Doped Upconversion Nanoparticles Research Articles

Energy transfer designing in lanthanide-doped upconversion nanoparticles.

Lanthanide (Ln3+)-doped upconversion nanoparticles (UCNPs), exhibiting excellent optical properties such as long photoluminescence lifetime, narrow emission bandwidth, and low autofluorescence background, have been applied in many fields, especially in biological analysis and medical diagnostics. Despite the exciting progress, the applications of Ln3+-doped UCNPs are hindered by the small absorption cross-section and low upconversion luminescence efficiency of Ln3+. To this regard, several effective strategies associated with energy transfer designing have been proposed to modulate the upconversion luminescence properties of Ln3+ in the past few decades. In this feature article, we focus on the most recent development of optical property designing in Ln3+-doped UCNPs on the basis of energy transfer between Ln3+-Ln3+, Ln3+-dyes, and Ln3+-quantum dots. Some future efforts towards the energy transfer designing in Ln3+-doped UCNPs are also proposed.

Correction: Video-rate upconversion display from optimized lanthanide ion doped upconversion nanoparticles.

Correction for 'Video-rate upconversion display from optimized lanthanide ion doped upconversion nanoparticles' by Laixu Gao et al., Nanoscale, 2020, DOI: .

Video-rate upconversion display from optimized lanthanide ion doped upconversion nanoparticles.

Volumetric displays that create bright image points within a transparent bulk are one of the most attractive technologies in everyday life. Lanthanide ion doped upconversion nanoparticles (UCNPs) are promising luminescent nanomaterials for background free, full-colour volumetric displays of transparent bulk materials. However, video-rate display using UCNPs has been limited by their low emission intensity. Herein, we developed a video-rate upconversion display system with much enhanced brightness. The integral emission intensity of the single UCNPs was fully employed for video-rate display. It was maximized by optimizing the emitter concentration and, more importantly, by temporally synchronizing the scanning time of the excitation light to the the raised emission time of the single UCNPs. The excitation power dependent emission response and emission time decay curves were systematically characterized for the single UCNPs with various emitter concentrations from 0.5% to 6%. 1%Tm3+ doped UCNPs presented the highest integral emission intensity. By embedding this UCNPs into a polyvinyl acetate (PVA) film, we achieved a two-dimensional (2D) upconversion display with a frame rate of 29 Hz for 35 by 50 pixels. This work demonstrates that the temporal response as well as the integral emission intensity enable video-rate upconversion display.

Two-Photon Excitation/Red Emission, Ratiometric Fluorescent Nanoprobe for Intracellular pH Imaging.

Herein, we describe a novel two-photon excitation/red emission-based ratiometric pH nanosensor consisting of a pH-sensitive two-photon dye and Tm3+-doped upconversion nanoparticles (UCNP). The fluorescence emission ratio between the dye (610 nm) and UCNPs (810 nm) (I610/I810) provides a linear indicator of pH values in the range from pH 4.0 to 6.5 with high sensitivity. These nanoprobes selectively accumulate in the lysosomes of cells, making them suitable for lysosomal pH tracking. This pH nanoprobe has been successfully applied in visualizing chemically stimulated changes of intracellular pH in living cells and tissues.

The 1G4 - 3H6 electron transition process of Tm3+ promoted by nonmetallic plasmon

The coupling of rare-earth ions doped upconversion nanoparticles (UCNPs) with localized surface plasmon resonance (LSPR) of noble metal has attracted more interest because of improving luminescent efficiency of UCNPs. The nonstoichiometric semiconductor tungsten oxides can provide a possibility for the achievement of effective upconversion luminescence enhancement owning to concentrating and transferring the NIR-plasmonic energy in upconversion system. In this work, Yb3+/Tm3+-doped NaYF4 nanoparticles (NaYF4:Yb-Tm NPs)/ W18O49 nanowires (NWs) composite film which can tremendously improve the upconversion luminescence of Tm3+ as high as 140-fold has been fabricated. Investigations show that the LSPR-induced plasmonic energy transfer process produced by W18O49 NWs is the primary reason for enhancing the upconversion luminescence of NaYF4:Yb-Tm NPs, originating from much more intense excitation electric-field to generate more electrons on the excited state energy-levels of Tm3+ ions. It is anticipated that the development of non-metallic plasmon-sensitized upconversion luminescence materials may provide a platform for widely exploring application in biomedical imaging, therapeutics, and energy conversion.

Ultrasensitive broadband photodetector using electrostatically conjugated MoS2-upconversion nanoparticle nanocomposite

Hybrid or composite nanomaterials have emerged that demonstrates superior optoelectronic performance over pure nanomaterials that lacks broadband usage, or responsivity, or both, mainly because of the limitation of the collection of photogenerated carriers. We have addressed this problem by using a composite of MoS2 and a multi-photon absorbing lanthanide doped upconversion nanoparticles (UCNPs), that emits in the visible, to make a photodetector (PD) device with ultrahigh broadband responsivity. Single flake MoS2 electrostatically conjugated with UCNPs were used to fabricate the PD device with platinum, and gold contacts. The device was irradiated with UV-to-NIR illumination, at different power density, to study its broadband photosensitivity. Photoresponsivities in excess of 100 A W-1 is easily obtained; a highest responsivity of 1254 A W-1 is reported for 980 nm at 1.0 V bias. An unprecedented normalized gain of 7.12 × 10−4 cm2 V−1, and Detectivity of 1.05 × 1015 Jones (@980 nm, 1 V) was obtained which is, to the best of our knowledge, the highest reported till date for this device class. Under vacuum conditions even higher values of these device parameters were obtained, while losing on the response speeds. The photoresponsivity in the nanocomposite followed the trend of the convoluted optical absorption of the individual components. Real application of the PD device was demonstrated using non-laser domestic appliances such as sodium vapour lamp, mobile phone flash light, and air-condition remote controller.

Generation of red-NIR bi-modal fluorescence in hybrid nanostructure

We have developed an ultrafine (<15 nm) hybrid nanoparticle (HNPs) consisting of lanthanide doped upconversion nanoparticles (UCNPs, NaY0.797Tm0.003Yb0.2F4), manganese doped zinc selenide quantum dots-(QDs, Mn:ZnSe) and silver nanoparticles (AgNPs). Synthesized HNPs involves electrostatic interaction among constituent particles. Thus, the coupling among constituent particles is relatively more strong contrary to the usual weak Van der Waals force based HNPs. HNPs emit nearly pure red-NIR emission both through normal fluorescence (under UV light excitation) and through photon upconversion process (under NIR excitation). AgNPs act as an optical filter for blue emission both for- (i) band to band transition of ZnSe and (ii) UC emission of Tm3+ ions (1G4→3H6) and thus turns the overall emission color to be in red-NIR region. Decay time measurement probes that, quenching of blue emission bands are primarily due to resonance energy transfer from UCNPs and QDs to the AgNPs (40 μL) with an energy transfer efficiency of 36% and 70%, respectively. These ultrafine and bimodal emitting HNPs could be suitable as optical imaging probe, in first biological window, and for other optoelectronic applications.

Recent Progress of Rare-Earth Doped Upconversion Nanoparticles: Synthesis, Optimization, and Applications.

Upconversion is a nonlinear optical phenomenon that involves the emission of high‐energy photons by sequential absorption of two or more low‐energy excitation photons. Due to their excellent physiochemical properties such as deep penetration depth, little damage to samples, and high chemical stability, upconversion nanoparticles (UCNPs) are extensively applied in bioimaging, biosensing, theranostic, and photochemical reactions. Here, recent achievements in the synthesis, optimization, and applications of UCNP‐based nanomaterials are reviewed. The state‐of‐the‐art approaches to synthesize UCNPs in the past few years are introduced first, followed by a summary of several strategies to optimize upconversion emissive properties and various applications of UCNPs. Lastly, the challenges and future perspectives of UCNPs are provided as a conclusion.

Control synthesis, subtle surface modification of rare-earth-doped upconversion nanoparticles and their applications in cancer diagnosis and treatment.

Rare earth doped upconversion nanoparticles (UCNPs) are a new class of luminescent materials that can absorb long-wavelength near-infrared photons and emit short-wavelength UV-visible photons. UCNPs have little damage to biological tissues, have deep tissue penetration ability, have no background fluorescence noise interference, have high imaging sensitivity, and have no photobleaching effect. In the field of biomedicine, especially in the field of diagnosis and treatment of cancer, a wide range of research interests has arisen. In this paper, we briefly introduce the luminescent principle of rare-earth doped UCNPs, discuss several widely used control synthesis and modification methods, and focus on the research progress of UCNPs in detection of cancer cells, photodynamic therapy (PDT) and photothermal therapy (PTT) field. We also summarize the application of UCNPs as a diagnostic and therapeutic integrated nanoplatform in the diagnosis and treatment of cancer. At last, we explore the application challenge and prospect of UCNPs in oncology field.

An aptasensor based on upconversion nanoparticles as LRET donors for the detection of exosomes

Exosomes may be used as a crucial medium for the early diagnosis and potential therapy of tumors because of containing a variety of biological information. Therefore, the accurate quantitative analysis of exosomes is especially important in the biomedical field. Herein, we proposed a washing-free aptasensor based on luminescence resonance energy transfer (LRET) between rare-earth doped upconversion nanoparticles (UCNPs) donor and tetramethyl rhodamine (TAMRA) acceptor for highly sensitive detection of exosomes. Therein, the combination of UCNPs and TAMRA can be achieved through the coupling of aptamers to the epithelial cell adhesion molecule (EpCAM), the highly expressed surface proteins of the exosomes. Therefore, when the system of UCNPs-TAMRA in the presence of exosomes is excited by near-infrared light at 980 nm, TAMRA emits yellow fluorescence at 585 nm due to LRET. As a result, the fluorescence intensity at 585 nm is linearly correlated to the concentration of exosomes, which is available for the detection and quantification of exosomes. Under optimal conditions, the proposed approach can reach a low limit of detection (LOD) of 80 particles/μL, and effectively reduce the background signal by using UCNPs as an energy donor. Moreover, this proposed aptasensor can be universally applied to the detection of other targets by strictly screening the aptamers.

Up-conversion fluorescence biosensor for sensitive detection of CA-125 tumor markers

Sensitive and specific bioassays of tumor markers are critical for early cancer detection and treatment. In recent years, lanthanide (Ln3+) doped upconversion nanoparticles (UCNPs) have attracted wide attentions in tumor markers detection. Herein, we combined NaYF4:Yb,Tm and silver nanoparticles, serving as energy donor and receptor, respectively, to form an up-conversion fluorescence based inhibitory tumor marker biosensor system. The tumor marker CA-125 molecules are labeled with silver NPs, and the energy transfer fluorescent signal can be detected between the UCNPs and the silver NP receptors. The biosensor shows good stability, high sensitivity and selectivity in the tumor marker concentration range from 5 to 100 ng/mL, as well as a detection limit of 120 pg/mL. Due to the advantage of ease of fabrication and operation, low cost and high information capacity, this technology holds great potential for the clinical applications.

Ultra-stable near-infrared Tm3+-doped upconversion nanoparticles for in vivo wide-field two-photon angiography with a low excitation intensity

Two-photon luminescence with near-infrared (NIR) excitation of upconversion nanoparticles (NPs) is of great importance in biological imaging due to deep penetration in high-scattering tissues, low auto-luminescence and good sectioning ability. Unfortunately, common two-photon luminescence is in visible band with an extremely high exciation power density, which limits its application. Here, we synthesized NaYF4:Yb[Formula: see text]Tm@NaYF4 upconversion NPs with strong two-photon NIR emission and a low excitation power density. Furthermore, NaYF4:Yb[Formula: see text]Tm@NaYF4@SiO2@OTMS@F127 NPs with high chemical stability were obtained by a modified multilayer coating method which was applied to upconversion NPs for the first time. In addition, it is shown that the as-prepared hydrophillic upconversion NPs have great biocompatibility and kept stable for 6 hours during in vivo whole-body imaging. The vessels with two-photon luminescence were clear even under an excitation power density as low as 25[Formula: see text]mW[Formula: see text]cm2. Vivid visualizations of capillaries and vessels in a mouse brain were also obtained with low background and high contrast. Because of cheaper instruments and safer power density, the NIR two-photon luminescence of NaYF4:Yb[Formula: see text]Tm@NaYF4 upconversion NPs could promote wider application of two-photon technology. The modified multilayer coating method could be widely used for upconversion NPs to increase the stable time of the in vivo circulation. Our work possesses a great potential for deep imaging and imaging-guided treatment in the future.

Semiconductor plasmon enhanced monolayer upconversion nanoparticles for high performance narrowband near-infrared photodetection

Employing lanthanide doped upconversion nanoparticles (UCNPs) as near-infrared absorbing photoactive materials is a feasible conception for constructing high efficient and stable narrowband wavelength-selective photodetectors, but limited by its upconversion luminescence efficiency. Herein, we experimentally and theoretically demonstrate upconversion luminescence (UCL) enhancement in monolayer UCNPs using plasmon semiconductor NPs (CsxWO3) and further explore its narrowband near-infrared photodetection application. The UCL improvement of 144 folds in CsxWO3/NaYF4/NaYF4:Yb3+, Er3+ hybrid was realized with the optimized spacer thickness (15 nm) and monolayer UCL. More than three orders enhancement was obtained via the semiconductor plasmon combined with core-shell UCNPs in both CsxWO3/NaYF4/monolayer-NaYF4:Yb3+, Er3+@NaYF4:Yb3+, Tm3+ and CsxWO3/NaYF4 /monolayer-NaYF4:Yb3+, Tm3+@NaYF4:Yb3+, Er3+. Interestingly, the higher enhancement of core's emissions was recorded in core-shell UCNPs by coupling with CsxWO3 NPs. The excitation field amplification dominates the high UCL enhancement, revealed by the UCL dynamics and the calculated electric field intensity. Finally, the high performance narrow photodetectors for 980 nm is constructed employing MAPbI3/CsxWO3/NaYF4/NaYF4:Yb3+, Er3+@NaYF4:Yb3+, Tm3+ hybrids, with narrow line width of 20 nm, high responsivity of 0.33 A/W, detectivity of 4.5 × 1010 Jones, and short response time of 180 ms, which is much better than the previous photodetectors. This finding provides keen approach for developing high efficient/performance UCNPs and narrowband photodetectors.

High performance perovskite solar cells based on β-NaYF4:Yb3+/Er3+/Sc3+@NaYF4 core-shell upconversion nanoparticles

The introduction of upconversion materials as spectral converter into photovoltaic devices to harvest and convert near infrared photons to visible photons that can thus be absorbed by perovskite layer is a promising strategy for enhancing the performance of perovskite solar cells. Hence, β-NaYF4:Yb3+/Er3+/Sc3+@NaYF4 rare-earth doped upconversion nanoparticles with core-shell structure are synthesized. The doped rare-earth ions Yb3+ and Er3+ convert near infrared light to red and green light, and the Sc3+ ions enhance the upconversion luminescence efficiency, which broaden the absorption range of solar irradiation and generate extra photocurrent in the solar cells. The surface defects of β-NaYF4:Yb3+/Er3+/Sc3+ is passivated by the even NaYF4 shell, which results in the obvious enhancement in upconversion emission intensity. Consequently, the perovskite solar cell based on the rare-earth doped upconversion nanoparticle mesoporous layer achieves a high power conversion efficiency of 20.19%, while the device based on TiO2 mesoporous layer gets an efficiency of 17.44%.

Graphene-Conjugated Upconversion Nanoparticles as Fluorescence-Tuned Photothermal Nanoheaters for Desalination

Multiphoton (980 nm) absorbing lanthanide doped upconversion nanoparticles (UCNPs) are emerging as fluorophores and photothermal agents but are limited by the low quantum yield of their visible flu...

Rational synthesis of three-dimensional core-double shell upconversion nanodendrites with ultrabright luminescence for bioimaging application.

Engineering the morphology of rare-earth doped NaYF4-based upconversion nanoparticles (UCNPs) can effectively tune their upconversion luminescence emission (UCLE) properties. Herein, we rationally synthesized a new class of three-dimensional upconversion core-double-shell nanodendrites (UCNDs) including an active core (NaYF4:Yb,Er,Ca) capped by a transition layer (NaYF4:Yb,Ca) and an active outer shell (NaNdF4:Yb,Ca). The high concentration of the Nd3+ sensitizer in the outer dendritic shell enhances the luminescence intensity, while the transition layer enriched with Yb3+ acts as an efficient energy migration network between the outer shell and inner core along with preventing the undesired quenching effects resulting from Nd3+. These unique structural and compositional merits enhanced the UCLE of UCNDs by 5 and 15 times relative to NaYF4:Yb,Er,Ca@NaYF4:Yb,Ca truncated core-shell UCNPs and NaYF4:Yb,Er,Ca spherical core UCNPs, respectively, under excitation at 980 nm. The SiO2-COOH layer coated UCNDs (UCND@SiO2-COOH) were successfully used as efficient long-term luminescent probes for in vitro and in vivo bioimaging without any significant toxicity. The uptake and retention of UCND@SiO2-COOH were mostly found in the liver and spleen. This study may open the way towards the preparation of three-dimensional UCND nanostructures for biomedical applications.

Yb,Nd,Er-doped upconversion nanoparticles: 980 nm versus 808 nm excitation

Yb,Nd,Er-doped upconversion nanoparticles (UCNPs) have attracted considerable interest as luminescent reporters for bioimaging, sensing, energy conversion/shaping, and anticounterfeiting due to their capability to convert multiple near-infrared (NIR) photons into shorter wavelength ultraviolet, visible or NIR luminescence by successive absorption of two or more NIR photons. This enables optical measurements in complex media with very little background and high penetration depths for bioimaging. The use of Nd3+ as substitute for the commonly employed sensitizer Yb3+ or in combination with Yb3+ shifts the excitation wavelength from about 980 nm, where the absorption of water can weaken upconversion luminescence, to about 800 nm, and laser-induced local overheating effects in cells, tissue, and live animal studies can be minimized. To systematically investigate the potential of Nd3+ doping, we assessed the performance of a set of similarly sized Yb3+,Nd3+,Er3+-doped core- and core-shell UCNPs of different particle architecture in water at broadly varied excitation power densities (P) with steady state and time-resolved fluorometry for excitation at 980 nm and 808 nm. As a measure for UCNPs performance, the P-dependent upconversion quantum yield (ΦUC) and its saturation behavior were used as well as particle brightness (BUC). Based upon spectroscopic measurements at both excitation wavelengths in water and in a lipid phantom and BUC-based calculations of signal size at different penetration depths, conditions under which excitation at 808 nm is advantageous are derived and parameters for the further optimization of triple-doped UCNPs are given.

Fluorescence fiber optic temperature sensor based on fused upconversion luminescent nanoparticles.

A new type of fluorescence fiber optic temperature sensor based on the detection of fluorescence intensity ratio (FIR) is proposed. Benefited from the temperature-dependent characteristic of upconversion luminescence (UCL), it can be applied in fiber optic temperature sensors. Rare earth doped upconversion nanoparticles (UCNPs) NaYF4:Er3+,Yb3+ are embedded in a multi-mode quartz fiber through the technology of fiber fusion as the sensing unit of temperature sensors. A 980 nm laser is used to stimulate UCL in a temperature range from 40 °C to 100 °C. Experimental validation and spectral analysis are carried out to confirm the rationality of sensors' design. Results show that FIR changes with the temperature in Boltzmann distribution law. The sensitivity of the temperature sensors can reach the value between 0.0087 and 0.0144 K-1.

Upconversion Nanoprobes: Recent Advances in Sensing Applications.

Rare earth ions doped upconversion nanoparticles (UCNPs) are capable of stepwisely converting two or more lower energy near-infrared (NIR) excitation photons into a higher energy visible and ultraviolet emission photon, resulting in a large anti-Stokes shift of several hundred nanometers. Because the f-electron configurations of lanthanide ions have abundant energy levels, and many of them possess long lifetimes, UCNPs exhibit unique optical properties including optical tunability over emission wavelengths and lifetimes, better photo-stability and improved monochromatic color-purity and spatial resolution. However, the low luminescent efficiency, largely owing to their substantially weak and narrow band absorptions, has greatly hampered the translation of UCNPs-based technologies from the academic stage to real world products. Recently, increasing efforts have been paid on boosting the upconversion luminescence brightness and efficiency, including inert shells coating, high concentration of activators dop...

Selective Polarization Modification of Upconversion Luminescence of NaYF4:Yb3+,Er3+ Nanoparticles by Plasmonic Nanoantenna Arrays

Rare-earth ions doped upconversion nanoparticles (UCNPs) have received great attention for the promising applications ranging from bioimaging and sensing to lighting and displaying technology. Meanwhile, active control of polarization state of the upconversion luminescence (UCL) of UCNPs is also significant in the applications such as polarization microscopy and 3D display. Here, we report the polarization modification for the UCL of β-NaYF4:Yb3+,Er3+ nanoparticles by selectively matching the localized surface plasmon resonance (LSPR) of the rectangular plasmonic slot nanoantenna array to the spectrum of the UCL. The plasmonic resonance band centered at 650 nm of the nanoantenna array realized a strong polarization nature of the selected UCL around 660 nm with the degree of linear polarization up to ∼80%, which stems from the interaction between the 660 nm emission band of UCNPs and the plasmonic modes of the rectangular slot nanoantenna array. Meanwhile, the UCL at 550 nm remained unpolarized due to the ...