Upconversion Fluorescence Research Articles

A smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor for visual detection of mercury ions and l-penicillamine

Establishment of a rapid, sensitive, visual, accurate and low-cost fluorescence detection system to detect multiple targets was of great significance in food safety evaluation, ecological environment monitoring and human health monitoring. In this work, a smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor was proposed based on metal-organic framework (NH2-MIL-101(Fe)) and CdTe quantum dots (CdTe QDs) for visual detection of mercury ions (Hg2+) and L-penicillamine (L-PA), in which NH2-MIL-101(Fe) was used as the reference signal and CdTe QDs was used as the response signal. The down-conversion fluorescence system at excitation wavelength of 300 nm (ex: 330 nm) was used to detect Hg2+ and L-PA, in which the detection limit of Hg2+ was 0.053 nM with the fluorescence color changed from green to blue, and the detection limit of L-PA was 1.10 nM with the fluorescence color changed from blue to green. Meanwhile, the up-conversion fluorescence system at excitation wavelength of 700 nm (ex: 700 nm) was used to detect Hg2+ and L-PA. The detection limits of Hg2+ and L-PA were 0.11 nM and 2.93 nM, respectively. The detection of Hg2+ and L-PA were also carried out based on the color extraction RGB values identified by the smartphone with a detection limit of 0.091 nM for Hg2+ and 8.97 nM for L-PA. In addition, the concentrations of Hg2+ and L-PA were evaluated by three-dimensional dynamic analysis in complex environments. The smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor system provides a new strategy for detection Hg2+ and L-PA in food safety evaluation, environmental monitoring and human health monitoring.

Ultrafast excited state dynamics of pyridine N-oxide derivative in solution; femtosecond fluorescence up-conversion and theoretical calculations

In this study we have investigated 2-ethylamino-4-nitro-6-methyl pyridine N-oxide (2E6M) molecule that belongs to important group of Proton Coupled Electron Transfer (PCET) compounds where both the charge transfer (CT) and proton transfer processes in excited states may proceed. In this case, this is possible due to the donors and acceptors of electrons and protons in this system, as well as due to the presence of intramolecular {N-H… O [2,566(3) Å}, hydrogen bond.Using stationary and time-resolved spectroscopy, as well as quantum chemical calculations on the DFT and TD DFT B3LYP/6-31G (d,p) level of theory, a partial CT nature of the S0 → S1 transition in both tautomeric forms (N and T) has been revealed. Additionally, the excited state intramolecular proton transfer (ESIPT) process shown to be more favorable in apolar and weakly polar solvents than in strongly polar acetonitrile (EN(S1) > ET(S1). The displacement of charge from the amine group and the ring to the nitro group has been observed on the changing shapes of the HOMO and LUMO orbitals involved in this transition what further quantitatively allowed to realize the increase in the dipole moment of both forms in the electronic excited state. The calculations show that in two solvents with radically different polarity (heptane, acetonitrile), dipole moments of both forms are very similar [in acetonitrile uN(S1) and uT(S1) are 11.0 D and 11.5 D, respectively]. Hence, in polar media both forms can be stabilized in a comparable manner. This made it difficult for us to assign a single fluorescent band in acetonitrile to one of the tautomeric forms. However, it seems that due to application of time-resolved spectroscopy, this problem has been clarified. The TCSPC decay curve in acetonitrile with an ultrafast lifetime assigned to the (N) form, along with the femtosecond up-conversion signals that demonstrated only an ultrafast decay without any rise-time of a new excited (T) species, allowed us to conclude that in 2E6M in strongly polar solvent the ESIPT does not occur.The unique fluorescence band origins from the (N) form. In protic solvents, the significant kinetic isotopic effects have provided us with conclusive evidence for the presence of the solvent-assisted ESIPT process. Furthermore, it was noticed that the fluorescence lifetime in D2O (100–120 fs) estimated from the up-conversion signals is about 40 times shorter relative to methanol. This may suggest that the sine qua non for the ESIPT process in 2E6M in protic solvents is the formation of a complex with a solvent molecule in the hydrogen bridge between the proton donor and proton acceptor, respectively.

A Compact Fluorescent Probe for Real-Time Thermal Monitoring of Chips

In this paper, a compact fluorescent probe based on fluorescence intensity ratio (FIR) technique is proposed for real-time thermal monitoring of chips, the sensing unit of which is based on a self-made tellurite optical fiber (TOF) co-doped with Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> /Yb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions. Temperature information was demodulated by analyzing the up-conversion fluorescence emission spectra generated using a 980 nm laser pump. Experimentally characterized the relationship between the FIR related to two thermally coupled energy levels and the ambient temperature, and on-line investigated the temperature change of Central Processing Unit (CPU) and North Bridge Chip for about 80 min during the cycle startup/shutdown process. The proposed probe exhibits a fast time response of about 1.1 s in a step temperature-varying environment and a small absolute error of <0.85 K in the real-time thermal monitoring of the CPU. To the best of our knowledge, this is the first report on fluorescent probes for thermal detection of chips. The proposed probe has the characteristics of anti-electromagnetic interference, explosion-proof, corrosion resistance, and can effectively avoid cross-sensitivity problems caused by environmental parameters. It provides a novel and reliable method for real-time thermal monitoring of chips.

Luminescence and temperature sensing properties of KLu(MoO4)2:Ln3+ phosphors

A series of phosphors based on KLu(MoO4)2 are synthesized by the citric acid assisted hydrothermal method combined with subsequent calcination in this paper. By doping Yb3+/Er3+, Yb3+/Ho3+ and Yb3+/Tm3+ into KLu(MoO4)2 host, the green, red and blue emissions are realized, respectively. Moreover, the amount of Yb3+/Er3+ doping can affect the fluorescence upconversion emission intensity. The temperature sensing property of KLu(MoO4)2: 20%Yb3+,0.8%Er3+ is explored in the range of 323–573 K. In the heating process, the maximum absolute sensitivity is 0.01187 K−1 at 498 K. In addition, by constructing the cycle process of heating and cooling, the maximum sensitivity relative deviation of the two processes is only −0.72%, which means the KLu(MoO4)2:Yb3+/Er3+ phosphor has excellent stability in temperature measurement. Our research demonstrates that the KLu(MoO4)2:Ln3+ phosphors have potential application prospects in the fields of temperature sensor and multicolor fluorescence.

Effect of annealing temperature on optical properties of Erbium doped Y2Zr2O7 transparent ceramics

Through the vacuum sintering method, Erbium-doped Y2Zr2O7 transparent ceramics were successfully fabricated. The obtained ceramics were annealed at different temperatures and the relationship between annealing temperature and sample structure was investigated to reveal the effect of oxygen vacancy. Y1.98Er0.02Zr2O7 ceramics annealed at 800 °C starts to be transparent and when added up to 900 °C, samples show the highest transmittance over 76% in the near-infrared (NIR) region. Then the transmittance gradually decreased to 71% with the increase of annealing temperature. XRD and SEM measurements were performed to characterize the crystal structure and microstructure of Er3+: Y2Zr2O7 as-prepared powders and ceramics. The excitation spectra display that Y1.98Er0.02Zr2O7 ceramics can be effectively excited by 382 nm. When the annealing temperature exceeds 700 °C, two strong green emission bands and one red emission band can be observed in both up-conversion (UC) and down-conversion (DC) fluorescence spectra. Our results suggest that annealing temperature has a great impact on the structure and optical properties of Er3+: Y2Zr2O7 ceramics, which is significant for fabricating ceramics with better optical properties.

Fluorescence temperature sensing of NaYF4:Yb3+/Tm3+@NaGdF4:Nd3+/Yb3+ nanoparticles at low and high temperatures

NaYF4:Yb3+/Tm3+@NaGdF4:Nd3+/Yb3+ upconversion nanoparticles were prepared using a solvothermal method, and the effects of key factors such as the content of sensitiser Nd3+ and Yb3+ on their luminescence properties were investigated. The nanoparticles are homogeneous in size and well dispersed. Under 808 nm excitation, it can produce strong upconversion fluorescence. At the same time, the nanoparticles have good temperature sensing properties at the thermally coupled energy levels of 700 and 646 nm for Tm3+. Using its fluorescence intensity ratio, accurate temperature measurements can be performed, and it has been found that it exhibits different temperature sensing properties in low and high-temperature regions. The maximum relative sensitivity was found to be 0.88% K−1 and 1.89% K−1 for the low-temperature region of 285–345 K and the high-temperature region of 345–495 K. The nanoparticles were applied to the internal temperature measurement of lithium batteries and the actual high-temperature environment, respectively, and were found to have good temperature measurement performance.

Extraordinary upconversion enhancement in hybrid metasurface by simultaneous excitation/emission band match

Lanthanide doped upconversion nanoparticles (UCNPs) suffers a significant challenge of low quantum efficiency, which seriously limited their applications in photovoltaic device and bioimaging. In this work, we proposed a plasmonic pattern/UCNPs/metal film hybrid metasurface with ultrahigh upconversion enhancement factor. The plasmonic absorption bands can be precisely controlled to simultaneously match both the excitation and the emission wavelength of UCNPs. By constructing the efficient coupling between the local field and the UCNPs, the upconversion fluorescence can be enhanced by 4–6 orders of magnitude. It’s worth noting that such strategy almost covered the two major types of lanthanide doped UCNPs, which were sensitized by Yb3+ (excited under 980 nm) and Nd3+ (excited under 808 nm). The emission enhancement factor was found to be sensitive to the structural parameters and refractive index of the surroundings. Based on this effect, an upconversion intensity and spectra shift dual-mode sensing to environment refractive index can also be achieved. The proposed hybrid metasurface provided an effective way to achieve highly efficient upconversion emission, and the results can also be helpful in solar cells and biological detection.

Excitation energy mediated cross-relaxation for tunable upconversion luminescence from a single lanthanide ion

Precise control of energy migration between sensitizer ions and activator ions in lanthanide-doped upconversion nanoparticles (UCNPs) nowadays has been extensively investigated to achieve efficient photon upconversion. However, these UCNPs generally emit blue, green or red light only under fixed excitation conditions. In this work, regulation of the photon transition process between different energy levels of a single activator ion to obtain tunable upconversion fluorescence under different excitation conditions is achieved by introducing a modulator ion. The cross-relaxation process between modulator ion and activator ion can be controlled to generate tunable luminescence from the same lanthanide activator ion under excitation at different wavelengths or with different laser power density and pulse frequency. This strategy has been tested and proven effective in two different nanocrystal systems and its usefulness has been demonstrated for high-level optical encryption.

Excitation wavelength dependent photoluminescence and photochromic studies of Yb3+/Er3+ doped β−KYF4 and β−NaYF4 nanoparticles

We report both resonant and off-resonant laser excitation of Er3+ upconversion fluorescence and colour tunability in Er3+/Yb3+ co-doped KYF4 and NaYF4 nanoparticles. The nanoparticles were prepared using a hydrothermal method with particle sizes of 74 ± 20 nm and 345 ± 91 nm for β−KYF4 and β−NaYF4, respectively. The Yb3+ 2F7/2 → 2F5/2 absorption spectra exhibit absorption maxima at 10237 cm−1 (977 nm) for β−NaYF4 and 10267 cm−1 (974 nm) for β−KYF4 nanoparticles. The Er3+ upconversion fluorescence spectra consist of the 2H11/2,4S3/2, and 4F9/2 → 4I15/2 transitions for either 974, 977 or 980 nm laser excitation in both materials. We observed an enhancement in the upconversion intensity by a factor of up to 20 for β−KYF4 and 1.5 fold for β−NaYF4 under resonant excitation compared with off-resonant excitation at 980 nm. Tuneable upconversion fluorescence wavelength was achieved in β−KYF4:Yb/Er nanoparticles by adjusting the excitation wavelength. The CIE chromaticity coordinates are (0.6836, 0.3151) with a highest red colour purity of 99.70% for β−KYF4 (4700 K) and (0.3953, 0.5915) with a colour purity of 96.84% for β−NaYF4 (4533 K) nanoparticles. The respective absolute upconversion quantum yields are 1.18% and 2.34% under low power density (1.65 W⋅cm−2).

Unraveling the binding interaction between polyvinyl chloride microplastics and bovine hemoglobin: Multi-spectroscopic studies

In this paper, the interaction between polyvinyl chloride microplastics (PVC MPs) and bovine hemoglobin (BHb), a carrier of oxygen in the blood circulation system, has been investigated by multi-spectroscopic techniques. The UV-vis absorption and steady state fluorescence spectroscopy prove that BHb molecules can be bound to the surface of PVC MPs by their electrostatic force interaction, and the up-conversion fluorescence measurements confirm that the lifetimes of BHb remain unperturbed in this process. Circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy further demonstrate that the BHb-PVC MPs binding has clearly changed the secondary structures of BHb. Moreover, the interactions between PVC MPs with different sizes (0.5, 1 and 2 µm) and BHb have been studied and compared, indicating that the binding affinity decreased with the increasement of particle size of PVC MPs. Those results have implied that microplastics could enter the human blood circulatory system and organs, and might be potentially toxic to the human body.

Full relaxation dynamics recovery from ultrafast fluorescence experiments by means of the stochastic model: Does the solvent response dynamics depend on the fluorophore nature?

• The model of non-stationary charge-transfer dye fluorescence spectrum is presented. • The solvation dynamics depend on fluorophore. • The contribution of intramolecular vibrations in FLUPS is separated. • The solvent relaxation function of hexane is determined. An approach to analysing time-resolved fluorescence spectra has been developed for dyes with non-parabolic free energy curves of the excited and ground states. It incorporates the description of the solvent relaxation and redistribution/relaxation of intramolecular high-frequency vibrations proceeding in parallel with the pumping. The approach has been applied to simulate spectra of covalently linked perylene-dimethylaniline (PD) in a series of solvents of different polarity. The developed approach combined with the achieved temporal resolution of the modern fluorescence upconversion spectroscopy is shown to provide a possibility to disentangle the relaxation of high-frequency vibrations and the dynamics of the solvent. In this compound the reorganization of both intramolecular vibrations and the solvent strongly affects the absorption and fluorescence spectra so that their influence on spectral dynamics is highly entangled. The comparison of fluorescence spectral dynamics of two dyes, coumarin 153 and PD, shows that the solvation dynamics depend on the fluorophore. The fitting of simulated fluorescence spectral dynamics of PD to the experimental data enables us to determine the solvent relaxation function of hexane.

Surface Plasmon Enhanced Upconversion Fluorescence in Short-Wave Infrared for In Vivo Imaging of Ovarian Cancer.

Short-wave infrared (SWIR; 850-1700 nm) upconversion fluorescence enables "autofluorescence-free" imaging with minimal tissue scattering, yet it is rarely explored due to the lack of strongly emissive SWIR upconversion fluorophores. In this work, we apply SWIR upconversion fluorescence for in vivo imaging with exceptional image contrast. Gold nanorods (AuNRs) are used to enhance the SWIR upconversion emission of small organic dyes, forming a AuNR-dye nanocomposite (NC). A maximal enhancement factor of ∼1320, contributed by both excitation and radiative decay rate enhancement, is achieved by varying the dye-to-AuNR ratio. In addition, the upconversion emission intensity of both free dyes and AuNR-dye NCs depends linearly on the excitation power, indicating that the upconversion emission mechanism remains unchanged upon enhancement, and it involves one-photon absorption. Moreover, the SWIR upconversion emission shows a significantly higher signal contrast than downconversion emission in the same emission window in a nonscattering medium. Finally, we apply the surface plasmon enhanced SWIR upconversion fluorescence for in vivo imaging of ovarian cancer, demonstrating high image contrast and low required dosage due to the suppressed autofluorescence.

Enhanced dual-wavelength up-conversion luminescence and temperature sensitivity of NaYF4:Yb3+, Er3+ phosphors by Bi3+ introducing

The up-conversion composite fluoride phosphor BixNayYzF3x + y+3z +3z+3m+3n: Er3+m, Yb3+n were synthesized using the optimized low-temperature combustion synthesis (LCS) method. The optimal formula was determined by step-by-step orthogonal experiments. The effects of the introduction of Bi3+ ions on phase formation and fluorescence intensity were systematically studied. The results indicate that introducing 10 mol% Bi3+ ions can substantially strengthen the dual-wavelength up-conversion fluorescence intensity of the sample. Then the temperature sensitivity of the sample is calculated, indicating that the sample has good temperature sensitivity and can be used as an effective material for temperature sensors. X-ray diffraction and scanning electron microscopy (SEM) were used to analyze the phase composition and morphology of the phosphor. The product exhibits characteristic emission of Er3+ ions under the excitation of 1550 nm ＆ 980 nm dual-wavelength, and its luminescence mechanism was studied. This work provides new ideas for studying photothermal dual response up-conversion fluoride phosphors under excitation at 1550 nm & 980 nm.

Up-conversion luminescence and temperature sensing properties based on Y2GeO5: Er3+, Yb3+ phosphors for three-mode optical thermometry

Herein, a series of novel Y2GeO5: Er3+, Yb3+ phosphors were prepared through traditional high-temperature solid-state reactions under an air atmosphere. During whole experiments, the fluorescence intensity ratio (FIR), crystal structure, up-conversion (UC) luminescence, and energy transmission between Er3+ and Yb3+ of all the samples were combined to explore their properties as optical thermometer. By exciting 980 nm laser, strong UC luminescence of Er3+ ions was emitted at 522, 546, and 652 nm, and by increasing the Er3+, Yb3+ ions co-doped concentration, the UC luminescence intensity of Er3+ ions was greatly enhanced. By using two different techniques, a dual-mode temperature sensor was explored based on the FIR of thermal coupling (2H11/2/4S3/2) and non-thermal coupling (2H11/2/4F9/2) energy levels. And the maximal relative sensitivities of thermal coupling and non-thermal coupling were 1.17%·K−1 and 1.71%·K−1, respectively. In addition, the fluorescence lifetime was used as the third temperature detection signal. And the maximum of relative sensitivity based on fluorescence lifetime was 1.81%·K−1. All the above research shows that Y2GeO5: Er3+, Yb3+ phosphors are prospective applications in temperature sensing.

Temperature distribution measurement inside an Er:Yb:Lu2Si2O7 crystal under 1.55 μm laser operation

Based on the fluorescence intensity ratio technique, the temperature distribution inside an Er:Yb:Lu2Si2O7 crystal was measured in real time when a 1.55 μm laser was operating. The polarized green up-conversion fluorescence in 500–580 nm of the crystal generated simultaneously under laser operation was used as the temperature probe. At a pump beam waist diameter of 400 μm, the highest temperature inside the crystal reached 507 K when the incident pump power and output mirror transmission were 11.13 W and 1.3%, respectively. The experimental result was compared with the theoretical temperature distribution inside the crystal simulated by the finite element analysis method, and the difference between them was analyzed.

(Invited) Dynamics of Porphyrin-Fullerene Charge Transfer and Recombination Via Ultrafast Spectroscopy

Electron donor-acceptor (D-A) interactions have been the subject of intense scrutiny by the scientific community due to their role in a variety of applications, such as solar energy production, photocatalysis, and stimulus-responsive materials. We chose porphyrins and fullerenes for our fundamental studies of D-A interactions, as they are the prototypical D-A pair by virtue of their well-positioned energy levels, low reorganization energies, and the high extinction coefficients of the porphyrin ring in the visible region. Moreover, they give us the opportunity to not only choose between different bound or endohedral metal ions or clusters, but also to connect them in different ways in order to tune their behavior. We have used time-resolved spectroscopic techniques, including transient absorption, fluorescence upconversion, and time-correlated single-photon counting, to untangle charge separation and recombination dynamics upon donor excitation in the femto- to nanosecond regime to gain additional insight into the relationship between structure and behavior.

High-PLQY and Efficient Upconverted Fluorescence of the TAPC/PBD Exciplex with Fluorescent Guests

High-PLQY and Efficient Upconverted Fluorescence of the TAPC/PBD Exciplex with Fluorescent Guests

The sensitization and deactivation effects of Nd3+ ion in Nd,Ho:CaYAlO4 disordered crystal for 2.86 µm tunable and ultrafast laser

Nd,Ho:CaYAlO4 (Nd,Ho:CYA) crystals with two different Nd3+ doping concentrations for ∼3 µm mid-infrared (MIR) laser were grown successfully by the Czochralski method. The sensitization and deactivation effects of Nd3+ ions were analyzed based on the polarized absorption spectra, mid-infrared and upconversion fluorescence spectra and fluorescence decay curves in detail. Excited by 808 nm laser diode (LD), strong 2.86 µm emission was observed. The maximum emission cross section was calculated to be 1.93 × 10-20 cm2 in 1.0 at.% Nd, 2.5 at.% Ho:CYA, and the FWHM was about 115 nm. The ∼3 µm emission was enhanced by 10 times compared to the 2.5 at.% Nd, 2.5 at.% Ho:CYA crystal. Due to the dual function of Nd3+ as effective sensitizing and deactivating ion, 1.0 at.% Nd, 2.5 at.% Ho:CYA had a relatively longer lifetime 0.240 ms for the upper level 5I6, while the lifetime of the lower level 5I7 reduced to 0.723 ms, which was greatly advantageous to the population inversion. The calculated deactivation efficiency from Ho3+: 5I7 to Nd3+: 4F13/2 was estimated to be 89.66%. All results indicated that 1.0 at.% Nd, 2.5 at.% Ho:CYA crystal is a promising gain medium for ∼3 µm tunable and ultrafast laser output under 808 nm LD pump.

Targeted Immunoimaging of Tumor-Associated Macrophages in Orthotopic Glioblastoma by the NIR-IIb Nanoprobes.

Developing dynamic and highly sensitive methods for imaging M2-type tumor-associated macrophages (TAMs) is vital for monitoring the tumor progression and assessing the therapeutic efficacy. Here, the fabrication and application of rationally designed Er-based rare-earth nanoprobes for the targeted imaging of M2-type TAMs in glioblastoma (GBM) through the second near-infrared (NIR-II) fluorescence beyond 1500nm is reported. The NIR-IIb fluorescence of Er-based rare-earth nanoparticles can be remarkably enhanced by optimizing their core-shell structures and the shell thickness, which allows for in vivo imaging under excitation by a 980nm laser with the lowest power density (40mW cm-2 ). These bright Er-based nanoparticles functionalized with M2pep polypeptide show notable targeting ability to M2-type macrophages, which has been well tested in both in vitro and in vivo experiments by their up-conversion (UC) fluorescence (540nm) and down-shifting (DS) fluorescence (1525nm), respectively. The targeting capability of these nanoprobes in vivo is also demonstrated by the overlap of immunofluorescence of M2-type TAMs and Arsenazo III staining of rare-earth ions in tumor tissue. It is envisioned that these nanoprobes can serve as a companion diagnostic tool to dynamically assess the progression and prognosis of GBM.

Inorganic photochromism material SrHfO3:Er3+ integrating multiple optical behaviors for multimodal anti-counterfeiting

Photochromic materials usually have different physical and chemical properties when they are in different states. Inorganic photochromic materials are widely used in the fields of information storage, optical switches and sensors due to their long lifetime, good thermal stability and fatigue resistance. However, the current inorganic photochromic materials, possessing a unitary optical property, cannot fulfill the requirement of multimodal high-level security anti-counterfeiting. In this work, we report the multiple optical behaviors integrated inorganic photochromic Er3+-doped strontium hafnate ceramics. It integrates multiple optical functions, including photochromism, downshifting photoluminescence, up-conversion luminescence, afterglow, and thermoluminescence. The fluorescence modulation contrast (FMC) maximum of SrHfO3: Er3+ can achieve as high as to 77.21% in the mode of photochromism-driven the quenching of downshifting photoluminescence. The FMC maximum can approach 70.24% in the mode of photochromism-driven the quenching of up-conversion luminescence. By alternating the light stimulation and thermal field effect, both photochromism and fluorescence modulation exhibit excellent stability and robust fatigue resistance. The mechanisms of the observed photochromism, downshifting and up-conversion luminescence, fluorescence modulation, afterglow, and thermoluminescence were studied systematically. The combination of the multiple optical behaviors functionalizes the as-obtained material for versatile applications. As a proof of concept, a flexible film was designed and prepared, demonstrating the practical application of SrHfO3: Er3+ material for multimodal high-level security anti-counterfeiting.