Uniform Upconversion Research Articles

Uniform upconversion film with large area prepared by improved confined-space synthesis method

We prepared uniform and large-scaled upconversion films with the greatly enhanced fluorescence using a modified confined-space synthesis method. The diffusion of NaYF4:20%Yb, 0.5%Tm precursors into the confined-space that was constructed by three overlapping silica glass substrates was facilitated by designing open channels into the upper substrate. A uniform upconversion film with an area of 4 cm × 4 cm was prepared, which can transfer the near-infrared light of 980 nm into 346, 361, 452, 475, 646, and 802 nm. In comparison with the film prepared without open channels, the fluorescence intensity of the upconversion film here was increased by 20 times.

Controlled Synthesis of Uniform and Monodisperse Upconversion Core/Mesoporous Silica Shell Nanocomposites for Bimodal Imaging

Here we report the design and controlled synthesis of monodisperse and precisely size-controllable UCNP@mSiO(2) nanocomposites smaller than 50 nm by directly coating a mesoporous silica shell (mSiO(2)) on upconversion nanocrystals NaYF(4):Tm/Yb/Gd (UCNPs), which can be used as near-infrared fluorescence and magnetic resonance imaging (MRI) agents and a platform for drug delivery as well. Some key steps such as transferring hydrophobic UCNPs to the water phase by using cetyltrimethylammonium bromide (CTAB), removal of the excess amount of CTAB, and temperature-controlled ultrasonication treatment should be adopted and carefully monitored to obtain uniform upconversion core/mesoporous silica shell nanocomposites. The excellent performance of the core-shell-structured nanocomposite in near-infrared fluorescence and magnetic resonance imaging was also demonstrated.

General Synthesis Route to Fabricate Uniform Upconversion Luminescent Gadolinium Oxide Hollow Spheres

Uniform upconversion luminescent gadolinium oxide hollow spheres were successfully synthesized via a homogeneous precipitation method with carbon spheres as template followed by a calcination process. During the annealing process, the carbon spheres template can be effectively removed and the amorphous precursor has converted to crystalline Gd2O3, which can be confirmed by the XRD and TG-DSC analysis. SEM and TEM images indicate that the Gd2O3 hollow spheres with diameters of 300-400 nm are uniform in size and distribution. The rare earth activator ions Ln3+-doped Gd2O3 hollow spheres exhibit intense upconversion luminescence with different colors under 980 nm light excitation, which may find potential applications in the fields such as drug delivery or biological labeling. Moreover, the upconversion luminescent mechanisms of the hollow spherical phosphors were investigated in detail.

Uniform Alkaline Earth Fluoride Nanocrystals with Diverse Shapes Grown from Thermolysis of Metal Trifluoroacetates in Hot Surfactant Solutions

Uniform alkaline earth metal fluoride MF2 (M = Mg, Ca, and Sr) nanocrystals with various shapes (tetragonal MgF2 nanoneedle-constructed 3D networks; cubic CaF2 nanoplates and nanopolyhedra; cubic SrF2 nanoplates and nanowires) have been synthesized from the thermolysis of alkaline earth metal trifluoroacetate (M(CF3COO)2) in hot surfactant solutions (oleic acid, oleylamine, and 1-octadecene). The MF2 nanocrystals were formed by the controlled fluorination of the M−O bond into the M−F bond at the nucleation stage and subsequent growth process. For phase-pure MF2 nanocrystals, the growth of shape-selective MF2 nanocrystals was likely due to the template direction of micellar structures formed by self-assembly of capping ligands and the so-called “Ostwald ripening” process. With the developed synthetic strategy, the uniform upconversion SrF2:Yb,Er and core/shell SrF2:Yb,Er@SrF2 nanocrystals were also obtained. The core/shell-structured nanocrystals exhibited enhanced emission intensity and saturation power w...

Model showing effect of impurity sub-lattice topologyon upconversion in Er 3+ -doped glasses

Monte Carlo methods are used to simulate a spatial model of uniform upconversion and commensurate excited-state depletion in high-concentration Er3+-doped solids. It is found that the topology of the impurity sublattice affects the value of the upconversion coefficient, a result in accord with recent measurements on samples prepared with identical host compositions and ion concentrations.

Numerical analysis of Yb3+-sensitised, Er3+-doped, fibre-ring laser

The performance of a Yb/sup 3+/-sensitised Er/sup 3+/-doped, continuous-wave, fibre-ring laser is analysed using a comprehensive numerical model. The model is based on iterative solution propagation-rate equations and takes account realistic refractive-index profile and Er/sup 3+//Yb/sup 3+/-doping distribution function, uniform upconversion from the /sup 4/I/sub 13/2/ erbium level and propagation of amplified spontaneous emission in the pump wavelength range. The dependence of output power on active fibre length, input pump power and output coupling ratio has been investigated. The analysis has shown that the laser can be tuned in the range 1525 nm - 1610 nm. The calculated ring-laser characteristics have been found in quantitative agreement with the experimentally obtained data.

Uniform upconversion in high-concentration Er^3+-doped soda lime silicate and aluminosilicate glasses

Uniform upconversion in erbium-doped silicate glasses is investigated as a function of glass composition, concentration, and fabrication method. Comparisons of upconversion coefficients are made among soda lime silicate and aluminosilicate bulk glasses and soda lime silicate waveguides. Comparisons are also made with studies performed by other researchers. The results indicate that both the composition and the preparation method of the glass affect the value of the upconversion coefficient, with as much as a factor-of-4 variation observed at fixed Er(3+) concentration. Values of the upconversion coefficient are found to be consistent with the Förster-Dexter microscopic model.

Theoretical analysis of the dynamic behavior of highly-efficient erbium/ytterbium codoped fiber lasers

A numerical study of the transient behavior of single-mode Er/sup 3+//Yb/sup 3+/ codoped fiber lasers is presented. The model, based on propagation-rate equations, includes both uniform up-conversion from the /sup 4/I/sub 15/2/ and /sup 4/I/sub 9/2/ erbium levels and the pair-induced energy transfer process from ytterbium to erbium. We show that neglecting the r dependence of the operating fiber laser parameters allows accurate simulation results at minimum numerical effort. Using this numerical model, we characterize the laser relaxation oscillations and the effect of ytterbium on the dynamic behavior and stability with respect to fluctuations of the pump power. Our results confirm that the presence of Yb/sup 3+/ enhances the efficiency of the laser and show that its stability is also significantly improved.

Modeling of highly-efficient grating-feedback and Fabry-Perot Er/sup 3+/-Yb/sup 3+/ co-doped fiber lasers

The continuous wave operations of highly-efficient Er/sup 3+//Yb/sup 3+/ co-doped fiber lasers pumped at 980 nm are numerically analyzed. The model, based on propagation-rate equations, includes uniform upconversion from the /sup 4/I/sub 13/2/ and /sup 4/I/sub 11/2/ erbium levels and a pair-induced energy transfer process from Yb/sup 3+/ to Er/sup 3+/; it allows the description of both single-mode and multimode laser operations. Numerical results show that slope efficiencies close to the quantum limit, with threshold pump powers of few mW, can be achieved in short single-frequency fiber lasers using grating Bragg reflectors. Moreover, we demonstrate the possibility of performing equispaced multiwavelength laser emissions in high-concentration Fabry-Perot fiber microlasers.

1.7 μm excited state absorption measurement in erbium-doped glasses

We have measured the complete 1.7 μm excited state absorption (ESA) spectrum in erbium-doped glasses. The spectrum is obtained by measuring the gain of an erbium-doped waveguide in the 1400–1800 nm region. Using the measured spectra, we estimate the 1.5 μm uniform upconversion rate by calculating the spectral overlap between the 1.5 μm emission and 1.7 μm ESA cross sections. The technique is applied to erbium-doped, ion-exchangeable silicate glasses yielding upconversion constants in the range of 1–10×10−18 cm3/s.

Finite-element analysis of single-frequency silica-based Er3+-Yb3+ co-doped waveguide lasers

Continuous wave laser operations of silica-based Er/sup 3+/-Yb/sup 3+/ co-doped waveguides have been numerically analyzed by means of a finite-element method. The theoretical model, based on propagation-rate equations, describes uniform upconversion by a dipole-dipole interaction between Er/sup 3+/ ions, and includes a pair-induced energy transfer process from Yb/sup 3+/-Er/sup 3+/ Numerical results show that single-frequency operation with slope efficiency higher than 50% and threshold pump powers of few mW can be achieved in short and heavily doped waveguides equipped with input dielectric mirrors and output distributed Bragg reflectors. >

The effect of pair-induced energy transfer on the performance of silica waveguide amplifiers with high Er/sup 3+//Yb/sup 3+/ concentrations

High-concentration Er/sup 3+//Yb/sup 3+/ co-doped silica waveguide amplifiers are numerically analyzed. With optimized rare-earth concentrations the effect of Er/sup 3+//Er/sup 3+/ ion-pairs can be neglected and each Er/sup 3+/ ion can be assumed to be paired only to the surrounding Yb/sup 3+/ ions. The rate-equations model includes uniform upconversion mechanisms from /sup 4/I/sub 13/2/ and /sup 4/I/sub 11/2/ erbium levels and an Yb/sup 3+/ to Er/sup 3+/ pair-induced energy transfer process. Numerical results demonstrate the possibility of fabricating short- and high-gain integrated optical amplifiers; it is shown that net gain as high as 3 dB/cm can be obtained. >

Modelling of uniform and pair-induced upconversion mechanisms in high-concentration erbium-doped silica waveguides

Effects of high concentration and clustering on the performance of erbium-doped silica waveguide amplifiers are numerically investigated. The model, based on propagation-rate equations of a laser system containing isolated ions and ion-pairs, is numerically solved by combining Runge-Kutta and full-vectorial finite-element methods; it allows the description of both uniform and pair-induced upconversion mechanisms. Numerical results show that cooperative upconversion processes seriously deteriorate amplifier performance at high erbium concentration. Moreover, we show that only the detrimental effect due to uniform upconversion can be reduced by a careful design of waveguide geometry and refractive index profile; performance degradation due to clustering may only be overcome by reducing the fraction of ions in pair using suitable codopants. The proposed model is validated with published experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>