Upconversion Luminescent Nanocrystals Research Articles

Wide-range optical fiber temperature sensor based on up-conversion luminescent nanocrystals.

In this study, an optical fiber temperature sensor based on up-conversion luminescence (UCL) is proposed. The core part is a new plan of the sensing unit, which is constructed with UCL materials of NaYF4: Yb3+, Er3+ nanocrystals by fiber fusion technology to achieve a wide range of temperature measurements. Experimental results show that the proposed optical fiber temperature sensor shows significant spectrum-temperature characteristics in 80-373 K temperature range. Its relative sensitivities at low temperature and normal temperature are 2.2×10-3/K with a determination coefficient of 0.957 and 9.1×10-3/K with a determination coefficient of 0.994, respectively. This type of sensor also has good mechanical strength and system stability and shows great potential for development, particularly in the aerospace field with large temperature differences.

Fabrication of NaYF4:Yb3+,Tm3+-modified Ag nanocubes with upconversion luminescence and photothermal conversion properties.

Herein, uniform Ag nanocube@NaYF4:Yb3+,Tm3+ multifunctional nanocomposites were constructed by a facile synthetic strategy. Following the successful synthesis of Ag nanocubes, cubic phase NaYF4:Yb3+,Tm3+ upconversion luminescent nanocrystals were modified on the surface of the Ag nanocubes, enhanced the mutual assistance of energy and versatility of the materials. Upon irradiation with a near-infrared laser, the nanocomposites exhibited excellent upconversion fluorescence and good photothermal conversion capability. Furthermore, the potential biological applications and biosafety of the Ag@NaYF4:Yb3+,Tm3+ nanocomposites were also demonstrated; the obtained nanocomposites could achieve a good bactericidal performance and photothermal treatment of cancer cells, and they could be potentially applied in the biomedical field as a promising agent. Furthermore, this method provides a facile approach for synthesizing a multifunctional nanocomposite with different properties.

Enhanced photocatalytic activity of TiO2 in visible and infrared light through the synergistic effect of upconversion nanocrystals and quantum dots

The synergy of up-conversion luminescence nanocrystals NaYF4:Yb,Tm and CdS quantum dots(CdS QDs) is used to improve the photocatalytic activity of TiO2 in visible and infrared light. The photocatalyst was fabricated with the water-soluble NaYF4:Yb,Tm nanocrystals as the core and anatase-TiO2 as the shell. Then CdS QDs were deposited on the surface of shell TiO2 by hydrothermal method. The photocatalytic activity of the prepared NaYF4:Yb,Tm@TiO2/CdS QDs composite was investigated by photodegration of Rhodamine B under white, visible light and near-infrared light. When compositing TiO2 with the upconversion NaYF4:Yb,Tm, the photocatalytic activity of the NaYF4:Yb,Tm@TiO2 was 6.8 times to TiO2 under white light and 2.5 times to TiO2 under visible light. After coupling the upconversion effect and the quantum dots sensitization effect with TiO2, the photocatalytic activity of the NaYF4:Yb,Tm@TiO2/CdS QDs composite was significant 11.2 times to TiO2 under white light, and 6.5 times to TiO2 under visible light, respectively. Even more considerable enhancement was discovered under the near-infrared light. The NaYF4:Yb,Tm@TiO2/CdS QDs composite showed 1590 times relative to almost no activity of TiO2. The photocatalytic enhancement is attributed to two effects. First, the sensitization of CdS QDs can extend the absorption region of TiO2 to 490 nm. Secondly the upconversion NaYF4:Yb,Tm can absorb near-infrared light and emit ultraviolet (348 nm and 366 nm) absorbed by anatase-TiO2 and visible light (476 nm) absorbed by CdS QDs.

Phase controllable synthesis of NaMgF3:Yb3+, Er3+ nanocrystals with effective red upconversion luminescence

Synthesizing and controlling lanthanide ions doped upconversion luminescent nanocrystals with effective emission have been researched to satisfy the demand for different applications. In this work, the influence of reaction conditions on crystal composition and upconversion luminescence properties of NaMgF3:Yb3+, Er3+ nanocrystals have been explored with XRD and upconversion emission spectra. The experimental results demonstrate that lanthanide ions concentration has great impact on the growth of samples, i.e., a low concentration leads to cube NaMgF3 nanocrystals, while a high concentration facilitates impurity NaYbF4 microtube. Adjusting reaction parameters is also crucial for controlling NaMgF3 crystal structure by shortening reaction time and reducing reaction temperature. In addition, the well-dispersed NaMgF3:Yb3+, Er3+ nanocrystals with different red-to-green ratios have been achieved successfully by changing the reaction parameters, resulting in the upconversion luminescence from orange to red, and the single-band red UC luminescence can be observed in NaMgF3:0.5Yb3+, 0.5Er3+ nanocrystals. This study explains the formation mechanism of NaMgF3:Yb3+, Er3+ nanocrystals and gains the effective red luminescence, which may be helpful to synthesize other similar upconversion nanocrystals in colour display, bioimaging and so on.

Highly Secure Plasmonic Encryption Keys Combined with Upconversion Luminescence Nanocrystals

AbstractThis study proposes a novel and highly secure encryption technology based on plasmonic‐enhanced upconversion luminescence (UCL). The technology can be realized by a disordered plasmonic nanostructure composed of a transferred metal nanoparticle–UC nanocrystals (UCNC)–metal (tMUM) film using the graphene transfer process, in which the metal nanoparticles that formed on the graphene layer are transferred using Scotch tape. The plasmonic tMUM film strongly enhances the UCL by a factor of 200 mainly because of the excitation of the gap plasmon polaritons. Meanwhile, the UCNCs in direct contact with the metal film result in luminescence quenching caused by a nonradiative process. Herein, a highly secure anti‐counterfeit film is developed, which is very hard to duplicate and cannot be reused, using two conflicting features (i.e., emission enhancement and quenching phenomena). The UCL is strongly amplified only when the first (i.e., a random metal nanoparticle array) and second (i.e., UCNCs on a Ag film) codes are very precisely overlapped as designed, thereby generating the originally designed final code. Therefore, our novel high‐level security device is expected to be easily applied to protect and identify genuine products.

Fe3+-Enhanced NIR-to-NIR upconversion nanocrystals for tumor-targeted trimodal bioimaging

Fe3+-Enhanced NIR-to-NIR multifunctional upconversion luminescence nanocrystals were synthesized for excellent tumor-targeted UCL/MRI/X-ray trimodal bioimaging.

Development of novel upconversion luminescent nanoparticle of Ytterbium/Thulium–doped beta tricalcium phosphate

A novel class of upconversion luminescent nanocrystals of Yb/Tm:calcium deficient hydroxyapatite were synthesized by co-precipitation method in aqueous solution (pH adjusted to 6) and specially heat-treated with microwave radiation at different temperatures (from 900°C to 1000°C) and times (2–10min) to produce small nanocrystals of Yb/Tm:β-tricalcium phosphate (β-TCP). As a result, we report for the first time, a single-phase Yb/Tm-doped β-TCP nanocrystals with a mean crystallite size of 55.3nm. This material has an efficient visible luminescence from the 1G4 (blue emission) and 3F2 (red emission) and near infrared emission from the 3H4 excited states of Tm3+ induced by the Yb3+→Tm3+ energy transfer under laser excitation (Yb3+) at 972nm. This β-TCP activated by Yb3+ and Tm3+ ions constitutes a new nano-fluoroprobe that can be used as optical contrast agents, affording high resolution and sensitivity for visible-near infrared applications.

Spectral and spatial characterization of upconversion luminescent nanocrystals as nanowaveguides.

Lanthanide upconversion (UC) luminescent nanocrystals exhibit a uniquely sharp multiband emission over a broad spectral bandwidth covering the ultraviolet region to the near-infrared (NIR) region when subjected to NIR excitation, which is vital for multichannel optical communication using wavelength-division multiplexing to achieve high transmission rates. In this study, we experimentally and theoretically investigated the spectral and spatial characterization of a single NaYF4:Yb3+,Tm3+(Yb3+,Er3+) UC nanocrystal as a nanowaveguide. We suggest that a UC nanocrystal can be used as a nanowaveguide because it produces a range of output colors simultaneously and provides unaltered emission bands during propagation. Via the observation of single NaYF4:Yb3+,Tm3+(Yb3+,Er3+) UC nanocrystals, we found, for the first time, that a single UC nanocrystal exhibited wavelength- and position-dependent UC emissions. In addition, by adding Ag coating to the UC nanocrystal to act as a plasmonic waveguide and introducing a photonic crystal, the scattering loss of the UC emissions was significantly suppressed in the middle of the NaYF4 nanocrystal, indicating efficient light guiding through the UC nanocrystal. Our discovery provides a basic understanding of the use of UC nanocrystals as nanowaveguides at the single-nanoparticle level, expanding our knowledge of the performance optimization of UC nanomaterials.

Phase angle encoded upconversion luminescent nanocrystals for multiplexing applications.

Lanthanide-doped upconversion nanoparticles (UCNPs) are increasingly used as luminescent candidates in multiplexing applications due to their excellent optical properties. In the past, several encoding identities have been proposed for UCNPs, including emission colour, intensity ratio between different emission bands, colour spatial distribution, and luminescence lifetime. In this paper, a new optical encoding dimension for upconversion nanomaterials is developed by exploring their luminescence kinetics, i.e., the phase angle of upconversion luminescence in response to a harmonic-wave excitation. Our theoretical derivation shows that the phase angle is governed jointly by the rise and decay times, characterizing the upconversion luminescence kinetics. Experimentally, a full set of methods are developed to manage the upconversion luminescence kinetics, through which the rise and decay times can be manipulated dependently or independently. Furthermore, a large phase-angle space is achieved in which tens of unique codes can potentially be generated in the same colour channel. Our work greatly extends the multiplexing capacity of UCNPs, and offers new opportunities for their applications in a wide range such as microarray assays, bioimaging, anti-counterfeiting, deep tissue multiplexing labelling/detection and high-density data storage. In addition, the development of this luminescence kinetics-based optical encoding strategy is also instructive for developing multiplexing techniques using other cascade luminescent systems that inherently lack multi-spectral channels, such as triplet-triplet annihilation molecule pairs.

Synthesis and Characterization of KMnF3:Yb/Er@KMnF3 Upconversion Luminescent Nanocrystals.

A hydrothermal method has been developed for preparation of monodispersed and flake KMnF3 upconversion luminescent nanocrystals doped with Yb3+ and Er3+. The prepared nanocystals materials were characterized by XRD, EDX, SEM and TEM. The upconversion emission spectra show that the KMnF3:Yb/Er nanocrystals has a single-narrow-band emission centered at 660 nm. This is the firstly reported hydrothermal procedure for synthesis of the flake KMnF3 nanocrystals with single-narrow-band upconversion luminescence. Furthermore, a core-shell structure was introduced to synthesize the KMnF3:Yb/Er@KMnF3 nanocrystals and higher luminescence intensity was obtained.

White upconversion luminescence nanocrystals for the simultaneous and selective detection of 2,4,6-trinitrotoluene and 2,4,6-trinitrophenol.

A highly water stable and strong upconversion (UC) luminescence NaYF4@PSI-NH nanosensor for the simultaneous and selective detection of 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP) was successfully developed. Via the 980 nm near-infrared (NIR) irradiation, these nanosensors emit strong white UC luminescence with five typical emission peaks centered at 363, 455, 475, 546, and 654 nm. The UC emission at both 363 and 546 nm was quenched by the addition of TNT; however, the ratio of luminescence intensity at 363 nm to 546 nm (I363/I546) had no change with the increase of TNT concentration. Meanwhile, only violet UC emission at 363 nm was dramatically quenched via the addition of TNP, and the I363/I546 ratio is negatively proportional to the TNP concentration in the range of 0.01-4.5 μg/mL of TNP. On the other hand, the green UC emission intensity at 546 nm is in negative proportion to the concentration of TNT. Moreover, cyclohexane, toluene, and other nitroaromatics (such as 2,4-dinitrotoluene (DNT) and nitrobenzene (NB)) have no influence on the detection. Therefore, we developed a facile method for the simultaneous and selective detection of TNT and TNP in the mixture solution of nitroaromatics independent of complicated instruments and sample pretreatment.

Controllable Multicolor Upconversion Luminescence by Tuning the NaF Dosage

Multicolor upconversion (UC) luminescence of NaYF4:Yb(3+)/Er(3+) nanoparticles (NPs) was successfully tuned by simply controlling the NaF dosage. Unlike UC nanocrystals previously reported in the literature with multicolor emission obtained by varying the rare-earth dopants, the current work developed a new approach to tune the UC emission color by controlling the NaF concentration without changing the ratio and dosage of rare-earth ions. TEM and powder XRD were used to characterize the shape, size, and composition of the UC luminescent nanocrystals. The luminescence images, emission spectra, and multicolor emission mechanism of the NPs have also been demonstrated. As a result of the excellent ability of this new method to manipulate color emission, this will open up new avenues in the areas of bioprobes, light-emitting devices, color displays, lasers, and so forth. To demonstrate their biological applications, the water-stable, biocompatible, and bioconjugatable NaYF4:Yb(3+)/Er(3+) @poly(acrylic acid) NPs were synthesized by this developed strategy and applied in targeted-cell UC luminescence imaging.

Synthesis and characterization of Yb 3+,Tm 3+:Ba 2YF 7 nanocrystalline with efficient upconversion fluorescence

A novel upconversion luminescence nanocrystals Yb 3+,Tm 3+:Ba 2YF 7 were synthesized via the hydrothermal method. They have uniform morphology with a mean size of 30 nm even if annealed at 600 °C. Pumped by 980 nm laser diode the as-synthesized powers emit ultraviolet/blue light, which is in the range of the specific upconversion luminescent spectra of Tm 3+ ions. After post-annealing at 600 °C in an argon atmosphere for 2 h, their upconversion luminescence intensity is 5 multiple improved and the ultraviolet/blue light can even be seen by the naked eyes under a low excitation power of 20 mW. This indicates that Ba 2YF 7 is a very effective luminescent host material. Excitation power dependences of individual upconversion emission intensity are plotted, which partly uncover the upconversion luminescence mechanism of Tm 3+ ions.