980-nm Laser Excitation Research Articles

Design and electrospinning synthesis of SrF2:Er3+/Yb3+ unidimensional nanostructural materials with tunable upconverting fluorescence

In order to develop new morphology and properties of up-converting fluorescent materials, SrF2:Er3+/Yb3+ up-converting fluorescent unidimensional nanostructural materials including nanofibres, nanostrips and hollow nanofibres have been designed and successfully constructed via a uniaxial electrospinning associated with a bi-crucible fluorination technology. Controllable fabrication of unidimensional nanostructural materials is successfully realized via controlling the ingredients and proportions of the spinning solutions and spinning parameters. The influences of roasting temperature, molar proportion of Yb3+ to Er3+ and morphology on the up-converting fluorescence of the samples are studied in detail, and further tunable fluorescence is achieved. Upon the excitation of 980-nm laser, the unidimensional nanostructural materials display excellent up-converting fluorescence. The bright green emissions at 526 and 548 nm are assigned to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 energy levels transition of the Er3+ ions, respectively, and the weaker red characteristic emission peak at 652 nm is attributed to the 4F9/2 → 4I15/2 energy level transition of Er3+. Further, the detailed fluorescent mechanism and the formative mechanism of the unidimensional nanostructural materials are expounded in-depth, and the fabrication techniques are built. Much more importantly, the designing philosophy and fabricating technology can be popularized to manufacture other metal fluoride unidimensional nanostructural materials. The as-synthesized SrF2:Er3+/Yb3+ unidimensional nanostructural materials may find tremendous potential applications in the areas of emitting diodes, displaying devices, optical probes, bioimaging, sensing, drug delivery and lithium-sulfur batteries.

Simultaneous fluorometric and chirality based aptasensing of sulfamethazine by using upconversion nanoparticles and Au@Ag@Au core-shell nanoparticles.

A dual-mode aptasensor was employed for ultrasensitive determination of sulfamethazine (SMZ). The assay is based on simultaneous quantification by using fluorometry and chirality. The aptamer against SMZ was immobilized on upconversion nanoparticles (UCNPs) while the complementary DNA of SMZ aptamer was immobilized on Au@Ag@Au core-shell nanoparticles (Au@Ag@AuNPs). Based on complementary base-pairing reactions, the aptamer of SMZ and its complementary DNA sequence (cDNA) were hybridized to form duplex structure. Thus, Au@Ag@AuNPs and UCNPs were in close proximity. Efficient inner filter effect (IFE) from UCNPs (energy donor) to Au@Ag@AuNPs (energy acceptor) occurred under the excitation of 980nm laser. In the presence of targets (SMZ), as the aptamer of SMZ coupled with SMZ to form stable complex structure. As a result, the hybridization of aptamer and its cDNA deceased and the fluorescence signal recovered. Furthermore, as the degree of the assembly decreased, the circular dichroism (CD) signal also decreased. Fluorescence was measured at excitation/emission wavelengths of 980/655nm. The linear ranges for detection of SMZ are between 0.10-100ng·mL-1 and 1.00-100ng·mL-1 for the fluorescence and circular dichroism modes, respectively. The method was applied to the determination of SMZ in spiked milkwith high recoveries. Conceivably, it can be extended to the analysis of numerous other targets for which adequate antibodies or aptamers are available. Graphical abstract Schematic representation of a chirality assay and a fluorometric assay based on inner filter effect (IFE) between upconversion nanoparticles (UCNPs) and Au@Ag@Au core-shell nanoparticles (Au@Ag@AuNPs) for the determination of sulfamethazine (SMZ).

Upconversion luminescence of ytterbium and erbium co-doped gadolinium oxysulfate hollow nanoparticles

Here we report the successful preparation of upconversion (UC) gadolinium oxysulfate (Gd2O2SO4) hollow nanoparticles with sensitizer Yb3+ and activator Er3+ co-doped through a biomolecule-assisted hydrothermal route and followed by calcination. By changing the experimnetal parameters, including the reaction temperature and surfactant type and concentration, the particle size and morphology can be regulated. Under the excitation of 980nm laser, the red-to-green (R:G) emission intensity ratio is about 21:1, indicating the red emission color of 90%Gd2O2SO4:9%Yb3+,1%Er3+ hollow nanoparticles. The influence of the low temperature on luminescence is interpretated with enegy transfer mechanism. The red emission color and long lifetime at red emission regions enable their promising advanced luminescence microscopy applications.

Enhanced Up-Conversion Emission in Al3+ Co-Doped ZnGa2O4:Yb3+,Tm3+ Powder Phosphors.

Yb3+-Tm3+ co-doped up-conversion powder phosphors using Zn(AlxGa1-x)2O4 (ZAGO) as the host materials were synthesized via solid-state reaction successfully. In addition, the morphology, structural characterization and up-conversion luminescent properties were all investigated by scanning electron microscope (SEM), x-ray diffraction (XRD) and fluorescence spectrophotometer (F-7000), respectively. Under the excitation of a 980nm laser, all as-prepared powders can carry out blue emission at about 477nm (corresponding to 1G4→3H6 transition of Tm3+ ions), and red emission at about 691nm (attributed to 3F3→3H6 transition of Tm3+ ions). Also, the influence of doping Al3+ ions were investigated. In brief, the doping of Al3+ ions has no effect on the position of emission peak. Howbeit the up-conversion efficiency and intensity of ZAGO:Yb,Tm phosphors are stronger than ZGO:Yb,Tm and ZAO:Yb,Tm phosphors, while the crystallinity is the opposite. More particularly, all as-prepared powder phosphors emit strong luminescence, which is observable by the naked eye, demonstrating the potential applications in luminous paint, luminescent dye, etc.

Mechanism of ultraviolet upconversion luminescence of Gd3+ ions sensitized by Yb3+-clusters in CaF2:Yb3+, Gd3+

Ultraviolet (UV) luminescence under the near infrared (NIR) excitation is very important for the photodynamic therapy and NIR photocatalysis. In this paper, UV emission of Gd3+ ions in CaF2:Yb3+, Gd3+ excited by 980nm laser is studied theoretically on the basis of the cooperative energy transfer from excited lanthanide tetramers. The main mechanism for the cooperative energy transfer from an excited Yb3+-tetramer to a Gd3+ ion is dq-dq-qq (d means an electric dipole and q means an electric quadrupole) and the energy transfer rate is calculated to be 1.7 × 10−6s−1, which is well comparable with the previous calculated cooperative luminescence rate of 1.8 × 10−6s−1 from an Yb3+-trimer. This is reasonably agreed with our previous experimental result that showed UV luminescence of Gd3+ ions and Yb3+-trimers within the same order of magnitude in CaF2:Yb3+, Gd3+ under the excitation of 980nm laser. The present paper suggests that CaF2:Yb3+, Gd3+ is a potential up-conversion luminescent material for UV, and stimulates the design and development of new UV luminescent phosphors sensitized by lanthanide ion clusters.

Realizing nearly pure green and red emissions of Ho3+/Yb3+ co-doped Gd2(MoO4)3 through tri-doping Eu3+ and Ce3+

The nearly pure green and red emissions of Ho3+/Yb3+ co-doped Gd2(MoO4)3 were realized by tri-doping Eu3+ and Ce3+, respectively. The Ho3+/Yb3+ co-doped Gd2(MoO4)3 powder, radiating intense green and red emissions, was prepared by a typical sol-gel method. Under the excitation of 980nm laser, the red-to-green ratio was tuned from 0.2 to 4 as the concentration of Eu3+ changed from 6 to 0mol%, attributed to the energy transfer processes between Ho3+ and Eu3+. Meanwhile, the red-to-green ratio altered from 4 to 20 as the concentration of Ce3+ changed from 0 to 20mol% via the cross relaxing processes between Ho3+ and Ce3+. The prepared phosphors, possessing large tuning range of red-to-green ratio and resisting high temperature, can be potentially applied to colorful display and solid-state lighting.

Spectroscopic and pump power dependent color-tunable upconversion studies of Yb3+/Er3+-doped Sr2ScF7

Er3+ and/or Yb3+ doped Sr2ScF7 up-conversion (UC) phosphors were synthesized, and the optimum doping concentrations of Yb3+ and Er3+ in the Sr2ScF7 host were found to be 20% mol and 7% mol, respectively. Under excitation of 980nm laser, the UC spectra of the samples is composed of three green emission bands from 510 to 570nm centered at 525, 543 and 551nm and two red emission band from 640 to 690nm with two peaks at 657 and 671nm, which is attributed to the 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+, respectively. The UC emission color of Er3+ can be tuned by adjusting the intensity ratio of red to green emission through manipulating the population of red and green emitting states.

Pure red upconversion emission from CaF2:Yb3+/Eu3+

Single phase cubic CaF2 microcrystals co-doped with Eu3+ and Yb3+ ions were synthesized through a coprecipitation process followed by annealing at 1200°C. Under the excitation of 980nm laser, the intensive emission at ~614nm (5D0 → 7F2) in the red region was observed at room temperature. The color coordinate of CaF2:0.1%Yb3+/0.1%Eu3+ was calculated with the Commission Internationale de I’Eclairage (CIE) chromaticity coordinate of (x=0.572, y=0.265). The excitation of Eu3+ ions came from the energy transfer of Yb3+-dimers through a cooperation sensitization process. Furthermore, not only the emissions from the 5Di (i=0, 1, 2, 3)→7Fj (j=0, 1, 2, 3) transitions but also the rarely reported emission (~398nm) from the 5L6 →7F0 transition was recorded. The cooperation sensitization process was so effective in the Yb3+/Eu3+ co-doped system that all the cooperative luminescence (CL) from Yb3+-clusters were quenched and only the red upconversion luminescence of Eu3+ ions could be seen.

Optical temperature sensing properties of Er3+, Yb3+ co-doped NaGd(MoO4)2 phosphor

Er3+, Yb3+ co-doped NaGd(MoO4)2 phosphors by using sodium citrate as chelating agent were synthesized by hydrothermal method. The structure and morphology were characterized by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The temperature-dependent up-conversion spectra of Er3+, Yb3+ co-doped NaGd(MoO4)2 phosphor under the excitation of 980nm laser with different ratios of Cit3−/Re3+ has been measured. It was found that the Cit3−/Re3+ ratio considerably influenced the sample's morphology. The temperature sensing performance for the samples with various morphologies was studied based on the change of emission intensities from two thermally coupled 2H11/2 and 4S3/2 levels of Er3+. It was found that the temperature sensitivity can up to a relative high value of 0.0161K−1, which was obtained for the sample with the ratio of Cit3−/Re3+ was 0.5. Finally, physical mechanism of morphology-dependent temperature sensing sensitivity was explained and predicted.

Synthesis and Up-Conversion Luminescent Properties of Na(Y<sub>1.5</sub>Na<sub>0.5</sub>)F<sub>6</sub> Hexagonal Prism

Na (Y1.5Na0.5)F6 microparticks were prepared by hydrothermal method. EDTA as the chelating agent. The samples were characterized by X-ray diffraction, scanning electron microscopy and fluorescence spectrometer. The X-ray diffraction indicates that the crystal shows a hexagon phase structure. Under the excitation of 980nm laser, the Na (Y1.5Na0.5)F6 exhibited strong up-conversion light: 4F9/2→4I15/2(red), 4H11/2/4S3/2→4I15/2(green) and 4G11/2→2H9/2 (near-ultraviolet).

Localization induced intense red upconversion luminescence in monodispersed K3ZrF7:Yb3+/Er3+ nanocrystals

There are increasing demands for upconversion (UC) nanocrystals since they are found to have important applications in the field of bio-imaging. Herein, novel monodispersed Yb3+/Er3+ co-doped K3ZrF7 nanocrystals with tunable sizes of 6–30nm were prepared by high temperature co-precipitation method. Intense UC emission of Er3+ with large red to green ratio was obtained under the excitation of 980nm-laser due to the cation localization effects. The UC luminescent lifetimes of 4S3/2 and 4F9/2 were determined to be 0.137 and 0.217ms, respectively. At last, the possible upconversion mechanism was proposed basing on the pump power dependent UC luminescence experiments.

Er3+/Yb3+ co-doped bioactive glasses with up-conversion luminescence prepared by containerless processing

Er3+/Yb3+ co-doped bioactive glasses were prepared via containerless processing in an aerodynamic levitation furnace. The as-prepared glasses were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) equipped with energy dispersive X-Ray spectroscopy (EDX). The up-conversion luminescence of as-prepared glasses was measured using an Omni- 3007 spectrometer. Furthermore, the in vitro bioactivity was evaluated by soaking the materials in simulated body fluid, and the biocompatibility was evaluated in MC3T3-E1 cell culture.The results show that containerless processing is a unique method to prepare homogeneous rare earth doped bioactive glasses. The obtained Er3+/Yb3+ co-doped glasses show green and red up-conversion luminescence at the excitation of 980nm laser. The XRD analysis confirmed that calcium silicate powders, as starting materials, were completely transformed from the original multi-crystalline phase (CS-P) into the amorphous-glassy phase (CS-G, EYS, LCS) via containerless processing. The SEM observation combined with EDX and FTIR analyses showed that the as-prepared glasses were bioactive. The cell proliferation assay also revealed that the as-prepared glasses were biocompatible and nontoxic to MC3T3-E1 cells. This study suggests that the luminescent bioactive glasses prepared by containerless processing could be used for studying biodegradation of bone implantation materials.

Temperature and concentration effects on upconversion photoluminescence properties of Ho3+ and Yb3+ codoped 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 multifunctional ceramics

Ho3+ and Yb3+ codoped lead magnesium niobate–lead titanate (PMN–PT) ceramics with various doping concentration have been fabricated by conventional solid reaction method. Under the excitation of 980nm laser, as-synthesized samples exhibit bright yellow-green upconversion (UC) luminescence. Their UC photoluminescence properties were investigated by the emission spectra with respect to various concentration of Ho3+ and Yb3+. Results show that optimal luminescent concentration was obtained in 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 ceramics codoped with 0.5mol% Ho3+ and 2mol% Yb3+ (abbreviated as 67PMN–33PT:2Yb,0.5Ho). The possible mechanism of UC emission was discussed by energy level diagrams of Ho3+ and Yb3+ ions according to the dependence of integrated intensity of UC emission bands on pumping power. Furthermore, the temperature dependence of UC emission intensity of 67PMN–33PT:2Yb,0.5Ho sample was investigated in detail in the range of 25–180°C under excitation by a 980 diode laser. According to Arrhenius formula, the fitting result of the effect of temperature on integrated intensity of emission band was coinciding well with the experiment results. It is shown that the emission intensity depends strongly on temperature, which has excellent relative sensitivity with its maximum value of 0.77%K−1 at 93°C. These indicate that the 67PMN-33PT:2Yb,0.5Ho ceramic may be useful for temperature sensing and optical-electrical devices as a multifunctional material.

Preparation and near-infrared luminescence properties of Y2O3:Er3+, Yb3+ nanopowders

Y2O3:Er3+, Yb3+ nanopowders were prepared by co-precipitation method. The properties of the samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy and spectrophotometer. No impurity was found in the synthesized materials. The grain size of the powders increased greatly with the increase of temperature. The samples showed obvious near infrared emission peaking at 1535nm under the excitation of 980nm laser, which was assigned to the 4I13/2→4I15/2 energy level transition of Er3+. The superabundant doping content of Er3+ decreased the luminescence intensity obviously because of the concentration quenching of Er3+. With a low doping content of Yb3+, the reinforced green, near infrared and the weakened red luminescence were observed. However, the condition was reversed when the Yb3+ increased to a certain higher concentration.

Facile Template Free Synthesis and Tunable RGB Luminescent Properties of Ln3+-Doped Yttrium Oxide Nanospheres

Well-dispersed and uniform Y2O3:Ln3+ (Ln3+ = Eu3+/Tb3+/Yb3+/Er3+/Tm3+) nanospheres have been successfully prepared at 180°C via a facile hydrothermal route without any template, followed by a subsequent calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and cathodoluminescence (CL) spectra as well as kinetic decay were employed to characterize the samples. It was found that the hydrothermal precursor could act as a template to obtain the corresponding oxide Y2O3 which inherited the original morphology of the hydrothermal precursor. The TEM and SEM images indicate that the samples consist of separated spheres with a mean diameter of about 260 nm. Under the excitation of ultraviolet (UV) light, 980-nm laser, and low-voltage electron beams, the Y2O3:Ln3+ phosphors all exhibited bright red, green and blue emissions, respectively, which were easily observed by naked eyes. The corresponding luminescent mechanism had been discussed. Due to the excellent PL (including up-conversion and down-conversion) and CL properties, multicolor tunable luminescence, ideal spherical shape, and cheap Y2O3 host, the as-prepared phosphors can potentially be used as fluorescent lamps, up-conversion fluorescent labels, and field emission display devices.

Hydrothermal Synthesis and Green Luminescent Properties of Lu<SUB>2</SUB>O<SUB>3</SUB>:Yb<SUP>3+</SUP>/Ho<SUP>3+</SUP> Nanocubes

Uniform and dispersive Lu2O3:Yb3+/Ho3+ nanocubes have been successfully synthesized by the hydrothermal process followed by a subsequent calcination at 800 degrees C. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), cathodoluminescence (CL) spectra, as well as lifetimes measurements were utilized to characterize the synthesized phosphors. The as-formed RE(3+)-doped lutetium oxide precursor via the hydrothermal process as a template could transform to RE(3+)-doped Lu2O3 with their original cubic morphology and slight shrinkage in the size after the post-annealing process. The formation mechanism for the lutetium oxide precursor cubes has been proposed. Under the excitation of UV light, 980-nm laser and low-voltage electron-beams, Lu2O3:Yb3+/Ho3+ phosphors all show the characteristic emission of the Ho3+ ion (5F4, 5S2 --> 18 transition) withgreen color, which is easily observed by naked eyes. The corresponding luminescent mechanisms have been discussed. Due to the excellent PL (including up-conversion and down-conversion) properties and CL properties of the Lu2O3:Yb3+/Ho3+ phosphors, they are potentially applicable in fluorescent lamps, up-conversion fluorescent labels and FED devices as an efficient green phosphor.

Tunable upconversion emission in Ba2YF7:Yb3+/Er3+ nanocrystals with different Yb3+ concentration

Ba2YF7:xYb3+,0.02Er3+ nanocrystals with different Yb3+ concentration (x=0.2, 0.4, 0.6, 0.8, 0.98) were synthesized via a solvothermal method. Their X-ray diffraction patterns reveal that all the samples are cubic phase without phase change at arbitrary Yb3+ concentration. Upon excitation of 980nm laser, these nanocrystals display upconversion emission in the green and red spectral regions. The relative emission intensity at these two regions can be tuned by Yb3+ concentration. To investigate the effect of Yb3+ ion, the decay times of 650nm emission were measured and analyzed. Ba2YF7:0.6Yb3+,0.02Er3+ nanocrystals have the longest lifetime and highest emission intensity among all the samples. We concluded the lifetime of 4F9/2 level has an effect on its own population and intensity ratio of red and green emission. Our results show Yb3+ ion can tune the upconversion emission and improve upconverison emission intensity.

Controllable synthesis, upconversion luminescence, and paramagnetic properties of NaGdF4:Yb3+,Er3+ microrods

Hexagonal phase NaGdF4 microrods have been successfully synthesized via a facile hydrothermal method with ethylene diamine tetraacetic acid (EDTA) as the structure-directing agent. The additive amounts of NaF and NaNO3 as well as the reaction time have great effect on the morphology evolution of the products. A possible growth mechanism was proposed for the formation of β-NaGdF4 microrods. Under the excitation of 980nm near-infrared laser, bright green upconversion (UC) emissions can be readily achieved from NaGdF4:10%Yb3+,1%Er3+ microrods. In addition, the NaGdF4 microrods exhibit excellent paramagnetic features with the magnetization value of 5.02emu/g (18kOe) at room temperature. Both the UC luminescent and magnetic properties are closely related to the size of as-prepared products. These multifunctional β-NaGdF4 microrods would have potential applications in the fields such as solid-state lasers, lighting, displays, and magnetic resonance imaging (MRI), and so on.