Upconversion Particles Research Articles

Unlocking Single-Particle Multiparametric Sensing: Decoupling Temperature and Viscosity Readouts through Upconverting Polarized Spectroscopy.

Upconverting particles (UCPs), renowned for their capability to convert infrared to visible light, serve as invaluable imaging probes. Furthermore, their responsiveness to diverse external stimuli holds promise for leveraging UCPs as remote multiparametric sensors, capable of characterizing medium properties in a single assessment. However, the utility of UCPs in multiparametric sensing is impeded by crosstalk, wherein distinct external stimuli induce identical alterations in UCP luminescence, hindering accurate interpretation, and yielding erroneous outputs. Overcoming crosstalk requires alternative strategies in upconverting luminescence analysis. In this study, it is shown how a single spinning NaYF4:Er3+, Yb3+ upconverting particle enables simultaneous and independent readings of temperature and viscosity. This is achieved by decoupling thermal and rehological measurements-employing the luminescence of thermally-coupled energy levels of Er3+ ions for thermal sensing, while leveraging the polarization of luminescence from non-thermally coupled levels of Er3+ ions to determine viscosity. Through simple proof-of-concept experiments, the study validates the capability of a single spinning UCP to perform unbiased, simultaneous temperature, and viscosity sensing, thereby opening new avenues for advanced sensing in microenvironments.

NIR‐induced upconversion‐assisted photopolymerization: Key factors, challenges, and future directions

AbstractNIR‐induced upconversion‐assisted photopolymerization has gained growing attention in the past two decades because of its numerous advantages over conventional UV/visible photopolymerization and two‐photon polymerization processes. However, research in this area is still in its early stages. To extend the practical application of NIR‐induced radiation curing, it is essential to optimize the factors affecting the photopolymerization reactions. Researchers have been constantly trying to improve these factors to tune the photo‐physical characteristics (luminescence intensity and color) of upconversion particles (UCPs), enhance curing depths and degree of double bond conversion (DC), and investigate the application of UCPs in emerging fields. In this review, first, a brief discussion of the upconversion mechanisms and upconversion efficiency is provided. Then, a detailed discussion of the factors influencing the upconversion‐assisted photopolymerization comprising UCP nature and characteristics, UCP content, presence of fillers/pigments/additives, laser intensity, photoinitiator content, and maximum absorption wavelength of photoinitiator is provided, and recent progress in improving these factors is presented. Finally, the advantages and drawbacks of the UC‐initiated polymerization are discussed, and perspectives for future directions are suggested.Highlights NIR‐induced upconversion‐assisted photopolymerization garners growing interest. Influential factors in upconversion‐assisted photopolymerization are thoroughly discussed. The recent progress on improving these factors and the future directions are provided.

Construction of fiber-reinforced composites with high-thickness: Achieving enhanced interfacial and mechanical properties through upconversion particles assisted near-infrared photopolymerizaton

Glass fiber reinforced polymer-based composites prepared by photocuring technology offer notable advantages. However, the traditional UV curing technology faces challenges in balancing curing efficiency, penetration depth, and mechanical properties when producing high-thickness fiber-reinforced composites. This study introduced a new method for crafting thick glass fiber reinforced composites via upconversion particle-assisted near-infrared photopolymerization (UCAP). Near-infrared (NIR) radiation had superior penetration in glass fiber composites system, effectively curing of specimens exceeding 20 mm in thickness. Through micro-CT and atomic force microscopy, it was verified that UCAP specimens had fewer interfacial defects and a wider interphase, making contribution to enhanced interlaminar and interfacial shear strength. Additionally, uniform curing effectively alleviated stress concentration under external forces, resulting in a 78.5 % increase in flexural strength and a 32.1 % increase in impact toughness for UCAP specimens compared to UV-cured ones. This approach facilitated rapid outdoor curing of large-sized glass fiber composites with sustained structural stability, showcasing the potential application of UCAP in high-performance glass fiber composites rapid prototyping.

An ultrasensitive dual-mode aptasensor for patulin based on the upconversion particles and G-Quadruplex-hemin DNAzyme

Patulin (PAT) is a mycotoxin-produced secondary metabolite that can contaminate foods, causing toxic effects on animal and human health. Therefore, for the first time, we have constructed a “turn-on” dual-mode aptamer sensor for PAT using oleic acid-coated upconversion nanomaterials (OA-UCNPs) and G-Quadruplex-hemin DNAzyme (G4-DNAzyme) as fluorescent and colorimetry probes. The sensor employs aptamers binding to PAT as recognition elements for specific molecule detection. Mxene-Au can be used as a biological inducer to assist OA-UCNPs in controlling fluorescence intensity. In addition, colorimetric signal amplification was performed using the trivalent G4-DNAzyme to increase detection sensitivity and reduce false positives. Under optimal conditions, the dual-mode aptasensor has a detection limit of 5.3 pg mL−1 in fluorescence and 2.4 pg mL−1 in colorimetric methods, respectively, with the wider linear range and limit of detection (LOD) of the colorimetric assay. The combination aptasensor can detect PAT with high sensitivity and high specificity and has broad application prospects in the field of food safety detection.

Yb3+/Er3+ co-doped Mg-substituted tricalcium phosphate upconversion materials for bioimaging

Yb3+ and Er3+ co-doped Mg-substituted tricalcium phosphate (Mg-TCP) upconversion particles were synthesized using a two-step process: Single-phase Mg-TCP-Yb3+/Er3+ materials with an average particle size ∼ 130.2 nm can be obtained by the hydrothermal reaction at 180 °C for 24 h, followed by heat treatment at 800 °C for 4 h, which demonstrated excellent upconversion green luminescence around the 520/550 nm wavelength. The culture of MC3T3-E1 cells with the extraction medium from Mg-TCP-8%Yb3+/Er3+@800°C materials showed obvious proliferation with increase of culture time and noncytotoxicity. Additionally, the intracellular imaging of Mg-TCP-8%Yb3+/Er3+@800°C through endocytosis by cells demonstrated that the particles can be significantly degraded within 24 h, which showed great potential for bioimaging applications.

Fresnel lens three-dimensionally printed on the facet of a single mode fiber for trapping, manipulation, and spectrum.

Fiber optical tweezers (FOTs) provide a functionality for micro-/nanoparticle manipulation with a slim and flexible optical fiber setup. An added in situ spectroscopic functionality can achieve characterization of the trapped particle, potentially useful for endoscopic, in-vivo studies in an inherently heterogeneous environment if the applicator end is all-fiber-built. Here, we demonstrate all-fiber optical tweezers (a-FOTs) for the trapping and in situ spectral measurement of a single, cell-sized microparticle. The key to ensure the simultaneous bifunctionality is a high numerical aperture (NA) Fresnel lens fabricated by two-photon direct laser writing (DLW) corrected by grid-correction methods. We demonstrate trapping and time-resolved, in situ spectroscopy of a single upconversion particle (UCP), a common fluorescent biomarker in biophotonics. The system achieves a 0.5-s time resolution in the in situ spectral measurement of a trapped UCP. The all-fiber designed system preserves the advantages of flexibility and robustness of the fiber, potentially useful for in-vivo biomedical studies such as cell-to-cell interactions, pH and temperature detection, and nucleic acids detection.

Planar technology fabrication of high-density luminescence structure based on NaYF4 microparticles

This study presents a technological capability of producing individual size-defined luminescent centers and high-density arrays of upconversion particles using monosize powder based on NaYF4 matrix doped with rare earth metals such as erbium and ytterbium. The integration of various techniques such as lithography, etching, and deposition has enabled the creation of cavity arrays, or trenches, with arbitrary shapes for localization of luminescent monodisperse microparticles with an average size of 1.65 μm.

Estimation of the proximal temperature rise of an excited upconversion particle by detecting the wavefront of emission.

Monitoring the temperature distribution within a local environment at the micro and nanoscale is vital as many processes are solely thermal. Various thermometric techniques have been explored in the community, and out of these, fluorescent nano/micro particle-based mechanisms are accepted widely (fluorescence intensity ratio (FIR) techniques, where the ratio of populations in two consecutive energy levels is compared with Boltzmann distribution). We describe a new technique to account for the temperature rise near an illuminated upconverting particle (UCP) using wavefront imaging, which is more sensitive than the conventional thermometric techniques on the microscale. We rely on a thermo-optical phase microscopic technique by reconstructing the wavefront of emission from an upconverting particle using a Shack-Hartmann wavefront sensor. The wavefront maps the local phase distribution, which is an indicator of the surroundings' optical parameters, particularly the suspended medium's temperature-induced refractive index in the presence of convection currents. We describe how these extracted phase values can provide information about the optical heating due to the particle and hence its local environment along the direction of the emission. Our findings demonstrate the detection of a minimum temperature rise of 0.23 K, while the FIR methods indicate a minimum of 0.3 K rise. This technique is used to study the temperature increase in the backscattered direction for an upconverting particle illuminated on pump resonance. We also estimate the Soret coefficient for an upconverting particle optically trapped on pump resonance and experiencing anisotropic heating across the body.

Application of upconversion nanoparticles as a thermal sensor for biological tissue

The paper shows the possibility of simultaneous registration of the temperature of nanoparticles embedded in the fat layer and temperature-induced phase transitions in the fat layer. The luminescence spectra of upconversion particles (UCNPs) were measured and analyzed in a wide temperature range: from room to physiological and further to a hyperthermic temperature resulting in tissue morphology change. Typical samples thickness of adipose tissue was 0.5 mm. The sample temperature varied between 25 °C and 60 °C. The temperature dependence of the UCNPs luminescence intensity from UCNPs deposited onto the sample surface (1 layer) and from UCNPs deposited between two layers of abdominal adipose tissue was recorded. In the course of adipocyte heating, lipids of fat droplet first transit from a crystalline form to a liquid crystal form and then to a liquid form, which is characterized by much less scattering. The high-temperature transition is recorded most well. The obtained results confirm a high sensitivity of the luminescent UCNPs to the temperature variations within tissues and show a strong potential for the controllable tissue thermolysis.

Upconversion particle-assisted NIR polymerization enables microdomain gradient photopolymerization at inter-particulate length scale

High crosslinking and low shrinkage stress are difficult to reconcile in the preparation of performance-enhancing photopolymer materials. Here we report the unique mechanism of upconversion particles-assisted NIR polymerization (UCAP) in reducing shrinkage stress and enhancing mechanical properties of cured materials. The excited upconversion particle emit UV-vis light with gradient intensity to the surroundings, forming a domain-limited gradient photopolymerization centered on the particle, and the photopolymer grows within this domain. The curing system remains fluid until the percolated photopolymer network is formed and starts gelation at high functional group conversion, with most of the shrinkage stresses generated by the crosslinking reaction having been released prior to gelation. Longer exposures after gelation contribute to a homogeneous solidification of cured material, and polymer materials cured by UCAP exhibit high gel point conversion, low shrinkage stress and strong mechanical properties than those cured by conventional UV polymerization techniques.

Facets of optically and magnetically induced heating in ferromagnetically doped-NaYF4 particles

Upconverting particles like Yb and Er-doped NaYF4 are known to heat up after illumination with light at pump wavelength due to inefficient upconversion processes. Here we show that NaYF4 particles which have been co-doped not only with Yb and Er but also Fe improves the photothermal conversion efficiency. In addition, we show for the first time that alternating magnetic fields also heat up the ferromagnetic particles. Thereafter we show that a combination of optical and magnetic stimuli significantly increases the heat generated by the particles.

Upconversion Luminescence Response of a Single YVO4:Yb, Er Particle.

We present the results of the luminescence response studies of a single YVO4:Yb, Er particle of 1-µm size. Yttrium vanadate nanoparticles are well-known for their low sensitivity to surface quenchers in water solutions which makes them of special interest for biological applications. First, YVO4:Yb, Er nanoparticles (in the size range from 0.05 µm up to 2 µm), using the hydrothermal method, were synthesized. Nanoparticles deposited and dried on a glass surface exhibited bright green upconversion luminescence. By means of an atomic-force microscope, a 60 × 60 µm2 square of a glass surface was cleaned from any noticeable contaminants (more than 10 nm in size) and a single particle of 1-µm size was selected and placed in the middle. Confocal microscopy revealed a significant difference between the collective luminescent response of an ensemble of synthesized nanoparticles (in the form of a dry powder) and that of a single particle. In particular, a pronounced polarization of the upconversion luminescence from a single particle was observed. Luminescence dependences on the laser power are quite different for the single particle and the large ensemble of nanoparticles as well. These facts attest to the notion that upconversion properties of single particles are highly individual. This implies that to use an upconversion particle as a single sensor of the local parameters of a medium, the additional studying and calibration of its individual photophysical properties are essential.

Employing NaYF4: Yb, Tm upconversion particles (UCPs) in combination with rGO and PANI nanomaterials for the fabrication of radiation-curable anticorrosion composites/coatings

Upconversion particles (UCPs) able to emit photons from the ultraviolet to near-infrared (NIR) region of the electromagnetic spectrum when excited by a NIR laser may be used as internal radiation sources for the manufacture of thick composites with uniform and deep polymerization. In this work, NaYF4: Yb, Tm-based UCPs were synthesized and employed to cure composites using a dual curing method via UV and blue light produced from the UCPs to activate the photo-initiators (PIs), and the resulting cure depth and degree of double bond conversion (DC) were measured. In addition, the influence of UCP content and laser power on cure depth and DC was investigated. The emission rate of the UCPs demonstrated a non-linear, wavelength-specific relationship with increasing laser power and exposure time. Using optimal conditions, 62 % DC with a 2.5 cm cure depth was achieved. For the first time, the ability of UCPs to cure composites in the presence of reduced graphene oxide (rGO) and polyaniline (PANI) nanoparticles was studied. Results indicated that DC was almost consistent across samples (except the sample containing 1 wt% rGO), although the addition of nanomaterials decreased DC and cure depth. The addition of 0.5–0.5 wt% rGO-PANI increased the nanocomposites' compressive strength and strain at failure by 66 and 37 %, respectively. The nanocomposite formulations were applied to steel and the anti-corrosion properties were also investigated. The findings revealed low-frequency impedance (|Z|10 mHz) numbers higher than 1010 Ω.cm2 up to 4 w immersion duration, proving this coating's exceptional barrier anti-corrosion capabilities.

Excellent Sensitive Temperature Sensing Performance Based on Fluorescence Intensity Ratio Technique of Yb3+/Er3+ Codoped Gd2(WO4)3

For noncontact temperature sensing, the fluorescence intensity ratio (FIR) technique based on thermally coupled levels has great prospects. Within this technique, Yb3+/Er3+ codoped upconversion (UC) particles are regarded as efficient material. Juanqin Xue and co-workers (article number 2200471) have prepared Yb3+/Er3+ codoped Gd2(WO4)3 particles by a facile coprecipitation method and subsequent calcination. The crystal structure, microstructure, and UC emission of the particles are studied in detail, and the optimum temperature sensing performance is systematically measured. Excellent temperature-sensitive properties of Gd2(WO4)3:Yb3+/Er3+ demonstrate great potential for its application in noncontact optical temperature sensors.

Excellent Sensitive Temperature Sensing Performance Based on Fluorescence Intensity Ratio Technique of Yb3+/Er3+ Codoped Gd2(WO4)3

The efficient upconversion (UC) particles based on fluorescence intensity ratio (FIR) technique are developed for application in novel temperature sensors. Herein, Yb3+/Er3+‐codoped Gd2(WO4)3 particles are prepared by coprecipitation method and subsequent calcination. The phase structure and surface morphology of the particles are systematically analyzed. The UC emission spectrum of Gd2(WO4)3:Yb3+/Er3+ particles are mainly composed of two strong emission bands centered at 530 and 551 nm, respectively. Moreover, the optimum doping concentration of Yb3+ and Er3+ is fixed at 10% and 2%, respectively. UC emission mechanism based on two‐photon process is investigated by studying the pump power excitation dependence and fluorescence decay behavior of Gd2(WO4)3:10%Yb3+/2%Er3+ particles. The excellent temperature sensing capability of Gd2(WO4)3:10%Yb3+/2%Er3+ particles is implemented from thermally coupled levels (TCLs) of Er3+. Notably, the maximum absolute sensitivity (S a) and relative sensitivity (S r) based on TCLs by 2H11/2/4S3/2 levels are 1.39 %K−1 (at 518 K) and 1.18 %K−1 (at 293 K), respectively. As a result, Gd2(WO4)3:10%Yb3+/2%Er3+ particles have a great potential for application in noncontact temperature sensors.

Near-infrared light induced curing of electrically conductive adhesive assisted by upconversion particles

We report a highly-efficient method for preparing an electrically conductive adhesive (ECA) by using the upconversion nanoparticle-assisted near infrared photopolymerization (UCAP) technology.

Infrared imaging of polydimethylsiloxane-doped upconversion particle composites.

Short-wave infrared imaging is playing an increasingly important role in present scientific research. However, the high experimental cost limits its application. Based on the upconversion fluorescence effect, we prepared a low-cost composite film for short-wave infrared imaging using upconversion particles and polydimethylsiloxane. The imaging quality and stability of the prepared composite films are examined using an infrared laser. The fluorescence density fluctuation of the composite films at 100 is only 1.2%, and the maximum value of the fluorescence power percentage error caused by the inhomogeneity is only 4.5%. Due to the affordable and easy accessibility, a typical optical laboratory can prepare and use the aforementioned technique in experiments in a short time.

Near-infrared Induced Cationic Photopolymerization: A Versatile Method for Preparing Thick Polymer Materials

Cationic polymerization has been a versatile tool for the preparation of polymer materials. However, deep cationic photopolymerization remains a great challenge due to color deposition. Using upconversion particles as internal lamps to convert near-infrared (NIR) light into blue light, we report a versatile and efficient strategy to achieve deep cationic photopolymerization of epoxy monomers. Under NIR light excitation, the final functional group conversion of the monomer was as high as 80%, much higher than the 50% for the UV-irradiated system. The maximum temperature during upconversion particle-assisted photopolymerization was around 100 °C, comparable to or lower than some reported frontal cationic photopolymerization. Materials up to 2.5 cm thickness and free of defects and bubbles were obtained by 980 nm laser irradiation.

NaYF4 upconversion crystals with red light emission by low Er3+ concentration doping

In the work, a range of Er3+-sensitized NaYF4 upconversion (UC) particles doped with Tm3+ and Ho3+ are successfully prepared by hydrothermal process. The UC crystals appear two green emission peaks at 529 and 541 nm and a remarkable red emission peak at 655 nm under 980 and 1532 nm irradiations. Here, Tm3+ and Ho3+ serve as trapping centers, which confine the excitation energy efficiently to promote the red UC emission and improve the red to green ratio. UC mechanisms in the Er3+/Tm3+ co-doped and Er3+/Ho3+ co-doped NaYF4 crystals are discussed at length based on the UC luminescence spectroscopy. Unlike the traditional sensitization with high Er3+ concentration doping to obtain red light, the red UC luminescence is acquired by low Er3+ concentration doping, which can effectively avoid concentration quenching caused by high Er3+ concentration doping. Furthermore, NaYF4:Er3+, Tm3+ crystals exhibit stronger red UC emission compared with NaYF4:Er3+, Ho3+ counterparts. Er3+-sensitized NaYF4 crystals doped with Tm3+ and Ho3+ ions generate pure red light more efficaciously under 1532 nm excitation than under 980 nm excitation. The phosphors emitting brilliant red UC emission have the potential applications in solid state lasers and biological imaging.

NIR-Driven White Light Diode Formed with UCNP@AIEgen Nanocomposites

Upconversion nanoparticles (UCNPs) and polymerizable molecules of aggregation-induced emission (AIE) were combined to produce white light emission. Blue and ultraviolet light-emitting doped lanthanide UCNPs (LiYF4:Yb3+/Tm3+@LiYF4:Yb3+), polymerizable red light-emitting 1,4-bis(piperidinyl-1-propenyl bromide)anthracene (1,4-BPPA), and green light-emitting 9,10-BPPA AIE molecules were mixed with photopolymerizable acrylate oligomers for photopolymerization to form a luminescent film. The fluorescence spectrum, obtained by exciting the LiYF4:Yb3+/Tm3+@LiYF4:Yb3+ UCNPs with 980 nm near-infrared light, exhibited visible light emission, and high-energy emission included ultraviolet light at 365 nm and blue light at 450 and 475 nm. The high-energy light produced through the transfer of energy from the UCNPs excited 1,4-BPPA and 9,10-BPPA molecules to emit red and green light, thus producing a hybrid of red, blue, and green light emission that resulted in white light. X-ray diffractometry, scanning electron microscopy, ultraviolet–visible spectrometry, and fluorescence spectrometry were used to analyze the materials. The CIE coordinates of the white light-emitting film were (0.3358, 0.3536), corresponding to a correlated color temperature of 5370 K. The results demonstrate that upconversion particles and polymerizable AIE molecules can be combined to fabricate a white light-emitting diode film.