Upconversion Luminescence Intensity Research Articles

Solvothermal synthesis and upconversion luminescence of ultra-small Sc2O3: Yb, Er nanoparticles

Monodisperse sub-10 nm Sc2O3: Yb, Er upconverting nanoparticles (UCNPs) were firstly synthesized via solvothermal method in three-neck round-bottom flask. The X-ray diffraction (XRD) shows that the prepared UCNPs possess cubic structure. The transmission electron microscopy (TEM) shows that sample has monodisperse spheroid morphology with high crystallinity. The average size of spheroid UCNPs could be controllable manipulated as small as 3 nm. Furthermore, the sample exhibits stronger red and green upconversion luminescence (UCL) than reported Sc2O3: Yb, Er nanostructure by biphasic solvothermal method. The Fourier-transform infrared (FTIR) spectra and decay curve reveal that ultra-small Sc2O3: Yb, Er UCNPs exhibit the reduced surface groups and long decay time of Er3+ ions. The results indicate Sc2O3: Yb, Er UCNPs is a probable oxide material with small size and intense UCL for biological applications.

Selective optosensing of iron(III) ions in HeLa cells using NaYF4:Yb3+/Tm3+ upconversion nanoparticles coated with polyepinephrine.

Novel polyepinephrine-modified NaYF4:Yb,Tm upconversion luminescent nanoparticles (UCNP@PEP) were prepared via the self-polymerization of epinephrine on the surfaces of the UCNPs for selective sensing of Fe3+ inside a cell and for intracellular imaging. The proposed UCNP@PEP probe is a strong blue light emitter (λmax = 474nm) upon exposure to an excitation wavelength of 980nm. The probe was used for detecting Fe3+ owing to the complexation reaction between UCNP@PEP and Fe3+, resulting in reduced upconversion luminescence (UCL) intensity. The proposed probe has a detection limit of 0.2μM and a good linear range of 1-10μM for sensing Fe3+ ions. Moreover, the UCNP@PEP probe displays high cell viability (90%) and is feasible for intracellular imaging. The ability of the probe to sense Fe3+ in a human serum sample was tested and shows promising output for diagnostic purposes. The prepared UCNP@PEP probe was characterized by using UV-visible (UV-Vis) absorption spectrometry, fluorescence (FL) spectrometry, field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR).

Combined Detection of C-Reactive Protein and Serum Amyloid A Based on Up-Conversion Luminescent System for Internet of Medical Things Application

The combined detection of C-reactive protein (CRP) and serum amyloid A (SAA) is of great value in early diagnosis of infantile infectious diseases and the differentiation of bacterial and viral infections; however, conventional detection methods, such as electrochemical immunoassay, are costly and time-consuming, and not conducive to the application. In this paper, we report a miniature up-conversion luminescent system that exploits up-conversion nanoparticles (UCNPs) as fluorescent markers and uses the principle of lateral flow immunochromatography to detect CRP and SAA. The concentrations of CRP and SAA were obtained by analyzing the luminescence intensity of up-conversion luminescence excited by UCNPs. Using this system, the detection limit of CRP and SAA reached 0.05 ng/mL and 0.05 ng/mL, respectively, with high sensitivity and stability. In addition, the system can also interconnect with cloud-enabled smartphones through Bluetooth to realize Internet of medical things applications. The up-conversion luminescent system has the advantages of portability, rapid analysis, accuracy, and low cost. Thus, there is great potential for the monitoring of inflammatory diseases and mobile health management in point-of-care testing.

Local-structure-dependent luminescence in lanthanide-doped inorganic nanocrystals for biological applications.

Lanthanide-doped inorganic nanocrystals, possessing superior luminescence performance and photochemical stability, have attracted considerable attention due to their promising biological applications such as in bioimaging, biodetection, biotherapeutics and temperature sensing. Great progress has been made in achieving distinct and tailored optical properties for these functional nanocrystals in the past few decades. In this feature article, we summarize our recent advances in the realization of desirable and tunable luminescence for lanthanide-doped inorganic nanocrystals through local structure engineering that includes two main strategies, namely, externally morphological architecture design and intrinsically crystal structure regulation. As for the externally morphological architecture design, distinct optical performance achieved in lanthanide-doped nanocrystals with varied morphologies like core-shell, hollow and ultrasmall nanoarchitectures is summarized. With regard to the intrinsically crystal structure regulation, the tunable upconversion luminescence intensity and red-to-green ratio of Er3+ for Yb3+/Er3+-doped nanocrystals and the consequent biodegradable nanocrystals are discussed, with an emphasis on the origin underlying the crystal-structure-dependent upconversion luminescence. Multifarious biological applications, including heterogeneous biodetection based on core-shell nanocrystals, homogeneous biodetection based on ultrasmall nanocrystals, superior nanothermometer based on hollow nanocrystals and in vivo bioimaging based on biodegradable nanocrystals, are briefly reviewed. Current challenges and future opportunities for lanthanide-doped inorganic nanocrystals for biological applications are also provided in the end.

Controllable crystal form transformation and luminescence properties of up-conversion luminescent material K3Sc0.5Lu0.5F6: Er3+, Yb3+ with cryolite structure.

In this paper, a novel cryolite-type up-conversion luminescent material K3Sc0.5Lu0.5F6: Er3+, Yb3+ with controllable crystal form was synthesized by a high temperature solid state method. K3Sc0.5Lu0.5F6: Er3+, Yb3+ can crystallize in monoclinic or cubic form at different temperatures. The composition, structure and up-conversion luminescence (UCL) properties of K3Sc0.5Lu0.5F6: Er3+, Yb3+ samples with different crystal form were investigated in detail. It is impressive that both monoclinic and cubic forms of K3Sc0.5Lu0.5F6: Er3+, Yb3+ show green emission (2H11/2/4S3/2→4I15/2). The luminescence intensity of cubic K3Sc0.5Lu0.5F6 is much higher than that of the monoclinic form, and the reasons are also discussed in detail. The results show that the luminescence intensity of up-conversion materials can be effectively tuned by controlling the crystal form. According to the power dependent UCL intensity, the UCL mechanism and electronic transition process were discussed. In addition, the fluorescence decay curves were characterized and the thermal coupling levels (TCLs) of Er3+ (2H11/2/4S3/2 → 4I15/2) in the range of 304–574 k were used to study the optical temperature sensing characteristics. All the results show that K3Sc0.5Lu0.5F6: Er3+, Yb3+ can be used in electronic components and have potential application value in temperature sensing fields.

Upconversion luminescence and ratiometric temperature sensing behavior of Er3+/Yb3+-codoped CaY2Ge3O10 germanate

A new series of CaY2–10xYb9xErxGe3O10 trigermanates (space group P21/c, Z = 4) has been synthesized using an EDTA-assisted method. Under 980 nm laser diode excitation, the samples exhibit intense upconversion luminescence corresponding to the characteristic transitions 2H9/2 → 4I15/2 (400–420 nm), 2H11/2,4S3/2 → 4I15/2 (500–600 nm) and 4F9/2 → 4I15/2 (625–725 nm) in Er3+ ions. The CaY1.5Yb0.45Er0.05Ge3O10 phosphor can be used as a good temperature sensor with high absolute and relative sensitivities Sa(max) = 0.0051 K−1 and Sr(max) = 0.0109 K−1.

Photochromic and temperature sensing properties of Ho3+-Yb3+ codoped Bi0.495-Na0.5TiO3 ceramics

Abstract With the development of modern industry and people's daily life, more and more smart materials with multifunction are required. In this study, multifunction material Bi0.495-xNa0.5TiO3:0.005Ho-xYb (x = 0.005, 0.010, 0.015, 0.020, 0.025, abbreviated as NBT:Ho-xYb) ceramics have been synthesized. The basic microstructure, upconversion luminescence, photochromic (PC) reaction, and temperature sensing properties of the ceramics have been systematically investigated. It is found that all the ceramics exhibit strong UC emissions, and the UC luminescence intensity depends on the Yb3+ doping content. An optimized UC emission is achieved at x = 0.015. Additionally, all the ceramics show an evident color change after 405-nm irradiation. Based on the PC reaction, a reversible UC luminescence modification can be achieved by alternating light irradiation (405 nm) and thermal stimulus at 230 °C, and the luminescence modulation is intensively dependent on the Yb3+ content and emission wavelength. Furthermore, the temperature sensing properties of NBT:Ho-0.015 Yb ceramics at low temperature have been investigated, illustrating a maximal sensitivity of 0.0029 K−1 at 93 K.

Bi3+-Doped BaYF5:Yb,Er Upconversion Nanoparticles with Enhanced Luminescence and Application Case for X-ray Computed Tomography Imaging.

In this work, BaYF5:20%Yb3+/2%Er3+/x%Bi3+ (abbreviated as BaYF5:Yb,Er,Bix, where x = 0-3.0) upconversion nanoparticles (UCNPs) with various doping concentrations of Bi3+ were synthesized through a simple hydrothermal method. The influence of the doping amount of Bi3+ on the microstructures and upconversion luminescence (UCL) properties of the BaYF5:Yb,Er,Bix UCNPs was studied in detail. The doping concentration of Bi3+ has little influence on the microstructures of the UCNPs but significantly impacts their UCL intensities. Under excitation of a 980 nm near-IR laser, the observed UCL intensities for the BaYF5:Yb,Er,Bix UCNPs display first an increasing trend and then a decreasing trend with an increase in the ratio x, giving a maximum at x = 2.5. A possible energy-transfer process and simplified energy levels of the BaYF5:Yb,Er,Bix UCNPs were proposed. The potential of the BaYF5:Yb,Er,Bix UCNPs as contrast agents for computerized tomography (CT) imaging was successfully demonstrated. An obvious accumulation of BaYF5:Yb,Er,Bix in tumor sites was achieved because of high passive targeting by the enhanced permeability and retention effect and relatively low uptake by a reticuloendothelial system such as liver and spleen. This work paves a new route for the design of luminescence-enhanced UNCPs as promising bioimaging agents for cancer theranostics.

A highly sensitive all-fiber temperature sensor based on the enhanced green upconversion luminescence in Lu2MoO6:Er3+/Yb3+ phosphors by co-doping Li+ ions

Great improvement of upconversion luminescence in Lu2MoO6:Er3+/Yb3+ phosphor is observed due to the introduction of Li+ ions and a highly sensitive all-fiber optical temperature measurement platform is established. X-ray diffraction (XRD) results show that pure Lu2MoO6:Er3+/Yb3+ phase has been prepared and Li2CO3 dramatically promotes the growth of Lu2MoO6:Er3+/Yb3+ phase in the scanning electron microscope(SEM) images. In comparison to the sample without Li+ ions, green upconversion luminescence intensity was increased by 516 times. The maximum absolute sensitivity of 0.015 K−1 is achieved at 423 K and temperature measurement error is ±0.8 K. The experimental results lay the foundation for the practical application of the ratiometric all-fiber optical temperature sensor.

Simultaneous tunable fluorescence lifetime and upconversion luminescence enhancement of NaLuF4:Er3+/Yb3+ microcrystals through heavily doped KF for multiplexing

A strategy is demonstrated for enhanced upconversion luminescence and significantly realized tunable fluorescence lifetime of NaLuF4 by simply doping KF. The upconversion luminescence intensities of the green and red are remarkably enhanced for molar ratio KF/Ln(Lu/Yb/Er) 80% doped NaLuF4 microcrystals compared to that without KF. Moreover, the fluorescence lifetime of NaLuF4 is tunable in a wide range depending on the doping molar ratio of KF. In a single 541 nm emission channel, 7 different fluorescence lifetimes ranging from 87.44μs to 285.47μs can be obtained. These superior performances are attributed to the tailored local environment. In addition, we use three of the materials to demonstrate multiplexing. Under 980 nm excitation, it displays the fake information “8”. However, scanning the security pattern in the time domain shows the real messages “1” and “9”.

A Plasmonic Platform for Upconversion Luminescence Enhancement

The approach to adapt upconversion nanoparticles to plasmonic structures has been studied to improve their inherent low quantum efficiency. However, the metal-based plasmonic structures have limits in extending their applications since they are rigid and opaque. In this study, we demonstrate a plasmonic film composed of an array of microbeads, which provides transferability and flexibility as well as distinctive upconversion luminescence enhancement. Our proposed structure comprises plasmonic silver nanoparticle-decorated silica microbeads on the dielectric-metal substrate, thereby providing remarkable improvements in absorption efficiency of near-infrared (NIR) light, and emission of visible (Vis) light via resonance mode excitation. As a result, the observed upconversion luminescence intensity exhibited three-order enhancement compared to reference under low power excitation. In addition, transparency and wide viewing angle property of emitted light for our film further extend its applicability for various fields such as absorption enhancement of photovotaics through visible light conversion in NIR and attachable NIR detection film.

An aptamer biosensor for CA125 quantification in human serum based on upconversion luminescence resonance energy transfer

CA125 is the most widely used biomarker for the early detection of ovarian cancer. Luminescence resonance energy transfer (LRET)-based probes show pronounced specificity and simplicity for CA125 detection, but they suffer from strong interference from autofluorescence of biosamples. To resolve this problem, near-infrared (NIR)-excitable upconversion nanoparticles (UCNPs) was employed as energy donor to fabricate CA125 biosensor. Carbon dots (CDs) were utilized as energy acceptor for the overlap between the upconversion luminescence (UCL) spectrum of UCNPs and the absorption spectrum of CDs. Aptamer-modified UCNPs were combined with CDs through π-π stacking interaction, which triggered the LRET process and induce UCL quenching with a high quenching efficiency of up to 90%. In presence of CA125, the formation of CA125-aptamer complex blocked the π-π stacking and recovered UCL. The UCL intensity increased linearly with the logarithm of CA125 concentration in the range from 0.01 to 100 U·mL−1. A detection limit of 9.0 × 10−3 U·mL−1 was obtained. This probe is also available for CA125 detection in human serum and may be a useful tool for the early detection of ovarian cancer.

Achieving high NIR-to-NIR conversion efficiency by optimization of Tm3+ content in Na(Gd,Yb)F4: Tm upconversion luminophores

Upconversion nanoparticles (UCPNs) capable of emitting near-infrared (NIR) light under NIR excitation attract much attention for bioapplications. However, the low upconversion efficiency and emission intensity significantly limits the progress in utilizing UCPNs. The present work is dedicated to the enhancement of upconversion efficiency and NIR luminescence intensity.The theoretical model that describes the changes in the populations of the excited states participating in the upconversion process was developed using a rate equations system for Yb3+–Tm3+ ions in hexagonal NaGdF4. According to the modeling results, by increasing of Yb3+ content to 80%, the intensity of NIR upconversion luminescence corresponding to 3H4–3H6 transition could be increased up to 3.5 times in comparison to 30:1.5 Yb–Tm concentration ratio which was calculated to be optimal and up to 9.5 times in comparison to often used 30:0.5 Yb–Tm concentration. The optimal doping content regions were determined. For 80% Yb3+ content the optimal Tm3+ content will be 2.5%, for 30% Yb3+ content—1.5%.Modeling results were confirmed experimentally by the synthesis of NaGdF4 nanoparticles doped with Yb3+ and Tm3+ with the concentration ratios of 80:2, 80:3, 80:4, and 80:5. To obtain single-phase hexagonal samples at high doping concentrations, higher synthesis temperatures were required. A single-phase sample NaGdF4: Yb3+–Tm3+ 80:5% was obtained at 320 °C synthesis temperature. According to the spectroscopic study of the obtained nanoparticles, the optimal concentration ratio for intense NIR luminescence obtaining was 80:3.The modeling results were in good agreement with the literature data and the results of our experiments. The developed model allows determining the optimal doping concentrations for obtaining effective NIR-to-NIR converters, based on NaGdF4:Yb3+–Tm3+ nanoparticles.

Gap‐Plasmon Coupled Nanopillar Array to Promote Upconversion Luminescence

This work theoretically explored the well-defined nanogap arranged as an upconversion (UC)/gold capping layer photonic nanopillar array on a back-reflecting film-coated Si substrate. The gap-plasmon (GP)-coupled periodic nanopillar array with encapsulating the upconversion layer (denoted as GPNA) is suggested to promote the upconversion luminescence (UCL) intensity at excitation and emission wavelengths. The optical localized-plasmon properties of the GPNA platform were probed by finite-difference time-domain (FDTD) method. With tweaking the geometric design parameters such as a cap thickness and gap distance, the GPNA platform can induce a prominent GP mode between the UC cap layer, thus leading to the significant plasmon-driven optical electromagnetic field amplification within the UC layer followed by substantial light absorption and UCL promotion. This proposed GP-coupled nanopillar array would pave the alternative way for a broad range of plasmon-sensitized applications which are able to absorb the incident excitation and resultant emission light.

A three-mode self-referenced optical thermometry based on up-conversion luminescence of Ca2MgWO6:Er3+,Yb3+ phosphors

To develop new up-conversion luminescent materials for optical thermometry, a sequence of Ca2MgWO6:xEr3+,yYb3+ phosphor samples were synthesized via high temperature solid-state reaction method. Their structure, morphology and luminescent performances were completely explored via X-ray diffraction, scanning electron microscopy and photoluminescence. Excited by 980 nm laser, all phosphor samples emit intense up-conversion luminescence of Er3+ at 531, 549 and 661 nm. Besides, these emissions were greatly enhanced with addition of Yb3+ ions. Benefiting from the different temperature dependence of three emission peaks, a dual-mode temperature sensor based on fluorescence intensity ratio (2H11/2/4S3/2 and 2H11/2/4F9/2) is realized by using single luminescent center. Meanwhile, the fluorescence lifetime of 4S3/2 state of Er3+ ions was used as the third temperature detection signal. More importantly, the phosphors exhibit superior thermal stability that will be helpful to obtain high precision temperature measurement. All results show that Ca2MgWO6:Er3+, Yb3+ samples could have potential applications for self-referenced optical thermometry.

Selective enrichment of Ln3+ (Ln = Yb; Er) and Cr3+ into SrF2 and ZnAl2O4 nanocrystals precipitated in fluorosilicate glass-ceramics: A dual mode optical temperature sensing study

The dual mode optical thermometry offers precise temperature sensing with self-calibration merit. To realise this, an oxy-fluoride precursor glass was transformed to a semi-transparent glass-ceramic having simultaneously precipitated SrF2:Yb3+/Er3+ and ZnAl2O4:Cr3+ phases. Under 980 nm excitation, intense green up-conversion (UC) luminescence of Er3+: 2H11/2, 4S3/2 → 4I15/2 and under 535 nm excitation, enhanced red down-conversion (DC) luminescence lifetime of Cr3+: 2E, 4T2 → 4A2 was realized. Both the UC and DC transitions were highly reliant upon temperature. The fluorescence intensity ratio (FIR) study of erbium's thermally coupled energy states (2H11/2 and 4S3/2) produced maximum temperature sensing sensitivity values of 1.11% K−1 at 334 K and 0.66% K−1 at 275 K, respectively. Likewise, temperature dependent luminescence lifetime of Cr3+ attributed to the transitions arising from the parity forbidden (2E → 4A2) and spin allowed (4T2 → 4A2) relaxations produced maximum temperature sensing sensitivity value equal to 0.19% K−1 at 435 K.

Triplet-triplet annihilation photon upconversion materials coated with TiO<sub>2</sub> nanocapsules

Triplet-triplet annihilation (TTA) upconversion is a technology that can convert low-energy light waves to high-energy light waves. The system is mainly composed of triplet sensitizers and energy receptors. The conversion mainly takes place in solution and is difficult to use as a whole molecule, which will greatly limit its application field. In this paper, by using the micelle soft template method to encapsulate the sensitizer and annihilant into the titanium dioxide shell, a highly efficient upconversion nanocapsule (TTA-UCNP) based on triplet-triplet annihilation upconversion was successfully prepared. In this study, BDP-I2 was used as the triplet sensitizer, perylene as the energy receptor, and soybean oil as the solvent. These newly synthesized nanocapsules can not only keep the up-conversion system in a solution environment, but also effectively block the quenching of triplet states by oxygen, and successfully achieve efficient upconversion luminescence in the aqueous phase. In the preparation process of the upconversion nanocapsules, we studied the effects of the type of surfactant, the amount of acid and the amount of butyl titanate on the upconversion luminescence intensity of the nanocapsules. The structure of nanocapsules was characterized by transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), and a highly efficient TTA upconversion luminescent material coated with titanium dioxide nanocapsules was successfully prepared.

Optical temperature sensor based on upconversion luminescence of Er3+ doped GdTaO4 phosphors

AbstractFor the development of optical temperature sensor, a series of GdTaO4 phosphors with various Er3+‐doping concentrations (0, 1, 5, 10, 25, 35, 50 mol%) were synthesized by a solid‐state reaction method. The monoclinic crystalline structure of the prepared samples was determined by X‐ray diffraction (XRD). Under excitations of 980 and 1550 nm lasers, the multi‐photon‐excited green and red upconversion (UC) luminescence emissions of Er3+ were studied, and the critical quenching concentration of Er3+‐doped GdTaO4 phosphor was derived to be 25 mol%. By changing the pump power of laser, it was found that the two‐photon and three‐photon population processes happened for the UC emissions of Er3+‐doped GdTaO4 phosphors excited by 980 and 1550 nm lasers, respectively. Furthermore, based on the change of thermo‐responsive green UC luminescence intensity corresponding to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ with temperature, the optical temperature sensing properties of Er3+‐doped GdTaO4 phosphor were investigated under excitations of 980 and 1550 nm lasers by using the fluorescence intensity ratio (FIR) technique. It was obtained that the maximum absolute sensitivity (SA) and relative sensitivity (SR) of Er3+‐doped GdTaO4 phosphors are as high as 0.0041 K−1 at 475 K and 0.0112 K−1 at 293 K, respectively. These significant results suggest that the Er3+‐doped GdTaO4 phosphors are a promising candidate for optical temperature sensor.

Insight into the Luminescence Alternation of Sub-30 nm Upconversion Nanoparticles with a Small NaHoF4 Core and Multi-Gd3+ /Yb3+ Coexisting Shells.

It is absolutely imperative for development of material science to adjust upconversion luminescence (UCL) properties of highly doped upconversion nanoparticles (UCNPs) with special optical properties and prominent application prospects. In this work, featuring NaHoF4 @NaYbF4 (Ho@Yb) structures, sub-30 nm core-multishell UCNPs are synthesized with a small NaHoF4 core and varied Gd3+ /Yb3+ coexisting shells. X-ray diffraction, transmission electron microscopy, UCL spectrum, UCL lifetime, and pump power dependence are adhibited for characterization. Compared with the former work, except for a smaller total size, tunable emission in color from red to yellow to green, and intensity from low to stronger than that of traditional UCNPs is achieved for ≈10 nm NaHoF4 core size by means of changing number of layers and Gd3+ /Yb3+ concentration ratios in different layers. Besides, simultaneously doping Ho3+ into the shells will result in lowered UCL intensity and lifted green/red ratio. Surface energy loss and sensitizing energy supply, which can be modulated with inert shielding of Gd3+ and sensitization of Yb3+ , are proved to be the essential determinant. More UCL properties of these peculiar Ho@Yb UCNPs are uncovered and detailedly summarized, and the findings can help to expand the application scope of NaHoF4 into photoinduced therapy.

Manipulation of upconversion property and enhancement of sensitivity by tailoring the local structure

AbstractTailoring the local crystal environment around the activators is one of an important way to enhance the upconversion (UC) luminescence intensity. Herein, we substitute the Y3+ lattice with La3+ ion gradually in Y2Ti2O7:Yb3+, Er3+ phosphor and investigate the effect of La3+ concentration on the UC luminescent properties as well as the temperature sensing behaviors. During the phase transformation process from cubic Y2Ti2O7 to monoclinic La2Ti2O7, the La3+ ions also play an important role on the adjustment of size and morphology of particles. Furthermore, the cooperation of La3+ ion is in favor of the crystal growth toward the easy growth directions. The UC luminescence intensities can be enhanced efficiently with the increasing of La3+ concentration. The sensitivity for temperature sensing can be improved by the increasing of La3+ concentration in the Y2Ti2O7 and La2Ti2O7 two‐phase coexistence system and the maximum SA is 45.3 × 10−4 K−1 at 410K when the La3+ concentration is 80%. The maximum SA and corresponding temperature can be adjusted by controlling the La3+ concentration, which means that (Y0.94‐xLax)2Ti2O7: Er3+/Yb3+ phosphors may be applicable to different working environment.