture industry. In this study, a novel competitive near-infrared-mediated photoelectrochemical immunosorbent assay (cNIR-PECIA) was developed for ultrasensitive and highly selective detection of OA based on NaYF4:Yb, Tm upconversion nanophosphors (UCNPs) and a flower-like WO3-modified screen-printed electrode (FL-WO3 SPE). The UCNPs function as a self-powder to convert NIR excitation into visible emissions. FL-WO3 fully utilizes the visible illumination and induces the separation of electron–hole pairs, thus generating a photocurrent. After conjugating monoclonal antibodies against OA on UCNPs (UCNPs-Ab), the bright PEC immunoprobe selectively captured OA molecules, which were then determined by a competitive indirect immunosorbent assay. Under optimal conditions, the 50% inhibitory concentration of the immunosensor was 0.09 ng mL−1. The OA concentration had a linear relationship with the antibody binding rate in the range of 0.01–60 ng mL−1 with an extremely low detection limit of 0.007 ng mL−1. Finally, the proposed cNIR-PECIA was successfully utilized to analyze OA content in mussel samples. This study affords new ideas for constructing NIR PEC sensors by using upconversion luminescent materials to match semiconductors. The superior sensing properties indicate their potential applicability in food safety analysis.

Синтез и характеризация наноразмерных апконвертирующих фосфоров NaYF4:Yb3+:Er3+/NaYF4

We carried out the solvothermal synthesis of UCNPs with the core/shell structure NaYF4:Yb3+:Er3+/NaYF4 and analyzed their photoluminescent properties depending on the nanoparticle size and preparative synthesis conditions. It has been shown that intensity and lifetime of the photoluminescence of the upconversion nanophosphors depend on the intensity of laser excitation, size of the nanoparticles and presence of an inert shell. Upon the formation of an inert shell on the surface of NaYF4:Yb3+:Er3+ nanoparticles the conversion efficiency of visible and NIR radiation in different spectral regions can increase by more than an order of magnitude due to shielding of luminescent centers from nonradiative losses at surface defects.

Anticounterfeiting and Security Applications of Rare-Earth Upconversion Nanophosphors

Anticounterfeiting and Security Applications of Rare-Earth Upconversion Nanophosphors

Positive role of the long luminescence lifetime of upconversion nanophosphors on resonant surfaces for ultra-compact filter-free bio-assays.

We introduce a compact array fluorescence sensor principle that takes advantage of the long luminescence lifetimes of upconversion nanoparticles (UCNPs) to deploy a filter-free, optics-less contact geometry, advantageous for modern biochemical assays of biomolecules, pollutants or cells. Based on technologically mature CMOS chips for ∼10 kHz technical/scientific imaging, we propose a contact geometry between assayed molecules or cells and a CMOS chip that makes use of only a faceplate or direct contact, employing time-window management to reject the 975 nm excitation light of highly efficient UCNPs. The chip surface is intended to implement, in future devices, a resonant waveguide grating (RWG) to enhance excitation efficiency, aiming at the improvement of upconversion luminescence emission intensity of UCNP deposited atop of such an RWG structure. Based on mock-up experiments that assess the actual chip rejection performance, we bracket the photometric figures of merit of such a promising chip principle and predict a limit of detection around 10-100 nanoparticles.

Bright Blue, Green, and Red Luminescence from Dye-Sensitized Core@Shell Upconversion Nanophosphors under 800 nm Near-Infrared Light.

In this study, Li-based blue- and green-emitting core@shell (C@S) upconversion nanophosphors (UCNPs) and NaGdF4-based red-emitting C@S UCNPs were synthesized, and IR-808 dyes were conjugated with the C@S UCNPs to enhance upconversion (UC) luminescence. The surface of the as-synthesized C@S UCNPs, which was originally capped with oleic acid, was modified with BF4− to conjugate the IR-808 dye having a carboxyl functional group to the surface of the UCNPs. After the conjugation with IR-808 dyes, absorbance of the UCNPs was significantly increased. As a result, dye-sensitized blue (B)-, green (G)-, and red (R)-emitting UCNPs exhibited 87-fold, 10.8-fold, and 110-fold enhanced UC luminescence compared with B-, G-, and R-emitting Nd3+-doped C@S UCNPs under 800 nm near-infrared (NIR) light excitation, respectively. Consequently, dye-sensitized UCNPs exhibiting strong UC luminescence under 800 nm NIR light excitation have high applicability in a variety of biological applications.

Cyanine-modified near-infrared upconversion nanoprobe for ratiometric sensing of N2H4 in living cells

Although being as an important chemical material in industry, hydrazine (N2H4) is highly toxic to the humans and animals. The development of sensitive methods for the detection of hydrazine is meaningful. Herein, we develop a new organic-inorganic hybrid nanoprobe for the detection of N2H4 based on luminescent resonance energy transfer (LRET) process. The nanoprobe contains N2H4-responsive NIR cyanine dye (CQM1) and α-cyclodextrin (CD) anchored on the surface of lanthanide-doped upconversion nanophosphors (UCNPs). In the presence of hydrazine, the hybrid materials (CQM1-UCNPs) showed the a large ratiometric luminescent signal change with high sensitivity and selectivity. More importantly, by taking advantage of ratiometric Upconversion luminescent (UCL) signal and the features of NIR emission/excitation, the nanoprobe was successfully applied for visualization of hydrazine in living cells for the first time.

Aptamer-Functionalized Upconverting Nanoformulations for Light-Switching Cancer-Specific Recognition and In Situ Photodynamic-Chemo Sequential Theranostics.

Biomarker-activatable theranostic formulations offer the potential for removing specific tumors with a high diagnostic accuracy and a significant pharmacological effect. Herein, we developed a novel activatable theranostic nanoformulation UAS-PD [upconversion nanophosphor (UCNP)-aptamer/ssDNA-pyropheophorbide-a (PPA)-doxyrubicin (DOX)], which can recognize specific cancer cells with sensitivity and trigger the localized photodynamic destruction and enhanced chemotherapy. UAS-PD was constructed by the conjugation of UCNPs and aptamer probes containing the photosensitizer PPA and the chemotherapeutic drug DOX. When cancer cells are present, the UAS-PD specifically binds to PTK7, an overexpressed protein present on the surface of cancer cells, through conformational recombination of the aptamer structure and switches its upconversion luminescence from 655 to 540 nm. This long-lived ratiometric optical signal provides an ultrasensitive detection limit as low as 3.9 nM for PTK7. Changes in the conformation of UAS-PD can also induce PPA to approach UCNPs, which can produce cytotoxic singlet oxygens under near-infrared excitation to destroy the cell membrane and enhance its permeability for the simultaneously released DOX that targets cellular DNA degradation, which results in a highly effective tumor-killing effect by synergistic extra-intracellular sequential damage.

Synthesis of Yb3+/Ho3+ co-doped Y2O3 nanoparticles and its application to dye sensitized solar cells

In this study, a series of Yb3+/Ho3+ co-doped Y2O3 up-conversion (UC) nanophosphors was fabricated by a homogeneous precipitation method. The photoluminescence emission in the visible regions of the nanophosphors has been investigated under 980 nm IR laser excitation. The nanophosphors exhibited strong visible green and weaker red up-conversion emissions. The effects of various concentrations of Yb3+ (1–4 mol%) on the photoluminescence properties of fabricated nanophosphors was also investigated. The fabricated UC nanophosphors were incorporated in the DSSC and their influence on the photovoltaic performance of the DSSC was characterized by a current-voltage curve, and incident photon to current conversion efficiency. Compared with the DSSC without the UC nanoparticles which had a cell efficiency of 4.27%, the DSSC incorporating Y2O3:Ho3+/ Yb3+ UC nanoparticles showed an enhanced cell efficiency of 4.79%.

Green route synthesized upconverting (NaYF4: Yb3+, Tm3+)nanophosphors and its photophysical and magnetic Properties

Here we describe a green synthetic route for the development of paramagnetic, upconverting nanophosphors (UPCN_M) with enhanced luminescence using M.oleifera leaf extract. The current work demonstrates the influence of leaf extracton α→β phase transformation, size, morphology, magnetic behavior, and photothermal heat generation by upconverting nanophosphor under NIR illumination (wavelength~975 nm). The green route assisted upconverting nanophosphors synthesized in 2h, displayed better emission intensity as compared to nanophosphors prepared in15h, chemically, using EDTA (UPCN_EDTA).Further its (UCPN_M) suspension in DI water displayed photothermal heating rate, as high as 1.15 °C/min (ΔT= 11.5°C,Tmax= 40 °C) without incorporation of external NIR absorbing entity, physiologically relevant enough to carry out photothermal studies on biological subjects. At 2K and higher applied magentic field, the UPCN_M displayed super-paramagnetic behaviour with saturation magnetic moment as high as ~10.5 emu/g, although at room temprature (27 °C) intrinsically behaved as a paramagnetic magnet.

Nanosized Anti-Stokes Phosphors for Antitumor Drug Delivery and Solid Tumor Theranostics.

Abstract-Theranostics is the direction in modern biomedicine aimed at developing drugs that combine the capabilities of diagnosis and therapy of tumors in one agent. Upconversion nanophosphors (UCNPs) are inorganic crystalline materials that can be used to create a nanoplatform providing diagnostic and therapeutic modalities. They have been proposed as luminescent markers for optical imaging of biological tissue due to their anti-Stokes luminescence, lack of photodegradation and low toxicity. In this article, UCNPs as a theranostic agent for both optical imaging and delivery of anticancer drugs have been offered. To obtain biocompatible nanocomplexes, UCNP surface with a core/shell structure of NaYF4:Yb3+Tm3+/NaYF4 was modified with polylactic acid in the presence of various stabilizers (dextran, polyvinyl alcohol, and poly-N-vinylpyrrolidone). To give the therapeutic modality to the nanocomplex, the antitumor antibiotic doxorubicin was loaded into the polymer shell. The loading efficiency was up to 0.1 mg per 1 mg UCNPs. The toxicity and the intracellular accumulation of nanocomplexes were evaluated in vitro. It was concluded that the modification of UCNPs with polylactic acid provides the transport of doxorubicin, allowing the combination of diagnostic and therapeutic modalities in one agent.

Controllable Synthesis of Upconversion Nanophosphors toward Scale‐Up Productions

AbstractUpconversion nanophosphors (UCNPs) are considered as an important synthesis arm within biomedical and energy sectors due to their unique optical characteristics, which can convert near‐infrared light into higher energy emissions. However, key challenges, cost, compatibility of the materials, etc. have to be taken into serious consideration to transform this in‐lab UCNPs technology into scale‐up production for wider commercial needs. This review highlights the fundamental concepts of synthetic approaches for UCNPs and recaps recent advances in terms of large‐scale production. A number of typical synthesis routes in both batch and continuous processes are reviewed, alongside their limitations and potential improvements when being considered for mass production. By discussing and exploiting the technical compacity for the potential synthetic trends, key challenges, and expectations of future synthesis methods for UCNPs are also outlined.

Simultaneous improvement in emission intensity and spectral purity of red photon upconversion in Gd2O3:Yb3+/Er3+ phosphors under 1550 nm excitation

Upconversion luminescent nano-materials with both excitation and emission peaks in the “optical window” is of significant importance for application in deeper bio-imaging, due to the weak effects of light absorption, light scattering, and auto-fluorescence. This paper reports an Er3+ self-sensitized red up-converting nanophosphors with improved emission intensity and spectral purity. The influence of Yb3+ concentration on upconversion luminescence properties is investigated comprehensively. Compared with the sample without Yb3+ doping, the luminescence intensity in the sample with 10% Yb3+ is increased by 12.9 times. Moreover, the dominant wavelength at 1550 nm excitation is about 60 nm larger than that excited at 980 nm. It has been demonstrated that Yb3+ co-doping can not only improve the photon absorption at 1550 nm and the probability of red emission, but also suppress other light emissions and phonon emission through the selective population of red-emitting level.

Sub-20 nm LiErF4-Based Upconversion Nanophosphors for Simultaneous Imaging and Photothermal Therapeutics

This study reports red-emitting LiErF4:Tm-based upconversion nanophosphors (UCNPs) with small size and high brightness for simultaneous upconversion luminescence (UCL) imaging and photothermal ther...