Upconversion Fluorescence Properties Research Articles

One-pot green synthesis of optically pH-sensitive carbon dots with upconversion luminescence

One-pot fabrication of fluorescent carbon dots was facilely developed by directly heating ascorbic acid aqueous solution at 90 °C. The resulting carbon dots possess excitation, pH and polarity-dependent luminescence and upconversion fluorescence properties.

A Method to Improve the Up-Conversion Fluorescence of Polymer Modified NaYF<sub>4</sub>:Yb,Er(Tm) Nanocomposites

The modification of NaYF4:Yb,Er(Tm) nanoparticles synthesized in the presence of an ionic surfactant is critical to their application in biological fields for better solubility and biocompatibility. In this work, NaYF4:Yb,Er(Tm) was transformed from insoluble, inactive to hydrophilic, biocompatible via ligand exchange modification with polyacrylic acid (PAA). Ligand exchange was carried out at room temperature when a colloidal solution of NaYF4:Yb,Er(Tm) in tetrahydrofuran (THF) was treated with excess PAA. The PAA modified NaYF4:Yb,Er(Tm) nanoparticles got better surface properties but with declined inner up-conversion fluorescence. Generally, coating an analogous layer of material outside the core nanoparticles can improve the optical properties of the core. Accordingly, NaYF4:Yb,Er(Tm)/NaYF4 nanoparticles were synthesized before PAA modification to avoid the optical intensity decaying. The result of fluorescence test proved that the water soluble NaYF4:Yb,Er(Tm)/NaYF4/PAA nanocomposites had a sound up-conversion property compared with that of NaYF4:Yb,Er(Tm)/PAA. Furthermore, the up-conversion fluorescence property of the nanocomposite varied with the doping ratio of Er(Tm) to Yb and the possible mechanism for this change was also discussed.

Up-Conversion Fluorescence of Tm3+ and Gd3+ in Yb3+/Tm3+ Co-Doped Gd2O3 Nanocrystals

Through a co-precipitation method Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were synthesized. After sintered at 900 degrees C for 1 h in air, the as-prepared Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were converted into Gd2O3:20%Yb3+, 1% Tm3+ nanocrystals. Crystalline phases, sizes, and morphologies of the two samples were characterized by X-ray diffraction and field emission scanning electron microscope. The up-conversion (UC) fluorescence spectra of the Gd2O3:20%Yb3+, 1%Tm3+ nanocrystals were recorded by using a fluorescence spectrophotometer with a 980 nm continuous wave laser diode as excitation source. The nanocrystals not only present characteristic blue and ultraviolet (UV) UC emissions of activated Tm3+, but also show UV UC emissions of host Gd3+. The experimental study suggests that the excitation power has great effects on UC fluorescence properties and the energy transfer from Tm3+ to Gd3+ is very efficient.

Low-Temperature Flux Growth and Upconversion Fluorescence of the Idiomorphic Hexagonal-System NaYF4 and NaYF4:Ln (Ln = Yb, Er, Tm) Crystals

Idiomorphic NaYF4 and NaYF4:Ln (Ln = Yb, Er, Tm) crystals with upconversion fluorescence were successfully grown by the NaNO3 flux cooling method at a relatively low holding temperature. The grown NaYF4 and NaYF4:Ln crystals had a hexagonal prismatic form, and their well-developed surfaces were relatively flat. TEM images indicated that the NaYF4 crystals were of good crystallinity. Their size and shape were relatively uniform, and they were poorly aggregated. The crystal phase, form, and size depended on the growth temperature and the solute concentration. In contrast, the addition of dopant ions (Yb3+, Er3+, and Tm3+) did not affect the shape, morphology, or crystallinity of the flux-grown NaYF4:Ln crystals. Additionally, the upconversion fluorescence properties of NaYF4:Ln crystals were also dependent on the type and mixture ratio (i.e., starting composition) of the dopants. The green, orange, and blue upconversion fluorescences of NaYF4:10%Yb,1%Er, NaYF4:50%Yb,1%Er, and NaYF4:10%Yb,1%Tm crystals, resp...

Novel fabrication of NIR-vis upconversion NaYF4:Ln (Ln = Yb, Er, Tm) crystal layers by a flux coating method

High quality upconverting NaYF4:Ln (Ln = Yb, Er, Tm) crystal layers were successfully fabricated directly onto glass substrates at a relatively low temperature of 350 °C by a novel two-step flux coating method. First, mixed pastes of solute (NaF and YF3) and dopants (LnF3) were coated on glass substrates by simple bar-coating, and then flux pastes (NaNO3 or NaNO3–NaF) were coated onto the dopant-containing solute layer. After the two-step coating, raw material-coated substrates were heated at 350 or 400 °C in an electric furnace. To remove the remaining flux, the crystal layers were washed with warm water. Finally, high quality, nanotextured NaYF4:Ln crystal layers with good adhesion were directly grown onto the glass substrates. These crystal layers consisted of densely packed idiomorphic NaYF4:Ln crystals. In particular, individual NaYF4:Ln crystals were typically shaped as hexagonal prisms. The NaYF4:Ln crystal phases depended strongly on the heating conditions, i.e., temperature and time. The NaNO3 and NaNO3–NaF fluxes were effective for the growth of high-quality idiomorphic NaYF4:Ln crystals. Additionally, the upconversion fluorescence properties of NaYF4:Ln crystal layers were controlled by changing dopant types and ratios. The NaYF4:10%Yb,1%Er, NaYF4:50%Yb,1%Er, NaYF4:20%Yb,1%Tm and NaYbF4:1%Er crystal layers emitted green, orange, blue and red fluorescences, respectively, under 980 nm laser irradiation.

Synthesis and characterization of bifunctional magnetic–optical Fe3O4@SiO2@Y2O3 : Yb3+,Er3+ near-infrared-to-visible up-conversion nanoparticles

Bifunctional magnetic–optical Fe3O4@SiO2@Y2O3 : Yb3+,Er3+ near-infrared-to-visible up-conversion nanoparticles (UCNPs) with core–shell structures have been successfully fabricated by a facile layer-by-layer method. The presented materials were characterized by XRD, FTIR, TEM, fluorescence spectrophotometer, NMR Analyzer and SQUID MPMS. The results showed that the Fe3O4 cores were uniformly coated by SiO2 and Y2O3 : Yb3+,Er3+ layers. The amorphous silica used as the transition layer of UCNPs played an essential role in directing the structure of the composites. The inner Fe3O4 cores and the outer Y2O3 : Yb3+,Er3+ layers endow the composites with robust magnetic responsive properties and strong up-conversion fluorescent properties, which endow the nanoparticles with great potential applications in drug targeting, bioseparation and diagnostic analysis.

Obtaining Fluorescent Carbon Nanoparticles Directly from Active Carbon with One-step Ultrasonic Treatment

Water-soluble fluorescent carbon nanoparticles were synthesized directly from active carbon by a one-step hydrogen peroxide-assisted ultrasonic treatment. The carbon nanoparticles were characterized by transmission electron microscopy, optical fluorescent microscopy, fluorescent spectroscopy, fourier transform infrared spectroscopy and ultraviolet-visible spectrophotometer. The results showed that the surface of carbon nanoparticles was rich of hydroxyl groups resulting in high hydrophilicity. The carbon nanoparticles could emit bright and colorful photoluminescence covering the entire visible-to-near infrared spectral range. Furthermore, these carbon nanoparticles also had excellent up-conversion fluorescent properties.

One-step ultrasonic synthesis of water-soluble carbon nanoparticles with excellent photoluminescent properties

Monodispersed water-soluble fluorescent carbon nanoparticles (CNPs) were synthesized directly from glucose by a one-step alkali or acid assisted ultrasonic treatment. The CNPs were characterized by transmission electron microscopy, optical fluorescent microscopy, fluorescent spectrophotometry, fourier transform infrared spectrophotometry and ultraviolet-visible spectrophotometry. The results showed that the particle surfaces were rich in hydroxyl groups, giving them high hydrophilicity. The CNPs could emit bright and colorful photoluminescence covering the entire visible-to-near infrared (NIR) spectral range. Notably, the NIR emission of the CNPs could be obtained by NIR excitation. Furthermore, these CNPs also had excellent up-conversion fluorescent properties.

光谱学方法研究Tm3+离子的上转换发光影响因素

The effect of upconversion fluorescence properties in red laser pumping Tm3+ ions doped nanocrystals is studied with laser specroscopy.The upconversion efficiency caused by phonon energy is invesgated by changing the matrix and environment temperature of samples.The results show that suitable photon energy can improve the upconversion efficiency.Since the phonon energy depends on the sample temperature,the variation of the temperature can also influence the population rate of 3H4 level in Tm3+ doped low-phonon-energy crystal,resulting in the change of the fluorescence upconversion efficiency.

Fabrication of ordered magnetite-doped rare earth fluoride nanotube arrays by nanocrystal self-assembly

We describe a nanocrystal self-assembly method for the preparation of rare earth fluoride nanotube (ReF-NT) arrays and magnetite-doped rare earth fluoride nanotubes (Fe3O4-ReF-NTs) by using porous anodic aluminum oxide (AAO) as a hard template. The ReF-NTs can be simply prepared by the impregnation of α-NaYF4 nanocrystals doped with Yb and Er into the channels of the porous AAO and show a highly ordered nanotube array and excellent upconversion (UC) fluorescence properties. Similarly, the Fe3O4-ReF-NTs are obtained by the self-assembly of a mixture of Fe3O4 and Yb/Er doped α-NaYF4 nanocrystals in the AAO pore channels and have a uniform dispersion of magnetite nanocrystals on the rare earth fluoride tube matrix and possess multifunctional magnetic/UC properties. The diameter of these nanotubes can be varied from 60 nm to several micrometers depending on the pore size of the AAO template. The wall thickness can be increased from 10 to 35 nm by increasing the concentration of nanocrystals from 0.02 to 0.4 mmol/L, while the morphology of the nanotubes can be varied from small isolated domain structures to percolating domains and eventually to compact domains. A template-directed formation mechanism is proposed and the quantitative predictions of the model for such self-assembled nanocrystal spreading processes are demonstrated. Strong UC fluorescent emissions are realized for the nanotube arrays and multifunctional nanotubes with UC excitation in the near-infrared (NIR) region. A strong magnetic response of the multifunctional nanotubes is observed, which facilitates their easy separation from solution by magnetic decantation using a permanent magnet.

Frequency upconversion fluorescence studies of Er 3+/Yb 3+-codoped KNbO 3 phosphors

Different concentrations of Er 3+ and Yb 3+ ions-doped potassium niobate (K 0.9NbO 3:Yb (x)Er (0.1 − x) for x = 0, 0.01, 0.05, 0.09 and 0.1) polycrystalline powder phosphors were prepared by the conventional solid state reaction method and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Energy transfer and upconversion fluorescence properties of the Yb 3+ and Er 3+-codoped phosphors have been discussed. The XRD data has shown mono-phase for pure KNbO 3 while the doped samples represented additional phase formation. The SEM micrographs represented the rectangular crystal growth habit for the KNbO 3 phosphors when doped with 0.1 mol of Er 3+ ions. An intense green emission at 557 nm along with a red emission at 674 nm was observed when the doped samples were excited with 975 nm IR radiation. The upconversion mechanism has been discussed based on the excited state absorption and energy transfer mechanisms.

Three-Photon Absorption and Upconversion Fluorescence Properties of Series 1,3,4-Oxadiazole Derivatives

A newly synthesized 1,3,4-oxadiazole derivatives have been studied using a femtosecond Ti:sapphire laser system. The series molecules present strong three-photon absorption and frequency upconversion fluorescence at wavelengths from 1205nm to 1575nm. Furthermore, there is no proportional relationship between three-photon absorption cross sections and the chemical structure transformation from monomer, dimer to trimer. Effective charge-transfer distance by π-conjugation bonds may be the contributing factor. In the experimental design, the far-field intensity distribution of femtosecond laser beam has been taken into account. We give the optimized analytical solution of nonlinear transmission in a three-photon absorption (3PA) process when the incident beam has a Gaussian transverse spatial profile.

New transparent Er 3+-doped oxyfluoride tellurite glass ceramic with improved near infrared and up-conversion fluorescence properties

Transparent glass ceramics have been obtained by nucleation and growth of Y 2Te 6O 15 or Er 2Te 5O 13 cubic phase in a new Er 3+-doped oxyfluoride tellurite glass. Effect of heat treatment on absorption spectra, luminescence and up-conversion properties in the oxyfluoride tellurite glass has been investigated. With heat treatment the ultraviolet absorption edge red shifted evidently for the oxyfluoride telluride glass. The near infrared emission that corresponds to Er 3+: 4I 13/2 → 4I 15/2 can be significantly enhanced after heat treatment. Under 980 nm LD pumping, red and green up-conversion intensity of Er 3+ in the glass ceramic can be observed much stronger than that in the base glass.

Study of upconversion fluorescence property of novel Er 3+/Yb 3+ co-doped tellurite glasses

Er 3+/Yb 3+ co-doped TeO 2–B 2O 3–Nb 2O 5–ZnO (TBN) glasses were prepared. The absorption spectra and upconversion luminescence spectra of TBN glasses were measured and analyzed. The upconversion emission bands centered at 530, 546 and 658 nm were observed under the excitation at 975 nm, corresponding to the transitions of 2H 11/2 → 4I 15/2, 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2 respectively. The ratio of red emission to green emission increases with an increasing of Yb 3+ ions concentration. According to the quadratic dependence on excitation power, the possible upconversion mechanisms and processes were discussed.

Intense frequency upconversion fluorescence emission of Er 3+/Yb 3+-codoped oxychloride germanate glass

Structural and frequency upconversion fluorescence properties of Er 3+/Yb 3+-codoped oxychloride germanate glasses have been investigated. The Raman spectrum investigation indicates that PbCl 2 plays an important role in the formation of glass network and has an important influence on the upconversion luminescence. Intense green and red emissions centered at 525, 546 and 657 nm, corresponding to the transitions 2H 11/2 → 4I 15/2, 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2, respectively, were observed at room temperature. The possible upconversion mechanism was also estimated and evaluated. Intense upconversion luminescence indicates that Er 3+/Yb 3+-codoped oxychloride germanate glass is a promising laser material.

Green and red upconversion luminescence in ytterbium-sensitized erbrium-doped novel lead-free germanium–bismuth–lanthanum glass

Structural and infrared-to-visible upconversion fluorescence properties in ytterbium-sensitized erbrium-doped novel lead-free germanium–bismuth–lanthanum glass have been studied. The structure of lead-free germanium–bismuth–lanthanum glass was investigated by peak-deconvolution of Raman spectrum, and the structural information was obtained from the peak wavenumbers. Intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions 2H 11/2 → 4I 15/2, 4S 3/2 → 4I 15/2, and 4F 9/2 → 4I 15/2, respectively, were observed at room temperature. The quadratic dependence of the 525, 546, and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm excitation. This novel lead-free germanium–bismuth–lanthanum glass with low maximum phonon energy (∼ 751 cm −1) can be used as potential host material for upconversion lasers.

Optical transitions of Er3+ and Yb3+ ions in novel oxyfluoride bismuth–germanium glass: Observation of up-conversion

Er3+/Yb3+-codoped novel oxyfluoride bismuth–germanium glass was prepared and its up-conversion fluorescence property under 975 nm excitation has been studied. Intense green and weak red emissions centered at 525, 546, and 657 nm, corresponding to the transitions 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2, respectively, were observed at room temperature. The possible up-conversion mechanism was also evaluated. The optimal Yb3+–Er3+ concentration ratio is found based on the direct lifetime measurements of excited levels for Er3+ ion. The structure of this novel oxyfluoride bismuth–germanium glass has been investigated by peak-deconvolution of FT-Raman spectrum, and the structural information was obtained from the peak wavenumbers. This novel oxyfluoride bismuth–germanium glass with relatively lower maximum phonon energy (∼731 cm−1) can be used as potential host material for up-conversion lasers.

Structural and Upconversion Fluorescence Properties ofEr3+/Yb3+-Codoped Lead-Free Germanium-Bismuth Glass

We study the structural and infrared-to-visibleupconversion fluorescence properties of Er3+/Yb3+-codopedlead-free germanium-bismuth glass. The structure of lead-freegermanium–bismuth–lanthanum glass is investigated by peak-deconvolutionof Raman spectroscopy. Intense green and red emissions centred at 525,546, and 657 nm, corresponding to the transitions 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2, respectively, are observed at room temperature. Thequadratic dependence of the 525, 546, and 657 nm emissions onexcitation power indicates that a two-photon absorption process occursunder 975 nm excitation.

Intense upconversion luminescence in ytterbium-sensitized thulium-doped novel oxychloride bismuth–germanium glass

Structural and up-conversion fluorescence properties in ytterbium-sensitized thulium-doped novel oxychloride bismuth–germanium glass have been studied. The structure of novel bismuth–germanium glass was investigated by peak-deconvolution of Raman spectrum, and the structural information was obtained from the peak wave numbers. The Raman spectrum investigation indicates that PbCl 2 plays an important role in the formation of glass network, and has an important influence on the up-conversion luminescence. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions 1G 4→ 3H 6 and 1G 4→ 3H 4, respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. This novel oxychloride bismuth–germanium glass with low maximum phonon energy (∼730 cm −1) can be used as potential host material for up-conversion lasers.

Frequency Upconversion Fluorescence Emission ofEr3+-Doped Oxychloride Germanate Glass

Frequency upconversion fluorescence property of Er3+-dopedoxychloride germanate glass is investigated. Intense green and redemissions centred at 525, 546, and 657 nm, corresponding to thetransitions 2H11/2→4I15/2,4S3/2→4I15/2, and 4F9/2→4I15/2,respectively, were simultaneously observed at room temperature. Thequadratic dependence of the 525, 546, and 657 nm emissions onexcitation power indicates that a two-photon absorption process occursunder 975 nm laser diode (LD) excitation. The Raman spectruminvestigation indicates that oxychloride germanate glass has the maximumphonon energy at ~805 cm−1. The thermal stability of thisoxychloride germanate glass is evaluated by differential scanningcalorimetry, and thermal stability factor ΔT (ΔT = Tx−Tg) is 187 degrees C. Intense upconversion luminescence and goodthermal stability indicate that Er3+-doped oxychloride germanateglass is a promising upconversion laser material.