Fluorescence Intensity Ratio Research Articles

Cooperative-luminescence-assisted single-band upconverted red emission in Er3+ and Yb3+ co-doped MgAlON transparent ceramic

Although single-band emission upconversion fluorescence, which is particularly important in sensors, biomedical and imaging applications, has been extensively investigated in nanoparticles using energy transfer engineering, it is still difficult to be achieved in transparent ceramics. Herein, the MgAlON: Er3+/Yb3+ transparent ceramics with functionalized grain boundaries were successfully fabricated. Lanthanide ions were investigated to highly enrich at the MgAlON grain boundaries, resulting in novel fluorescent properties. Upon 980 nm laser excitation, the sample emitted temperature and excitation power-independent single-band red upconverted fluorescence with a red-to-green fluorescence intensity ratio of ∼25. The new mechanism of Yb3+-Yb3+ cooperative fluorescence-assisted energy transfer, which is responsible for the single-band feature, was elucidated. Moreover, the upconverted fluorescence chromaticity can be modified by the excitation wavelength, relying on the existence of the cooperative fluorescence level and its related energy transfer mechanism. This work reveals the potential of grain boundary functionalization of transparent ceramics in energy transfer engineering.

Ratiometric and sensitivity detection of AChE: Silicon nanomaterial-triggered aggregation-induced emission of copper nanoclusters

As an important kind of hydrolase, acetylcholinesterase (AChE) is closely related to many neurological diseases. Therefore, the development of reliable and sensitive methods for the determination of its activity is of great research significance. In this work, silicon nanomaterials (SiNPs) with positive charge and glutathione-modified copper nanoclusters (CuNCs) with negative charge were designed to establish a ratiometric fluorescence system (SiNPs@CuNCs) based aggregation-induced emission (AIE) strategy. The SiNPs@CuNCs could directly detect the AChE activity without any intermediate quencher. Acetylthiocholine iodide could be catalyzed and hydrolyzed into thiocholine (TCh) by AChE. TCh could effectively quench the fluorescence intensity (FI) of CuNCs in SiNPs@CuNCS, yet the FI of SiNPs was unchanged. The activity of AChE was measured by FI ratio (FCuNCs/FSiNPs). The linear range of SiNPs@CuNCs for the quantitative detection of AChE was 0–0.05 U/mL, and the limit of detection was 0.003 U/mL. SiNPs@CuNCs successfully realized the trace detection of AChE activity in a real serum sample, and satisfactory results were obtained. This research will provide unique insights into the development of new ratiometric fluorescent nanomaterials for the determination of other hydrolase.

Tm3+-doped Cs2Ag0.6Na0.4In0.9Bi0.1Cl6 microcrystals for thermometry

Lead-free double perovskites have superb luminescence properties for broad applications. However, increasing or improving near-infrared (NIR) photoluminescence (PL) is still a challenge. In this paper, a high-performance microcrystal is designed based on Tm3+ heavily doped Cs2Ag0.6Na0.4In0.9Bi0.1Cl6 (CANIBC), which realize both the self-trapped excitons (STEs) and Tm3+ NIR emission. The emission mechanism and energy transfer (ET) process are studied by steady-state and time-resolved PL spectra. The ET efficiency from STEs to Tm3+ can reach 38.3 %, and the NIR PL quantum yield of Tm3+ can reach 22.7 %. Meanwhile, the PL spectra of Tm3+-doped CANIBC microcrystals (MCs) with different concentrations are used to investigate their temperature sensing properties based on both fluorescence intensity ratio (FIR) and lifetime. Based on the FIR, relative sensitivity (Sr) can reach 2.93 % K−1 at 303 K. Moreover, based on lifetimes, Sr can maintain more than 1.55 % K−1 from 303 to 453 K, and maximum Sr can also achieve 2.38 % K−1 at 360 K. These excellent luminescence and sensing properties offer greater development potential in the field of NIR phosphor and thermometry.

Reengineering the thermometric behaviors of Er3+/Yb3+-codoped Gd2Mo3O12 microparticles via dual-mode luminescence manipulation

Series of Er3+/Yb3+-codoped Gd2Mo3O12 (GMO:Er3+/2xYb3+) microparticles with dual-mode luminescence were fabricated with the assistance of sol-gel method. The phase structure, morphological information, upconversion (UC) and down-shifting luminescence properties of the final products were systematically investigated. At 980 nm light irradiation, strong UC emissions rise in all the products and their intensities depend on the dopant concentration, where the optimum status occurs at x = 0.25 and the two-photon capture procedure results in the UC emission mechanism. Besides, excited at 378 nm, the down-shifting photoluminescence is also gained in resulting samples. By means of the fluorescence intensity ratio technique, the thermometric properties of the studied samples were investigated through analyzing the diverse thermal quenching features of the green emissions from thermally coupled levels of Er3+. When the UC emission is selected, the maximum absolute and relative sensitivities of the GMO:Er3+/2xYb3+ microparticles are 0.0076 and 1.15% K−1, respectively, whereas they shift to 0.0036 and 0.89% K−1, respectively, when the down-shifting photoluminescence is adopted. Note that, the sensor sensitivities of developed microparticles are related to the luminescence mode, while they do not depend on Yb3+ content. These results suggest that the GMO:Er3+/2xYb3+ microparticles are promising thermosensitive luminescent materials for optical thermometry and their thermometric features can be tuned through changing luminescence mode.

A porphyrin-based metal-organic framework Al-TCPP for highly selective sensing of copper ions with exceptional low limit of detection

Sensitive and selective detection of copper ions (Cu2+) using fluorometric methods is of growing significance due to their widespread industrial use, which poses severe environmental and health risks. Here, we reported a porphyrin-based luminescent metal-organic framework (labelling LMOF), Al-TCPP, which exhibits dual emission peaks at 467 and 646 nm upon excitation by a single wavelength. When exposed to Cu2+ ions, the fluorescence peak at 646 nm reduces while the intensity of the 467 nm remains steady. This intriguing property enables the construction of a ratio-metric fluorescence sensor that utilizes an internal standard, significantly enhancing Cu2+ sensing accuracy. Our study establishes a linear relationship (y = 0.0454x + 0.3081) between the fluorescence intensity ratio I467/I646 and the Cu2+ concentration, with a high correlation coefficient R2 = 0.9943. Impressively, the present Al-TCPP achieves a low limit of detection (LOD) of 5.28 nM, one of the lowest reported values for Cu2+ detection. The mechanism underlying this phenomenon involves charge transfer from TCPP ligands in Al-TCPP to Cu2+ ions, as revealed by solid-state NMR and X-ray photoelectron spectroscopy analysis. Utilizing Al-TCPP, we successfully developed test strips for the practical Cu2+ detection. Furthermore, the present Al-TCPP has also effectively applied to determine low Cu2+ content in various samples, including water, tea and serum. This study demonstrates the versatility and practical applicability of present Al-TCPP LMOF for selective detection of Cu2+ ions in diverse environments.

A Dual-mode Ratiometric Fluorometric and Colorimetric Platform Based on Nitrogen-doped Carbon Dots and o-phenylenediamine for the Detection of Nitrite.

In this study, a dual-mode ratiometric fluorometric and colorimetric platform for the determination of nitrite in pickles was proposed by exquisitely employing the fact that non-fluorescent o-Phenylenediamine (OPD) was oxidized by nitrite under acidic conditions to form fluorescent 2,3-diaminophenazine (DAP) (Em = 575), which meanwhile quench the fluorescent nitrogen-doped carbon dots (N-CDs) at 455nm, the ratio of fluorescence intensity of DAP to N-CDs (F575/F455) changed with the increase of nitrite accompanied by visible color changes. Thus, nitrite can be quantitatively detected within a wide linear range (10-500 µM) with a low detection limit of 0.45 µM due to the high quantum yield of 39.7% of N-CDs. In addition, the colour of the N-CDs/OPD system changed from transparent to yellow when the nitrite was introduced, enabling colorimetric and on-site visual detection. The detection limit of the colorimetric method was 3.03 µM with a linear range of 10-500 µM. The proposed ratiometric fluorometric method has pleasant selectivity and good immunity to interference.

Three-mode fluorescence thermometers based on double perovskite Ba2GdNbO6:Eu3+,Mn4+ phosphors

Herein, Ba2GdNbO6:Eu3+,Mn4+ phosphors with dual emission centers were manufactured as three-mode fluorescence thermometers. Their structure, micromorphology and luminescent properties were explained in-depth. Excited at 394 nm, the characteristic emission peaks of transitions of 5D0→7F of Eu3+ and 2Eg→4A2g of Mn4+ in Ba2GdNbO6:Eu3+,Mn4+ can be simultaneously detected. In addition, three-mode fluorescence thermometers with high sensitivity were developed, utilizing temperatures dependence of emission intensity (EI) of Mn4+, fluorescence intensity ratio (FIR) of Eu3+ and Mn4+, as well as fluorescence lifetime (FL) of 2Eg level of Mn4+. In EI, FIR and FL modes, the maximal relative sensitivities achieve 1.78 %K−1@423 K, 2.72 %K−1@483 K and 1.73 %K−1@430 K, respectively. The results indicate that Ba2GdNbO6:Eu3+,Mn4+ can be used as a candidate material for three-mode fluorescence thermometers.

Pure-green upconversion emission and high-sensitivity optical thermometry of Er3+-doped stoichiometric NaYb(MoO4)2

The optical temperature sensor based on fluorescence intensity ratio (FIR) offers significant advantages for rapid and non-contact temperature measurements. However, the application of optical temperature sensors is limited by the challenge of identifying advanced materials with high response sensitivity. In this study, phosphor and single-crystal states stoichiometric NaYb(MoO4)2 with Er3+ doping were prepared by solid-state reaction method and Czochralski method, respectively, for promising optical thermometry applications. The structure of the phosphor and single-crystal state samples were investigated. High-purity upconversion (UC) emissions were achieved from stoichiometric NaYb(MoO4)2:Er3+ samples with a maximum green-to-red ratio up to 70.3, which opens up numerous possibilities for their application as pure-green color converters. Besides, the UC emission spectra were monitored with respect to temperature, and the fluorescence intensity ratios (FIRs) of the 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions of Er3+ ions were investigated to evaluate the optical temperature sensing behaviors of NaYb(MoO4)2:Er3+. Importantly, the distinctions of optical temperature sensing behaviors between phosphor and single-crystal state samples were analyzed. The results suggest that stoichiometric NaYb(MoO4)2:Er3+, especially for single-crystal state NaYb(MoO4)2:Er3+, hold great promise as FIR-based optical temperature sensors. In addition, the results can also open up the research interests for employing stoichiometric materials and single crystal materials as optical thermometry applications.

Optical Thermometer Based on Efficient Near‐Infrared Dual‐Emission of Cr3+ and Ni2+ in Magnetoplumbite Structure

AbstractRecently, an optical thermometer based on the dual‐emitting fluorescent intensity ratio (FIR) in the visible light (VIS) region has achieved great development. However, there is very little progress in thermometers from NIR light. In this work, a novel optical thermometer based on highly efficient NIR dual‐emission of Cr3+ and Ni2+ in LaZnGa11O19 (LZG) with a magnetoplumbite structure is designed. Utilizing energy transfer from Cr3+ to Ni2+, the dual‐emission shows a wide coverage in the 650–1600 nm region, covering the NIR I and II windows, respectively. The as‐reported LZG:0.3Cr3+ and LZG:0.3Cr3+,0.01Ni2+ phosphors can reach internal/external quantum efficiency (IQE/EQE) of 94%/64% and 77%/53%, respectively. The electroluminescence property and potential applications in spectroscopic analysis, night‐vision, and bioimaging of fabricated NIR‐LED with LZG:0.3Cr3+,0.01Ni2+ have also been investigated. In addition, the designed ratiometric optical thermometer responds to wide temperature ranges (100‐175 K, 200–475 K) and shows a maximum relative sensitivity value (Sr) of 2.4% K−1 at 475 K. The optical performance of absorption in the red region and emission in the NIR region enables the LZG:0.3Cr3+,0.01Ni2+ to become a candidate for NIR optical thermometers in biotechnological applications.

Structural and luminescent performance and optical thermometry of Pr3+ doped SrWO4 down-conversion phosphors

A series of Pr3+ doped SrWO4 phosphors were synthesized using solid-state reaction routes. The phase composition, photoluminescence and temperature sensitivities of as-prepared materials were investigated. Rietveld refinement of measured XRD data was applied to analyze the lattice parameters. The optical transition was elaborated using UV–visible diffuse reflectance spectra and photoluminescence spectra. The photoluminescence measurements confirmed the strong visible light emission from the developed phosphors under both UV excitation at 250 nm and blue excitation at 450 nm. Notably, the maximum emission intensity was observed at a Pr3+ doping concentration of 2 mol%. Furthermore, the fluorescence intensity ratio (FIR) technique was employed, focusing on the emissions originating from the 3P0 and 1D2 state of Pr3+ within the temperature range of 298–598 K. Two FIR groups were adopted in this case, which can verify each other to achieve self-calibration. Typically, SrWO4:0.02Pr3+ exhibited remarkable performance as a temperature sensor, displaying an absolute sensitivity (Sa) of 3.11%K−1 and a relative sensitivity (Sr) of 0.81%K−1. As a result, the significant temperature-dependent PL and remarkable down-conversion luminescence make the SrWO4:Pr3+ material a promising candidate for optical thermometers and UV to visible converters of solar cell applications.

The Detection of Anthrax Biomarker DPA by Ratiometric Fluorescence Probe of Carbon Quantum Dots and Europium Hybrid Material Based on Poly(ionic)- Liquid.

Bacillus anthracis has gained international attention as a deadly bacterium and a potentially deadly biological warfare agent. Dipicolinic acid (DPA) is the main component of the protective layer of anthracis spores, and is also an anthrax biomarker. Therefore, it is of great significance to explore an efficient and sensitive DPA detection method. Herein, a novel ratio hybrid probe (CQDs-PIL-Eu3+) was prepared by a simple one-step hydrothermal method using carbon quantum dots (CQDs) as an internal reference fluorescence and a covalent bond between CQDs and Eu3+ by using a polyionic liquid (PIL) as a bridge molecule. The ratiometric fluorescence probe was found to have the characteristics of sensitive fluorescence visual sensing in detecting DPA. The structure and the sensing properties of CQDs-PIL-Eu3+ were investigated in detail. In particular, the fluorescence intensity ratio of Eu3+ to CQDs (I616/I440) was linear with the concentration of DPA in the range of 0-50 μM, so the detection limit of the probe was as low as 32 nm, which was far lower than the DPA dose released by the number of anthrax spores in human body (60 μM) and, thus, can achieve sensitive detection. Therefore, the ratiometric fluorescence probe in this work has the characteristics of strong anti-interference, visual sensing, and high sensitivity, which provides a very promising scheme for the realization of anthrax biomarker DPA detection.

N-UV triggered green emitting Er3+ doped Zirconia: A bifunctional material for solid-state lighting and optical thermometry

In the current piece of work, we have synthesized the Er3+-activated ZrO2 and illustrated the bifunctional utility of this material for solid-state lighting and non-contact optical thermometry. The synthesized samples were characterized by XRD, XPS, and PL techniques for their structural, surface, and luminescence studies. Under the excitation of 377 nm, characteristic green emission corresponding to intra 4f-4f transitions of Er3+ is obtained. The concentration quenching effect was observed beyond 1.2 mol % concentration of doping. Using Dexter's theory, it was revealed that dipole-quadrupole interactions are predominantly responsible for concentration quenching. The Photometric study was performed using the PL data. For the most intense phosphor, a highly pure green color (color purity ∼ 97.6%) and CCT ∼ 5375 K is observed. Furthermore, the temperature-sensing capability of the most intense sample has also been explored by triggering the synthesized phosphor by n-UV light. The temperature sensing performance is checked by measuring variations in the fluorescence intensity ratio (FIR) of the thermally coupled levels of Er3+ with temperature. The synthesized phosphor gives high relative sensitivity (1.19% K−1 at 303 K)) and absolute sensitivity (11.39 × 10−4 at 603 K)) values. These results suggest that n-UV-triggered Er3+ doped ZrO2 can be a promising bifunctional material for applications in solid-state lighting and non-contact optical thermometry.

A dual chemiluminescence and ratiometric fluorescence sensor based on WS2 QDs- Fe(II)- S2O82− system for bisphenol A detection

Bisphenol A (BPA) is an environmental containment with toxic and hazardous characteristics towards all organisms. So, introducing a simple and sensitive sensor for its determination in the field is of importance. We applied Fe(II) -S2O82− Fenton-like reaction to design chemiluminescence and fluorescence sensing methods for BPA detection. In the chemiluminescence method, tungsten disulfide quantum dots (WS2 QDs) were used as an enhancer to amplify (around 300-fold) the intensity of the ultra-weak Fe(II) -S2O82− CL reaction. The WS2 QD-enhanced CL system was applied to design a simple and sensitive sensor for monitoring BPA at the range of 1.0–50 μM. Additionally, a ratiometric fluorescence sensor was designed for BPA assay in which WS2 QDs and o-phenylenediamine (OPD) were applied as a reference and a fluorescence reporter, respectively. In the presence of BPA, the fluorescence intensity of ox-OPD, produced from the OPD-Fe(II) -S2O82− reaction, increased while that of WS2 QDs was almost constant. The ratio of reporter fluorescence intensity to that of the reference was linearly proportional to the BPA concentration in the range of 2.5–75 μM. The developed methods were successfully applied for the determination of BPA in water samples.

Validation of a multiplex microsphere immunoassay for detection of antibodies to Trypanosoma cruzi in dogs.

The vector-borne protozoan parasite Trypanosoma cruzi causes Chagas disease in humans, dogs, and many other mammalian hosts. Canine Chagas disease is increasingly diagnosed in dogs of the southern United States where triatomine insect vectors occur, and there are limited veterinary testing options; only the indirect fluorescent antibody (IFA) test is offered at a single accredited diagnostic laboratory. We evaluated a multiplex microsphere immunoassay (MIA) for the detection of antibodies against T. cruzi in dogs and compared it with existing serologic methods to establish cutoff values and relative sensitivity and specificity. We tested 135 canine sera that had been characterized using the IFA and off-label use of 2 commercial rapid assays with our multiplex MIA against 12 antigens: 9 T. cruzi antigens, a negative control recombinant protein (green fluorescent protein, GFP), a Leishmania antigen, and a canine parvovirus antigen (used as an antibody control given near-ubiquitous parvoviral vaccination). The median fluorescence intensity (MFI) ratio between each T. cruzi antigen and GFP was calculated for every sample. Samples with an antigen:GFP MFI ratio > 4 SDs above the mean of 25 known-negative sera were considered positive to that antigen. Samples testing positive to ≥ 2 antigens were considered positive for T. cruzi antibodies. Compared to the IFA, our multiplex MIA had a relative sensitivity of 100% and specificity of 97.0%. Given its precision, high-throughput format, potential for automation, and lack of subjective interpretation, our multiplex MIA should be considered a valid and improved assay for T. cruzi antibodies in dogs.

Achieving high-precision dual-mode temperature measurement in the photothermal conversion process of SrIn2O4: Er3+, Yb3+ phosphors

Accurate measurement of temperature during photothermal conversion is crucial for the application of up-conversion photothermal conversion fluorescent materials. In this paper, a kind of SrIn2O4: Yb3+, Er3+ up-conversion phosphor with strong photothermal conversion ability and high-precision dual-mode temperature measurement performance was synthesized by high-temperature solid-state method. Under 980 nm laser excitation, a high-precision temperature measurement with a maximum relative sensitivity of Sr = 1.2 %K−1 was achieved by using the fluorescence intensity ratio of the thermally coupled energy level pairs (2H11/2/4S3/2) of Er3+ ions. In addition, we found that the luminescent color of the synthesized phosphor can span a large color gamut interval with the rise of temperature, realizing the optical temperature measurement based on temperature-induced color coordinate shift. On this basis, we realized dual-mode temperature monitoring and temperature self-calibration during the photothermal conversion process of SrIn2O4: Yb3+, Er3+ phosphors. These results are of great practical value for the application of photothermal conversion fluorescent materials in micro-zone heating and temperature self-monitoring.

Optical behaviors of Mn4+-modified cubic type ZnTiO3:Eu3+ nanocrystals: Application in optical thermometers based on fluorescence intensity ratio and lifetime

Cubic type ZnTiO3 nanophosphors were fabricated by using hydrothermal method. The photoluminescence behaviors of Eu3+/Mn4+ co-doped ZnTiO3 crystals and Mn4+-modified ZnTiO3:Eu3+ crystals were investigated. The red and near-infrared emissions assigned to Eu3+ and Mn4+ were observed at the excitation wavelength of 465 nm for Eu3+/Mn4+ co-doped ZnTiO3 crystals and Mn4+ modified ZnTiO3:Eu3+ crystals. Eu3+/Mn4+ co-doped ZnTiO3 crystals revealed the most intense near-infrared emission assigned to Mn4+. For Mn4+-modified ZnTiO3:Eu3+ crystals, the red emissions assigned to Mn4+ revealed an obvious enhancement with the concentration of Mn4+ increasing from 0.01 mol% to 0.1 mol%, and then revealed a concentration quenching behavior at the Mn4+ concentration of 0.5 mol% and 1 mol%. Under 465 nm excitation wavelength, the emission assigned to 2Eg → 4A2g of Mn4+ in ZnTiO3 revealed stronger temperature dependence compared with that assigned to 5D0 → 7F2 transition of Eu3+. Based on the fluorescence intensity ratio between Eu3+ and Mn4+, the maximum relative sensitivity of 3.15 %/K at 305 K for the 0.05 mol% Mn4+ modified ZnTiO3:Eu3+ was achieved, which was higher than that of 2.9 %/K for Eu3+/Mn4+ co-doping ZnTiO3 nanocrystals. Based on the lifetime of the emission of Mn4+, the highest relative sensitivity of 1.4 %/K was obtained in the 0.05 mol% Mn4+ modified ZnTiO3:Eu3+, which was lower than that based on fluorescence intensity ratio. It indicated that the surface modification by transition metals should improve the temperatures sensing performance and had potential applications in optical thermometers.

Upconversion luminescence based temperature sensing properties and anti-counterfeiting applications of GdNbO4:Tm3+/Yb3+ phosphor

Pure monoclinic phase GdNbO4:Tm3+/Yb3+ phosphor was prepared using solid state reaction method for upconversion emission, optical thermometry, latent fingerprints visualization and anti-counterfeiting applications. The prepared phosphor exhibits colour tunability with temperature variation (from blue to almost white) and good suppression of thermal quenching. The temperature sensing characteristic from thermally and non-thermally coupled levels of Tm3+ ion were investigated using the fluorescence intensity ratio (FIR) approach. The result shows that the sensitivity for non-thermally coupled level is about ∼ 45 times higher than thermally coupled level. Latent fingerprint detection on various surfaces and anti-counterfeiting ink application were also shown upon 980 nm laser diode excitation. Above results indicate that the prepared GdNbO4:Tm3+/Yb3+ phosphor have applicability in the field of frequency upconversion, optical thermometry, color tunable devices, latent fingerprint visualization and anti-counterfeiting applications.

Fiber Optical Temperature Sensor Based on 980nm Excitation of CaWO4: Yb3+, Er3+ with Up-conversion Fluorescence Intensity Ratio

The Yb3+, Er3+ co-doped calcium tungstate materials were prepared. The temperature-sensitive fiber optic probes made from CaWO4:Yb3+, Er3+ were prepared by the high-temperature solid-phase sintering method. The XRD lattice structure of CaWO4: Yb3+, Er3+ was tested. The fluorescence spectra of the probe under 980nm excitation were tested, and the variable temperature profile of the probe was analyzed to derive its two-photon absorption process. The temperature characteristics of the up-conversion fluorescence intensity ratio (FIR) of the probe in the temperature range of 303-673K were investigated, and the results showed that this optical fiber probe can be used as a fiber optic temperature sensor with a linearity of 5.8% and a temperature measurement return difference of only 1.5%; it was found that the temperature characteristic curve of FIR of this fiber optic probe was reproducible. These properties show that CaWO4: Yb3+, Er3+ is feasible to be made into a fiber optic sensor.

Spectroscopic and temperature sensing properties of Sm3+ in self-activated CsLu(WO4)2 phosphors

In this research, a series of Sm3+ doped CsLu(WO4)2 phosphors was prepared via high temperature solid phase technique to design new red phosphors and optical thermometric materials. Their structures, morphology, band gap and luminescence properties were characterized by X-ray diffraction, scanning electron microscopy, diffuse reflection and luminescence spectra, respectively. Under UV excitation, CsLu(WO4)2 gives rise to a blue broad emission band between 350 and 700 nm, which stems from the 3T1u → 1A1g transition of WO66− groups. When Sm3+ is introduced into CsLu(WO4)2, energy transfer between WO66− groups and Sm3+ ions takes place in CsLu(WO4)2:Sm3+ phosphors, and color-tunable luminescence from blue to red is realized by controlling the Sm3+ doping concentration. The energy transfer efficiency between WO66− groups and Sm3+ ions was analyzed, and the energy transfer mechanism was determined to be dipole–dipole interactions. According to the temperature-dependent luminescence spectra, WO66− groups and Sm3+ ions exhibit large discrepancy in thermal quenching rates, and thus the temperature sensing properties of CsLu(WO4)2:Sm3+ in the temperature range of 283–403 K were analyzed. Based on the framework of fluorescence intensity ratio theory, the basic optical thermometry parameters including absolute and relative sensitivity of CsLu(WO4)2:Sm3+ were calculated and the results show that it has great potential for application in optical thermometry.

WO3 nanosheets with peroxidase-like activity and carbon dots based ratiometric fluorescent strategy for xanthine oxidase activity sensing and inhibitor screening

The abnormal level of xanthine oxidase (XOD) often causes pathological changes, which are related to a series of diseases. Herein, a novel and sensitive ratiometric fluorescent sensing platform based on WO3 nanosheets and carbon dots (CDs) was constructed to detect XOD activity for the first time. Under the catalytic oxidation of xanthine by XOD, hydrogen peroxide (H2O2) was generated. In the presence of H2O2, WO3 nanosheets were able to catalyze the oxidation of o-phenylenediamine to generate 2,3-diaminophenazine (DAP) with a yellow fluorescence signal at 570 nm due to its great peroxidase-like activity. The oxidation product DAP was capable of quenching the fluorescence of CDs at 430 nm through the inner filter effect. Therefore, the fluorescence intensity ratio F570/F430 can be used for quantitative analysis of XOD activity. This assay displayed good linear relationships in the range of 0.005–0.05 U/L and 0.5–40 U/L with a detection limit of 0.002 U/L. In addition, this ratiometric fluorescent sensing platform was successfully applied to the determination of XOD in human serum samples and XOD inhibitor screening, demonstrating significant potential in disease diagnosis and drug-screening applications.