Upconversion Fluorescence Emission Research Articles

Preparation and optical properties of rare earth fluoride and its related composite materials

Rare earth fluoride and its composite materials have shown broad application prospects in fields such as optoelectronics and photocatalysis. In this study, we prepared rare earth fluoride (β-NaYF4 nanocrystals) and its related composite materials (β-NaYF4/ZnO composite and GQDs@NaYF4 nanomaterials) using a solvothermal method and investigated their optical performance. The characterization and performance of the prepared materials were analyzed using a transmission electron microscope, X-ray diffraction, upconversion emission spectra, and fluorescence lifetime imaging microscopy. The results show that the crystal thickness of β-NaYF4 nanocrystals is approximately 45.0 nm when the F−: Ln3+ value is 6. Furthermore, X-ray diffraction analysis reveals that diffraction peak positions in β-NaYF4 nanocrystals correspond to the peak positions of standard card at different doping concentrations of Zn2+ Moreover, it was observed that the highest fluorescence lifetime of Tm3+ ion in 1G4 is 778 μs when the doping concentration of Zn2+ is 1 mol%. When the concentration of exonuclease III increases to 22.5U, the upconversion fluorescence emission intensity of GQDs@NaYF4 nanomaterial is about 34 ∗ 106 a.u. When the activation reaction time is 90 minutes, the upconversion emission intensity of GQDs@NaYF4 nanomaterial is about 37 ∗ 106 a.u. In conclusion, we successfully prepared rare earth fluoride and its composite materials with excellent optical properties through the solvothermal method.

Er3+/Yb3+/Ho3+ tri-doped no-core fiber temperature sensor based on fluorescence intensity ratio technology: towards high stability and accurate measurements.

In this paper, the green upconversion (UC) fluorescence emission from E r 3+/Y b 3+/H o 3+ tri-doped tellurite glass is investigated for temperature sensing. The doping of H o 3+ ions not only enhances the chance of energy level transition but also avoids the influence of the thermal effect caused by the proximity of 2 H 11/2 and 4 S 3/2 energy levels. The luminescence characteristics at different Y b 3+ and H o 3+ ion concentration doping molar ratios were investigated, and the strongest luminescence characteristics were exhibited when the Y b 3+ ion concentration was at 5mol% and H o 3+ at 0.2mol%. Based on this, a tri-doped T e O 2-Z n O-B i 2 O 3 (TZB) no-core fiber was fabricated and connected with multimode fibers (MMFs) to form a temperature sensor. The temperature sensing performance of the tri-doped TZB temperature sensor was evaluated in detail over the temperature range of 255-365K. The repeatability and stability of the temperature sensor was experimentally verified. The E r 3+/Y b 3+/H o 3+ tri-doped sensor can be used for noninvasive optical temperature sensing in the fields of environmental monitoring, biological sensing, and industrial process temperature control, etc.

Experimental optimization design synthesis for up-conversion luminescence performance in SrBi4Ti4O15: Er3+/Yb3+ red-green phosphors

Er3+/Yb3+ co-doped SrBi4Ti4O15 crystalline powders were synthesized using the high-temperature solid-phase method. The crystal structure of the obtained phosphors was analyzed through x-ray diffraction (XRD), confirming the purity of all products such as SrBi4Ti4O15. Employing experimental design optimization theory, regression equations were established to correlate the Er3+/Yb3+ doping concentrations with the luminescent intensities. The genetic algorithm was utilized to compute the optimal solutions of the equations, resulting in Er3+ and Yb3+ doping concentrations of 3 mol% (molar fraction) and 20 mol% under 980 nm laser excitation and 3 mol% and 29.79 mol% under 1550 nm laser excitation. The up-conversion fluorescence emission spectra of the samples were measured under 980 nm excitation, revealing intense green emissions at 525 nm, 550 nm, and 662 nm, corresponding to the 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 energy levels, respectively. Under 1550 nm excitation, peaks corresponding to the same energy levels were observed at 523 nm, 548 nm, and 661 nm. The relationship between the up-conversion fluorescence and the laser operating current for the optimal samples under 980 nm and 1550 nm excitations was explored, indicating two-photon and three-photon processes, respectively. Detailed analysis and discussion of the up-conversion fluorescence mechanisms were conducted. Additionally, the relationship between the up-conversion fluorescence and the temperature for the optimal samples was investigated, revealing excellent temperature sensing characteristics under 980 and 1550 nm laser excitations. The CIE coordinates for the optimal samples were calculated as (0.3111, 0.6747) and (0.5254, 0.4671) under 980 nm and 1550 nm excitations, respectively.

Transmissive fluorescent temperature sensor based on Er3+/Yb3+/Mo6+ tri-doped tellurite fiber for real-time thermal monitoring of motors using the FIR technique.

In this paper, we fabricate a transmissive fluorescent temperature sensor (TFTS) that based on Er3+/Yb3+/Mo6+ tri-doped tellurite fiber, which has the advantages of compactness and simplicity, corrosion resistance, high stability and anti-electromagnetic interference. The doping of Mo6+ ions will enhance the up-conversion (UC) fluorescence emission efficiency of Er3+ ions, thus improving the signal-to-noise ratio of TFTS. Using the fluorescence intensity ratio (FIR) technique, the real-time thermal monitoring performance of TFTS is evaluated experimentally. Apart from good stability, its maximum relative sensitivity is 0.01068 K-1 at 274 K in the measured temperature range. In addition, it is successfully used to monitor the temperature variation of the stator core and stator winding of the motor in actual operation. The results show that the maximum error between the FIR-demodulated temperature and the reference temperature is less than 1.2 K, which fully confirms the effectiveness of the TFTS for temperature monitoring. Finally, the FIR-based TFTS in this work is expected to provide a new solution for accurate and real-time thermal monitoring of motors and the like.

A ratiometric fluorescent fiber sensor based on integrated silica and tellurite glass for real-time human thermal monitoring

In this paper, we propose and demonstrate a portable fiber sensor with integrated tellurite and silica for dynamic human thermal monitoring, where Er3+/Yb3+ co-doped tellurite glass is employed to generate upconversion fluorescence emission related to thermally coupled energy levels via near-infrared excitation for ratiometric thermometry. The molten tellurite glass is extracted into a silica tube using the negative pressure approach, allowing for intimate adhesion between different glass materials with considerable softening temperature differences. With a fast instantaneous response of 0.4–0.6 s and an absolute error of −0.45–0.36 K, the sensor can accurately and timely capture small temperature fluctuations. The sensor is placed in the mouth or attached to the hand skin to measure the body temperature continually. It is also positioned in the mouth exhalation and nose breathing environments to monitor thermal activities in real-time, offering a new, highly reliable method for human health monitoring.

Luminescence enhanced temperature sensor based on the up-conversion emission in Er3+/Yb3+/Mo6+ tri-doped tellurite fiber

In this study, the green up-conversion (UC) fluorescence emission in Er3+/Yb3+/Mo6+ tri-doped tellurite glasses (TeO2–ZnO–Li2CO3–Bi2O3, TZLB) was explored for temperature sensing. The doping of Mo6+ ions allowed enhanced luminescence at moderate power pumping, avoiding the introduction of undesired laser-induced thermal effects while improving the spectral signal-to-noise ratio. The luminescence characteristics were investigated in detail at different doping molar ratio of Mo6+ ions, and the strongest was observed at 8 mol%. Drawing on tri-doped TZLB glass with the strongest UC emission intensity, a tri-doped TZLB fiber was fabricated and coupled with two multimode fibers (MMFs) via Ultraviolet (UV) adhesive, forming the temperature sensor. The sensor was further encapsulated by a silica tube sealed with Ultraviolet adhesive, overcoming the poor mechanical property of tellurite fiber. The temperature information could be demodulated based on the fluorescence intensity ratio technique. The temperature sensing performance of the tri-doped TZLB sensor was investigated as temperature varied from 258 to 420 K and its repeatability was experimentally verified. The Er3+/Yb3+/Mo6+ tri-doped TZLB has an application prospect in the field of lighting, and the so-based temperature sensor is expected to be applied to thermal detection in the fields of medical diagnostics, environmental monitoring, and optical thermometers, etc.

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.

Amplified UCNPs-Mitoxantrone dihydrochloride fluorescence PCR sensor based on inner filter for ultrasensitive and rapid determination of Salmonella typhimurium

A fluorescence sensor composed of alendronic acid (ADA) @upconversion nanoparticles (UCNPs) and mitoxantrone dihydrochloride (MTX) combined with polymer chain reaction (PCR) was developed for rapid, specific and ultrasensitive determination of Salmonella typhimurium. MTX, which has a wide absorption band at 500–700 nm, can completely overlap the upconversion fluorescence (UCF) emission spectrum, leading to the reduction of UCF intensity. By intercalating MTX into DNA structure, the absorption intensity of MTX is obviously weak. Thus, the concentration of target can be quantified by response change of UCF intensity based on inner filter (IFE) between UCNPs and MTX coupled with PCR. The sensitivity of sensor for detection of Salmonella typhimurium is improved due to IFE and PCR amplification process, with a detection limit of 11 CFU/mL. In addition, the UCNPs-MTX PCR fluorescence sensor has been applied to sensing Salmonella typhimurium in chicken samples with satisfied results. The research work revealed a rapid and sensitive analytical method for determination of Salmonella typhimurium and provided an insight for the construction of PCR fluorescence sensor.

Synthesis and luminescence investigation of SBA-15/NaYF4:Yb/Er composites

One of the main approaches toward obtaining efficient up converting materials with practical applications involves the development of composites with synergism between components. Herein, we reported an optical temperature sensing using up-conversion fluorescence emission at 530 and 550 nm in the Er3+/Yb3+-co-doped NaYF4 nanoparticles and SBA-15/NaYF4:Yb,Er composites excited at 976 nm. Nanoparticles and composites were prepared and investigated by X-ray diffractometry, N2 adsorption–desorption isotherms, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and up-conversion photoluminescence. Spherical like NaYF4:Yb,Er nanoparticles exhibited a mixture of hexagonal and cubic phases, while the rare earth ions incorporated inside of SBA-15 mesopores crystallized in a cubic phase. Optical thermometry property was investigated in the temperature range from 30 to 90 °C, and a maximum absolute sensitivity were 0.03/°C and 0.38/°C for nanoparticles and composites, respectively. The lower temperature range makes the composites with potential for application in biological systems.

Improving 2.0 μm fluorescence properties of Er3+/Ho3+ co-doped oxyfluoride silicate glass-ceramics containing YF3 nanocrystals by introducing Li+ ions for mid-infrared lasers

The enhancement of mid-infrared (MIR) fluorescence emission (1800–3000 nm) was achieved by adding Li+ ions into Er3+/Ho3+ co-doped oxyfluoride silicate glass-ceramics containing YF3 nanocrystals, which was prepared by conventional melt-quenching. The introduction of Li+ ion destroys the glass network [Si–O–Al] structure, and affects the crystallization ability of the substrate glass. In addition, the crystal field effect significantly enhances the up-conversion and MIR fluorescence emission of the prepared samples, with a decay time of 4.6 ms and the maximal absorption cross section (σabs) of 1.43 × 10−20 cm−2 at 1950 nm, as well as emission cross section (σem) of 1.73 × 10−20 cm−2 at 2021 nm. The results indicate that the prepared samples have excellent fluorescence properties and can be used for MIR lasers.

Thermal analysis and CW laser operation at 1.998 µm in end pumped Tm:YAP lasers

We report on thermal analysis and a continuous wave (CW) laser operation at (1.998µm) of end pumped Tm: YAP cylindrical laser rod. The Tm: YAP laser rod is pumped at a wavelength of 1.064 µm emitting from Nd: YAG laser source. A 3W incident pump power is used to generate a maximum laser output of 700 mW, representing 18% slope efficiency. The power of thermally induced lens in Tm:YAP laser rod is numerically analyzed and validated experimentally. The focal lengths of the thermally induced lens are directly measured using Shack-Hartmann wavefront sensor. We have detected blue up-conversion fluorescence emission before laser operation at 1.998 µm. The obtained experimental results were in good agreement with the numerical calculations. Full Text: PDF ReferencesI. F. Elder, J. Payne, "Diode-pumped, room-temperature Tm:YAP laser", Applied Optics 36 (33), 8606 (1997) CrossRef Y. Li, B. Yao, Y. Wang, Y. Ju, G. Zhao, Y. Zong, J. Xu, "High efficient diode-pumped Tm:YAP laser at room temperature", Chinese Opt. Lett. 5 (5), 286 (2007). DirectLink H. Ni, S. C. Rand, "Avalanche upconversion in Tm:YALO3", Opt. Lett. 16 (8), 1424 (1991). CrossRef Z. G. Wang, C. W. Song, Y. F. Li, Y. L. Ju, Y. Z. Wang, "CW and pulsed operation of a diode-end-pumped Tm:GdVO4 laser at room temperature", Laser Phys. Lett. 6 (2), 105 (2009). CrossRef Baoquan Yao, Yi Tian, Wei Wang, Gang Li, Yuezhu Wang, "Analysis and compensation of thermal lens effects in Tm:YAP lasers", Chinese Opt. Lett. 8 (10), 996 (2010). CrossRef F. Cornacchia, D. Parisi, C. Bernardini, M. Toncelli, "Efficient, diode-pumped Tm3+:BaY2F8 vibronic laser", Opt. Expr. 12 (9), 1982 (2004). CrossRef Xiaojin Cheng, Mi Fan, Jiandong Cao, Jianhua Shang, "Research on the thermal effect and laser resonator of diode-pumped thin-slab Tm:YAP lasers", Optik 176, 32 (2019). CrossRef W. Koechner, Solid-state Laser Engineering, Springer, (2013). DirectLink https://www.crytur.cz DirectLink http://www.laserlabcomponents.com/ DirectLink R. M. El-Agmy, N.AlHosiny, "2.31 [micro sign]m laser under up-conversion pumping at 1.064 [micro sign]m in Tm3+:ZBLAN fibre lasers", Elect. Lett. 46 (13), 936 (2010). CrossRef R. M. El-Agmy, N. M. Al-Hosiny, "870 mW blue laser emission at 480 nm in a large core thulium doped ZBLAN fiber laser", Laser Phys. 20 (4), 838 (2010). CrossRef R. M. El-Agmy, N. M. Al-Hosiny, "Power scaling of end-pumped Nd:YLF lasers, modeling and experiments", Optik 140, 584 (2017). CrossRef R. M. El-Agmy, N. Al-Hosiny, "Thermal analysis and experimental study of end-pumped Nd: YLF laser at 1053 nm", Photonic sensors 7 (4), 329 (2017). CrossRef S. C. Tidwell, J. F. Seamans, M. S. Bowers, A. K. Cousins, "Scaling CW diode-end-pumped Nd:YAG lasers to high average powers", IEEE J. Quantum Electron. 28, 997 (1992). CrossRef P. J. Hardman, W. A. Clarkson, G. J. Friel, M. Pollnau, D. C. Hanna, "Energy-transfer upconversion and thermal lensing in high-power end-pumped Nd:YLF laser crystals", IEEE Journal of Quantum Electronics 35, 647 (1999). CrossRef

Near-infrared photodetection based on erbium chloride borate nanobelts

Erbium compound materials have attracted enormous attentions due to their superior optical properties. Under near-infrared laser illumination at 1530 or 976 nm, these nanobelts exhibit efficient up-conversion fluorescence emission in visible region. A hybrid photodetector based on the synthesized erbium chloride borate nanobelts and a cadmium sulfide nanoribbon. The nice photoresponse of the photodetecor in the near-infrared region, especially in the communication band, is contributed by the effective radiative energy transfer from the erbium ions to the CdS semiconductor. This work provides a feasible basis for the application of rare earth compound nanostructure to high performance near-infrared photodetection devices.

Acute hepatotoxicity of multimodal targeted imaging contrast agent NaLuF4:Gd,Yb,Er-PEG/PEI-FA in mice.

In the past few decades, upconversion nanoparticles (abbreviated as UCNPs) have been more widely applied in the biomedical fields, such as in vitro and in vivo upconversion fluorescent bioimaging, photodynamic therapy, biological macromolecular detection, imaging mediated drug delivery and so on. But meanwhile, there is still not much research on the acute toxicity of upconversion nanoparticles in vivo, such as acute hepatotoxicity. In this work, we studied the in vivo biodistribution and acute hepatotoxicity of multimodal targeted contrast agent NaLuF4:Gd,Yb,Er-PEG/PEI-FA nanoprobe, which were synthesized by the solvothermal method and modified with Polyethylene glycol (PEG), Polyetherimide (PEI), folic acid (FA) on the surface. The acute hepatotoxicity in mice was systematically assessed after tail vein injection of different concentration of UCNPs. The results showed that NaLuF4:Gd,Yb,Er-PEG/PEI-FA nanoparticles with an average diameter of 44.5 ± 10.4 nm, and three typical upconversion fluorescence emission bands at 520 nm, 540 nm and 660 nm under the excitation of 980 nm laser. In vivo distribution experiments results demonstrated that approximately 87% of UCNPs injected through the tail vein accumulate in the liver. In the acute hepatotoxicity test, the intravenously injection dose of UCNPs was 10, 40, 70 and 100 mg/kg, respectively. The body weight, blood routine, serum biochemistry, histomorphology and liver oxidative stress were detected and observed no significant acute hepatotoxicity damage under the injection dose of 100 mg/kg. In conclusion, NaLuF4:Gd,Yb,Er-PEG/PEI-FA nanoprobes are safe and reliable, and have potential applications in the field of tumor targeted multimodal imaging.

Enhanced red upconversion fluorescence emission of Ho&lt;sup&gt;3+&lt;/sup&gt; ions in NaLuF&lt;sub&gt;4&lt;/sub&gt; nanocrystals through building core-shell structure

A series of the hexagonal-phase NaLuF&lt;sub&gt;4&lt;/sub&gt;:20.0%Yb&lt;sup&gt;3+&lt;/sup&gt;/2.0%Ho&lt;sup&gt;3+&lt;/sup&gt;/12.0% Ce&lt;sup&gt;3+&lt;/sup&gt;@NaLuF&lt;sub&gt;4&lt;/sub&gt;:&lt;i&gt;x&lt;/i&gt;%Yb&lt;sup&gt;3+&lt;/sup&gt; core-shell (CS) nanocrystals with codoping different Yb&lt;sup&gt;3+&lt;/sup&gt; ions in the shell is successfully built by a sequential growth process. The crystal structures and morphologies of samples are characterized by X-ray diffractometer and transmission electron microscope. With the Yb&lt;sup&gt;3+&lt;/sup&gt; ion concentration increasing from 0% to 15% in NaLuF&lt;sub&gt;4&lt;/sub&gt; shell, none of the crystal structures, sizes, and morphologies of the samples changes obviously because of the similarity in ionic radius between Yb&lt;sup&gt;3+&lt;/sup&gt; and the ions in shell and the low doping concentration. Under 980 nm near-infrared (NIR) excitation, the NaLuF&lt;sub&gt;4&lt;/sub&gt;:20.0%Yb&lt;sup&gt;3+&lt;/sup&gt;/2.0%Ho&lt;sup&gt;3+&lt;/sup&gt;/12.0%Ce&lt;sup&gt;3+&lt;/sup&gt; core nanocrystal produce green and red UC emission. And the red UC emission intensity is higher than green emission intensity. This is because two effective cross-relaxation processes happen between Ho&lt;sup&gt;3+&lt;/sup&gt; and Ce&lt;sup&gt;3+&lt;/sup&gt; ions, which results in the enhancement of the red emission. However, the overall emission intensity of NaLuF&lt;sub&gt;4&lt;/sub&gt;:20.0%Yb&lt;sup&gt;3+&lt;/sup&gt;/2.0%Ho&lt;sup&gt;3+&lt;/sup&gt;/12.0%Ce&lt;sup&gt;3+&lt;/sup&gt; nanocrystal decrease compared with that of the NaLuF&lt;sub&gt;4&lt;/sub&gt;:20.0%Yb&lt;sup&gt;3+&lt;/sup&gt;/2.0%Ho&lt;sup&gt;3+&lt;/sup&gt; nanocrystal. Thus, to further enhance the red UC emission intensity in NaLuF&lt;sub&gt;4&lt;/sub&gt;:20.0%Yb&lt;sup&gt;3+&lt;/sup&gt;/2.0%Ho&lt;sup&gt;3+&lt;/sup&gt;/12.0%Ce&lt;sup&gt;3+&lt;/sup&gt; nanocrystal, the NaLuF&lt;sub&gt;4&lt;/sub&gt;:20.0%Yb&lt;sup&gt;3+&lt;/sup&gt;/2.0% Ho&lt;sup&gt;3+&lt;/sup&gt;/12.0%Ce&lt;sup&gt;3+&lt;/sup&gt;@NaLuF&lt;sub&gt;4&lt;/sub&gt;:&lt;i&gt;x&lt;/i&gt;%Yb&lt;sup&gt;3+&lt;/sup&gt; CS nanocrystal are prepared for blocking the excitation and emission energy, transmitting surface quenching center and getting more excitation energy through doping Yb&lt;sup&gt;3+&lt;/sup&gt; ions in NaLuF&lt;sub&gt;4&lt;/sub&gt; shell. It can be clearly seen that the red UC emission intensity of CS nanocrystal first increases and then decreases with Yb&lt;sup&gt;3+&lt;/sup&gt; ion concentration increasing. Meanwhile, the corresponding red-to-green ratio increases from 4.9 to 5.6. The highest red UC emission intensity is observed in each of the NaLuF&lt;sub&gt;4&lt;/sub&gt;:20.0%Yb&lt;sup&gt;3+&lt;/sup&gt; /2.0%Ho&lt;sup&gt;3+&lt;/sup&gt;/12.0%Ce&lt;sup&gt;3+&lt;/sup&gt;@NaLuF&lt;sub&gt;4&lt;/sub&gt;:10%Yb&lt;sup&gt;3+&lt;/sup&gt; CS nanocrystal because the Ho&lt;sup&gt;3+&lt;/sup&gt; ions get more energy through the following three ways: 1) Yb&lt;sup&gt;3+&lt;/sup&gt; (core)-Ho&lt;sup&gt;3+&lt;/sup&gt; (core); 2) Yb&lt;sup&gt;3+&lt;/sup&gt; (shell)-Ho&lt;sup&gt;3+&lt;/sup&gt; (core); 3) Yb&lt;sup&gt;3+&lt;/sup&gt; (shell)-Yb&lt;sup&gt;3+&lt;/sup&gt; (core)-Ho&lt;sup&gt;3+&lt;/sup&gt; (core). Thus, building CS nanocrystals is one of the most effective approaches in order to improve the UC efficiency by suppressing the non-radiative decay of activators in the core and getting more excitation energy through different energy transfer ways. These NaLuF&lt;sub&gt;4&lt;/sub&gt;:20.0%Yb&lt;sup&gt;3+&lt;/sup&gt;/2.0%Ho&lt;sup&gt;3+&lt;/sup&gt;/12.0%Ce&lt;sup&gt;3+&lt;/sup&gt;@NaLuF&lt;sub&gt;4&lt;/sub&gt;:Yb&lt;sup&gt;3+&lt;/sup&gt; CS nanocrystals with red UC emission have great potential applications in biological field and multi-primary color.

Preparation of core-shell magnetic nano-upconversion materials and its targeting effect

In this paper, magnetic upconversion Fe3O4@SiO2@NaGdF4:Yb,Er (UCP) composite particles were prepared by Fe3O4@SiO2-NH2 nanoparticles reacting with NaGdF4:Yb,Er modified by α-bromoisobutyric acid for the first time. The products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), EDS and fluorescence spectrum. The results show that UCP composite nanoparticles have upconversion fluorescence emission peaks as NaGdF4:Yb,Er but weaker emission intensity. In contrast to NaGdF4:Yb,Er@Fe3O4 particles, UCP composite nanoparticles have better fluorescence luminescence properties, but poor magnetic properties. Biological distribution and magnetic nano-uptake of radioactive in mouse show nanomagnetic UCP particles loaded with drugs can be accumulated in the tumor site of spleen and pancreas by magnetic controlled targeting, in order to achieve drug magnetic targeted therapy.

Core-Shell-Shell Multifunctional Nanoplatform for Intracellular Tumor-Related mRNAs Imaging and Near-Infrared Light Triggered Photodynamic-Photothermal Synergistic Therapy.

A multifunctional nanoplatform, which generally integrates biosensing, imaging diagnosis, and therapeutic functions into a single nanoconstruct, has great important significance for biomedicine and nanoscience. Here, we developed a core-shell-shell multifunctional polydopamine (PDA) modified upconversion nanoplatform for intracellular tumor-related mRNAs detection and near-infrared (NIR) light triggered photodynamic and photothermal synergistic therapy (PDT-PTT). The nanoplatform was constructed by loading a silica shell on the hydrophobic upconversion nanoparticles (UCNPs) with hydrophilic photosensitizer methylene blue (MB) entrapped in it, and then modifying PDA shells through an in situ self-polymerization process, thus yielding a core-shell-shell nanoconstruct UCNP@SiO2-MB@PDA. By taking advantages of preferential binding properties of PDA for single-stranded DNA over double-stranded DNA and the excellent quenching property of PDA, a UCNP@SiO2-MB@PDA-hairpin DNA (hpDNA) nanoprobe was developed through adsorption of fluorescently labeled hpDNA on PDA shells for sensing intracellular tumor-related mRNAs and discriminating cancer cells from normal cells. In addition, the fluorescence resonance energy transfer from the upconversion fluorescence (UCF) emission at 655 nm of the UCNPs to the photosensitizer MB molecules could be employed for PDT. Moreover, due to the strong NIR absorption and high photothermal conversion efficiency of PDA, the UCF emission at 800 nm of the UCNPs could be used for PTT. We demonstrated that the UCNP@SiO2-MB@PDA irradiated with NIR light had considerable PDT-PTT effect. These results revealed that the developed multifunctional nanoplatform provided promising applications in future oncotherapy by integrating cancer diagnosis and synergistic therapy.

Enhancing Upconversion Luminescence of LiYF4:Yb,Er Nanocrystals by Cd2+ Doping and Core–Shell Structure

In this work, we report a phenomenon that upconversion emission intensity of Er3+ was enhanced by cadmium. Cd2+ was taken with 0, 3, 10, 20, 30, and 40 mol % as a new dopant to codope LiY0.78Yb0.20Er0.02F4, meanwhile the doping effects on the crystal structure, morphology, and upconversion fluorescence emission are investigated by XRD, Rietveld refinement, TEM, and upconversion spectroscopy analysis methods in detail. The green upconversion emission intensity was enhanced, and the maximum emission intensities were enhanced to twice when 10 mol % Cd2+ was codoped into tetragonal LiYF4, while its decay lifetime was reduced. Additionally, we further designed the synthesis of the homogeneous LiYF4:20%Yb,2%Er,10%Cd@LiYF4 of which the emission intensity is 11 times higher than that of the Cd2+-free nanocrystals, meanwhile an intriguing morphology of core–shell nanocrystals was obtained. This investigation may be useful for the design and improvement of upconversion materials for fulfilling the prerequisite of t...

Tuning upconversion fluorescence emission of -NaLuF4:Yb3+/Ho3+ nanocrystals through codoping Ce3+ ions

Rare-earth-doped up-conversion (UC) fluoride materials have been widely used in phosphors, color displays, optical storages, solid-state lasers, solar cells and biomedical imaging, due to the fact that their low phonon energy can effectively suppress the nonradiative multiphonon relaxation process. In this work, the NaLuF4:Yb3+/Ho3+ nanocrystals are successfully synthesized by a facile solvothermal method. The crystal structure and morphology of the NaLuF4 nanocrystals are characterized by the X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) respectively. The diffraction peaks are well consistent with those of high-purity hexagonal NaLuF4 (JCPDS No. 77-2042, P63/m space group). The TEM image reveals that the product is composed of monodisperse hexagonal rods with an average length of about 170 nm and an average diameter of 30 nm. The crystal structure and morphology do not present obvious change with the increasing Ce3+ ion concentration, which is due to the similarity in ion radius between Ce3+ and Lu3+. Under 980 nm excitation, the UC emissions of -NaLuF4:Yb3+/Ho3+ nanocrystals with different Ce3+ codoping concentrations are carefully studied. The strong green and red UC emissions of Ho3+ ions are observed in -NaLuF4 nanocrystals. It can be found that the UC emission of Ho3+ ions is tuned from green to red in -NaLuF4 nanocrystals through increasing Ce3+ ion concentrations from 0 to 12%, and the red-to-green (R/G) ratio is enhanced from 0.34 to 8.44. According to the level structure of Ho3+ ions, the red UC emission originates from the excited state 5F5. However, the population of the 5F5 excited state mainly depends on the two nonradiative relaxation processes of 5S2/5F45F5 and 5I65I7 transitions. In fact, the two nonradiative relaxation processes are very difficult to occur according to multiphonon nonradiative relaxation rate. When Ce3+ ion is introduced into the system, the red UC emission intensity and R/G ratio of Ho3+ are increased, because the energy gap from the excited state 5F7/2 to the ground state 2F5/2 is about 3000 cm-1 for Ce3+ ions, which is similar to the gaps of 5S2/5F45F5 and 5I65I7 transitions of Ho3+ ions. According to the energy conservation law, the two inefficient nonradiative processes from the 5S2/5F4 and 5I6 states of Ho3+ ions are substituted in order by resonant cross relaxation (CR) processes 5S2 (5F4) (Ho3+) + 2F5/2 (Ce3+5F5 (Ho3+) + 2F7/2 (Ce3+) and 5I6 (Ho3+) + 2F5/2 (Ce3+)5I7 (Ho3+) +2F7/2 (Ce3+) between Ho3+ and Ce3+ ions. These two resonant CR processes can transfer populations from the 5S2/5F4 state and 5I6 state to the 5F5 state and its intermediate 5I7 state, respectively. The resonant modality and the strong interaction between Ho3+ and Ce3+ ions are employed to enhance the red emission and suppress the green emission. The occurrence of CR process between Ho3+ and Ce3+ ions is further proved by the down-conversion emission spectra of Ho3+ ions under 532 and 980 nm laser excitation, respectively. We demonstrate that the highly efficient red UC emission of -NaLuF4:Yb3+/Ho3+/Ce3+ nanocrystals offers opportunities as desired optical materials for color displays, anticounterfeiting techniques and multiplexed labeling applications.

Dual-Mode Luminescent Nanopaper Based on Ultrathin g-C3N4 Nanosheets Grafted with Rare-Earth Upconversion Nanoparticles.

Ultrathin graphite-like carbon nitride (g-C3N4) nanosheets have attracted considerable attention due to the enhanced intrinsic photoabsorption and photoresponse with respect to bulk g-C3N4. For the first time, a dual-mode of down- and upconversion luminescent g-C3N4 nanopaper with high optical transparency and mechanical robustness was successfully fabricated through a simple thermal evaporation process using chitosan as a green cross-linking agent. The dual-mode of down- and upconversion fluorescence emission originated from the amino terminated ultrathin g-C3N4 nanosheets functionalized with carboxylic acid modified multicolored rare-earth upconversion nanoparticles (cit-UCNPs) via EDC/NHS coupling chemistry. The homogeneously distributed cit-UCNPs@g-C3N4 nanoconjugates with excellent hydrophilicity displayed good film-forming ability and structural integrity; thus, the photoluminescence of each ingredient was substantially maintained. Results indicated that the freestanding chitosan cross-linked cit-UCNPs@g-C3N4 luminescent nanopaper possessed high transmittance, excellent mechanical properties, and remarkable dual-mode emission. The smart design of high performance luminescent nanopaper based on ultrathin g-C3N4 nanosheets grafted with multicolored UCNPs offers a potential strategy to immobilize other multifunctional luminescent materials for easily recognizable and hardly replicable anticounterfeiting fields.

Dissolution Mechanism of Upconverting AYF4:Yb,Tm (A = Na or K) Nanoparticles in Aqueous Media.

The dissolution of upconverting AYF4:Yb,Tm (A = Na or K) nanoparticles (UCNPs) in aqueous media was systematically studied. UCNPs with a cubic structure and sizes of between 10 and 33 nm were synthesized solvothermally in ethylene glycol at 200 °C. The UCNPs of both compositions showed an upconversion fluorescence emission characteristic of Tm(3+). The effects of the A cation, the particle size, the temperature, the pH, and the composition of the aqueous medium on the dissolution of the UCNPs were evaluated. The degree of dissolution was determined from the fraction of dissolved fluoride (F(-)) using potentiometry. Unexpectedly, the composition of aqueous media had the most significant effect on the dissolution of the UCNPs. The highest degree of dissolution and rate were measured for the phosphate-buffered saline (PBS), which can be explained by the formation of stable lanthanide compounds with phosphates. The degree of dissolution was much lower in water and in the phthalate buffer, which was attributed to the release of F(-) as a result of the hydrolysis of the UCNPs' surfaces.