Na(Y1.5 Na0.5)F6 single-crystal nanorods as multicolor luminescent materials

A facile wet chemical synthesis method was used to prepare a range of single-crystal Na(Y1.5 Na0.5)F6 nanorods with controllable aspect ratios. Their novel multicolor upconversion (UC) fluorescence has been successfully realized by doping Yb3+/Er3+ (green) and Yb3+/Tm3+ (blue) ion pairs. When doped with Eu3+ and Tb3+ ions, the strong red and green downconversion (DC) fluorescence has also been observed, respectively. Being covered with oleic acids, these luminescent nanorods have been transparently dispersed in nonpolar solvent. For their unique luminescence and controllable morphology and surface properties, these nanorods may find great applications in the fields of color displays, biolabels, light-emitting diodes (LEDs), optical storage, optoelectronics, anticounterfeiting, and solid-state lasers.     

Spectral characterization of Yb-doped silica layers for high power laser applications

Thick silica layers, doped with rare-earth elements are required as active media for high power waveguide lasers and amplifiers. In this work, Yb/Al-codoped silica particles were deposited on pure silica wafers, followed by high temperature sintering and post-sinter laser annealing treatment. The optical properties of the layers were monitored at different stages of the process using transmission spectrometry in the near IR to UV range, micro-Raman spectroscopy, fluorescence spectrum, and decay measurements. Evolution of the Yb³⁺ ion fluorescence and stabilization of the Si:O bonds as a result of the sintering process were observed.Measurements of 30 μm thick layers showed high Yb absorption of 500 dB/m at 980 nm. The fluorescence lifetime was close to 1 ms and the propagation loss was less than 20 dB/m at 633 nm, currently limited by the measurement system. The results show that a potential material for high power applications has been achieved.     

Hydrothermal derived nanostructure rare earth (Er,Yb)-doped ZnO: structural,optical and electrical properties

The structural, optical and electrical properties of undoped and rare-earth (Er, Yb) doped zinc oxide (ZnO) nanopowder samples synthesized by hydrothermal method were investigated. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy. The optical properties of undoped and rare-earth (Er, Yb) doped ZnO were carried out with UV–visible diffuse reflectance spectroscopy techniques. XRD results reveal that Yb and Er doped ZnO nanopowders have single phase hexagonal (Wurtzite) structure without any impurities. SEM analysis indicate that dopants with different radii affected the surface morphology of ZnO nanostructures. The optical band gap of all samples were calculated from UV–Vis diffuse reflectance spectroscopy data. We have obtained band gap values of undoped, Er and Yb doped ZnO as 3.24, 3.23, 3.22 eV, respectively. Electrical characterization of the samples were made in the 280–350 K temperature range using Van der Pauw method based on Hall effect measurement. The carrier concentrations decreased for both Er and Yb doping while the Hall mobility and electrical resistivity increased with Yb, Er doping compared to undoped ZnO nanopowder at room temperature. The temperature dependent resistivity measurements of Er doped ZnO showed a metal–semiconductor transition at about 295 K, while Yb doped ZnO showed characteristic semiconductor behavior.     

Laser stimulated bistability in the Yb doped Nd gallate

An effect similar to the one observed in the case of Nd₃BWO₉:Yb was discovered during investigation of the emission excited at 0.77 μm 10 ns pulsed SHG of the Er³⁺ glass lasers in the Yb doped Nd gallate (NdGaO₃:Yb). The laser beam was used simultaneously for photo thermal heating as well as for the photo excitation. We have discovered an enhancement of the intensities of the Nd³⁺ emission lines (at about 1060 nm) and decrease of the intensity of the Yb³⁺ lines at 975, and 994 nm. The photo treatment of the 2 mm thick samples were performed at temperature about 10 K. Such optically stimulated bistability may be caused by photo thermal mechanisms, and principal role of the IR reflected modes at 450 cm^− 1 is shown. The latter are determined by PL of Nd → Yb transfer or Yb → Nd back transfer processes. The observed phenomenon may be used for production of optically operated switchers. The PL spectrum possesses more complicated structure with respect to other hosts, which may reflect a different local surrounding of the incorporated ions.     

Synthesis of Brightly PEGylated Luminescent Magnetic Upconversion Nanophosphors for Deep Tissue and Dual MRI Imaging

A method is developed to fabricate monodispersed biocompatible Yb/Er or Yb/Tm doped β‐NaGdF₄ upconversion phosphors using polyelectrolytes to prevent irreversible particle aggregation during conversion of the precursor, Gd₂O(CO₃)₂?H₂O:Yb/Er or Yb/Tm, to β‐NaGdF₄:Yb/Er or Yb/Tm. The polyelectrolyte on the outer surface of nanophosphors also provided an amine tag for PEGylation. This method is also employed to fabricate PEGylated magnetic upconversion phosphors with Fe₃O₄ as the core and β‐NaGdF₄ as a shell. These magnetic upconversion nanophosphors have relatively high saturation magnetization (7.0 emu g^?1) and magnetic susceptibility (1.7 × 10^?2 emu g^?1 Oe^?1), providing them with large magnetophoretic mobilities. The magnetic properties for separation and controlled release in flow, their optical properties for cell labeling, deep tissue imaging, and their T₁‐ and T₂‐weighted magnetic resonance imaging (MRI) relaxivities are studied. The magnetic upconversion phosphors display both strong magnetophoresis, dual MRI imaging (r₁ = 2.9 mM^?1 s^?1, r₂ = 204 mM^?1 s^?1), and bright luminescence under 1 cm chicken breast tissue.     

Structural, magnetic and optical behavior of pristine and Yb doped CoWO4 nanostructure

Nanocrystalline pure and Yb doped CoWO₄ nanostructures were synthesized successfully by single step chemical precipitation technique. The prepared sample was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal analysis (TGA). XRD pattern reveals the pure and doped CoWO₄ nanoparticles belongs to the monoclinic structure with the space group of P_2/c. Electron microscopy studies clearly evidence the formation of round edged nanocubes with an average particle size of 60–80 nm, emerges in the polycrystalline nature. UV–Visible absorption spectra of Yb³⁺ doped CoWO₄ nanocrystals shows a strong absorption peak at 278 nm due to CoWO₄ metal to ligand charge transfer within the [WO₆]^6? complex. Photoluminescence spectra of pure and doped CoWO₄ nanostructures substantiate the effect of Yb on the wolframite structure and its response for optical behavior. These results suggest that the addition of Yb into the Co-site on CoWO₄ has no significant contribution for luminescent enhancement when compared to pure one up to 5 % Yb concentration. Typical magnetization curve shows the mixed ferromagnetic and diamagnetic transition of CoWO₄ with respect to the Yb doping concentration.     

Cathodoluminescence study of CdTe crystals doped with Bi and Bi:Yb

Bi doped and Bi and Yb codoped CdTe crystals grown by the Bridgman method have been characterized by cathodoluminescence (CL) in the scanning electron microscope. CL images show a dense network of highly decorated grain boundaries in the Bi doped samples and dopant striations in the codoped crystals, attributed to the presence of Yb. Bi contributes to the appearance of the A luminescence band at 1.43 eV. The influence of Yb dopant on the CL spectra is discussed.     

Investigation of continuous-wave and Q-switched microchip laser characteristics of Yb:YAG ceramics and crystals

Continuous-wave and passively Q-switched microchip laser performance of Yb:YAG ceramics and single-crystals was investigated. Highly efficient continuous-wave Yb:YAG laser performance was observed at 1030 nm and 1049 nm for both Yb:YAG ceramics and crystals with different transmissions of output couplers. The laser performance of Yb:YAG ceramic is comparable to that of Yb:YAG single crystal. Meanwhile, the laser performance of laser-diode pumped Yb:YAG/Cr⁴⁺:YAG all-ceramics- and all-crystals-combination passively Q-switched microchip lasers were investigated. Sub-nanosecond laser pulses with peak power over 150 kW were obtained with different Yb:YAG/Cr⁴⁺:YAG combinations. Linearly polarized laser was observed in Yb:YAG/Cr⁴⁺:YAG all-crystals combination and circular polarized laser was obtained in Yb:YAG/Cr⁴⁺:YAG all-ceramics combination. The best laser performance was obtained with Yb:YAG/Cr⁴⁺:YAG all-crystals combination.     

Structural and luminescence properties of Ho(3+)/Yb(3+)-doped Lu3Ga5O12 nano-garnets for phosphor applications

Lu3Ga5O12 nano-garnet powders doped with Ho(3+)/Yb(3+) ions have been prepared using a citrate sol-gel technique. The structural and morphological properties have been investigated by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The materials are found to exist in single phase of cubic garnet structure with an average particle size of around 45 nm. The Ho(3+)/Yb(3+)-doped Lu3Ga5O12 nano-garnet powders give rise to an intense green and weak red emission of Ho3+ ions under 457.5 nm direct excitation. Moreover, when the Yb3+ ions are excited at 950 nm a very bright green luminescence of the Ho3+ ions is observed by the naked eyes even for such low laser power as 10 mW and the intensity of the red emission have been increased compared to that found under direct excitation of the Ho3+ ions. The power dependency and dynamics of the infrared-to-visible upconverted luminescence confirm the existence of different two-photon energy transfer processes. All these results have been compared with those obtained for other garnets doped with similar lanthanide ions which suggest that the Lu3Ga5O12 nano-garnets are potential materials for light emitting devices.     

Effects of fine metal oxide particle dopant on the acoustic properties of silicone rubber lens for medical array probe

The effects of fine metal oxide particles, particularly those of high-density elements (7.7 to 9.7 x 10(3) kg/m3), on the acoustic properties of silicone rubber have been investigated in order to develop an acoustic lens with a low acoustic attenuation. Silicone rubber doped with Yb2O3 powder having nanoparticle size of 16 nm showed a lower acoustic attenuation than silicone rubber doped with powders of CeO2, Bi2O3, Lu2O3 and HfO2. The silicone rubber doped with Yb2O3 powder showed a sound speed of 0.88 km/s, an acoustic impedance of 1.35 x 10(6) kg/m2s, an acoustic attenuation of 0.93 dB/mmMHz, and a Shore A hardness of 55 at 37 degrees C. Although typical silicone rubber doped with SiO2 (2.6 x 10(3) kg/m3) shows a sound speed of about 1.00 km/s, heavy metal oxide particles decreased the sound velocities to lower than 0.93 km/s. Therefore, an acoustic lens of silicone rubber doped with Yb2O3 powder provides increased sensitivity because it realizes a thinner acoustic lens than is conventionally used due to its low sound speed. Moreover, it has an advantage in that a focus point is not changed when the acoustic lens is pressed to a human body due to its reasonable hardness.     

Rare-earth ion doped TeO2 and GeO2 glasses as laser materials

Germanium oxide (GeO₂) and tellurium oxide (TeO₂) based glasses are classed as the heavy metal oxide glasses, with phonon energies ranging between 740 cm^?1 and 880 cm^?1. These two types of glasses exhibit unique combinations of optical and spectroscopic properties, together with their attractive environmental resistance and mechanical properties. Engineering such a combination of structural, optical and spectroscopic properties is only feasible as a result of structural variability in these two types of glasses, since more than one structural units (TeO₄ bi-pyramid, TeO₃ trigonal pyramid, and TeO_3+δ polyhedra) in tellurite and (GeO₄ tetrahedron, GeO₃ octahedron) in GeO₂ based glasses may exist, depending on composition. The presence of multiple structural moities creates a range of dipole environments which is ideal for engineering broad spectral bandwidth rare-earth ion doped photonic device materials, suitable for laser and amplifier devices. Tellurite glasses were discovered in 1952, but remained virtually unknown to materials and device engineers until 1994 when unusual spectroscopic, nonlinear and dispersion properties of alkali and alkaline earth modified tellurite glasses and fibres were reported. Detailed spectroscopic analysis of Pr³⁺, Nd³⁺, Er³⁺, and Tm³⁺ doped tellurite glasses revealed its potential for laser and amplifier devices for optical communication wavelengths. This review summarises the thermal and viscosity properties of tellurite and germanate glasses for fibre fabrication and compares the linear loss for near and mid-IR device engineering. The aspects of glass preform fabrication for fibre engineering is discussed by emphasising the raw materials processing with casting of preforms and fibre fabrication. The spectroscopic properties of tellurite and germanate glasses have been analysed with special emphasis on oscillator strength and radiative rate characteristics for visible, near IR and mid-IR emission. The review also compares the latest results in the engineering of lasers and amplifiers, based on fibres for optical communication and mid-IR. The achievements in the areas of near-IR waveguide and mid-IR bulk glass, fibre, and waveguide lasers are discussed. The latest landmark results in mode-locked 2 μm bulk glass lasers sets the precedence for engineering nonlinear and other laser devices for accessing the inaccessible parts of the mid-IR spectrum and discovering new applications for the future.     

Ion-exchanged waveguide lasers in Er3+/Yb3+ codoped silicate glass

We investigated an Er(3+)/Yb(3+) codoped silicate glass as a host material for waveguide lasers operating near 1.5 mum. Spectroscopic properties of the glass are reported. Waveguide lasers were fabricated by K(+)-ion exchange from a nitrate melt. The waveguides support a single transverse mode at 1.5 mum. An investigation of the laser performance as a function of the Yb:Er ratio was performed, indicating an optimal ratio of approximately 5:1. Slope efficiencies of as great as 6.5% and output powers as high as 19.6 mW at 1.54 mum were realized. The experimental results are compared with a waveguide laser model that is used to extract the Er(3+) upconversion coefficients and the Yb(3+)-Er(3+) cross-relaxation coefficients. The results indicate the possibility of obtaining high-performance waveguide lasers from a durable silicate host glass.     

One-step synthesis of highly water-soluble LaF(3):Ln(3+) nanocrystals in methanol without using any ligands

Water-soluble infrared-to-visible fluorescent LaF(3) nanocrystals doped with different lanthanide ions (Er(3+)/Yb(3+), Eu(3+), Nd(3+), Tb(3+)) have been synthesized in methanol without using any ligands. These nanocrystals are easily dispersed in water, producing a transparent colloidal solution. The colloids of the Er(3+)/Yb(3+), Eu(3+), Nd(3+), Tb(3+) doped nanocrystals exhibit strong luminescence in the visible and near-infrared spectral regions.     

A Tunable Visible Solid State Laser

Abstract

Laser operation and radiative properties of organically doped porous sol-gel silica have been studied using a range of cavities. Measurements of diffusion, distribution and long term photostability of dopant dye molecules are described. Laser oscillation at wavelengths of between 360 and 630 nm are reported. This represents a substantial increase over the range previously reported for organic dye doped silica lasers. In a Littrow configuration a tuning range of 60 nm and a conversion efficiency of 16% have been observed. A linewidth of <0·05 nm has been obtained using a grazing incidence cavity.     

Analysis and Performance of 2·7 μm Er3+ Fibre Laser Amplifiers and Oscillators

Abstract

A mathematical model is described which estimates the performance of erbium doped fibre lasers and amplifiers at 1·5 μm or at 2·7 μm. The model has shown good agreement with experimental results and has been used to optimize the configuration of new systems. Continuous wave laser action has been demonstrated at λ = 2·7 μm in an Er³⁺ doped multi-mode fluorozirconate fibre laser, pumped by an 800 nm laser diode.     

Synthesis of ternary fluorides BaCaLn2F10 - Eu2+ luminescence in BaCaLu2F10

A new family of the ternary BaCaLn₂F₁₀ (Ln=Lu, Yb, Tm, Er, Ho, Dy) system has been prepared. Emission and excitation spectra of Eu²⁺ doped BaCaLu₂F₁₀ are presented and discussed.     

Waveguiding properties in Yb:YAG crystals implanted with protons and carbon ions

We report the fabrication and analysis of optical waveguides in Yb:YAG crystals using either proton or carbon ion implantation. Planar waveguides were obtained by implanting the whole surface of the crystals. Channel waveguides were defined using an electroformed mask with apertures of 10, 15, and 20 micrometers in width. The waveguiding properties of the structures were analyzed, showing good light confinement based on the transversal mode distribution and optical transmission measurements. The spectroscopic properties of the Yb ions in the YAG host are preserved after the implantation process, which demonstrates the potential of this technique for tailoring microcomponents for integrated optics applications. In particular, the Yb:YAG waveguides have the potential to operate as miniature lasers.     

Spectroscopic characterization of red perylimide/surfactant nanocomposites

Novel photoluminescent materials formed by some selected surfactants, metal derivatives of bis(2-ethylhexyl) sulfosuccinate (M(AOT) _n ; M = Na⁺, Co²⁺, Er³⁺ and Yb³⁺), bis(2-ethylhexyl) amine (BEEA), bis(2-ethylhexy1) phosphoric acid (HDEHP) and a 1:1 BEEA/HDEHP mixture, doped with the red perylimide (ROT-300) have been prepared, and their optical properties have been tested by absorption spectroscopy and steady state and time-resolved fluorescence. Experimental results show spectral shifts of the typical ROT-300 absorption and fluorescence bands with respect to that in apolar solvent medium. Data analysis leads consistently to attribute this feature mainly to the freezing of the diffusive movement of the dye molecules confined in the nanodomains of the surfactant liquid crystals, whilst minor effects can be due to interaction with the surfactant polar groups. Potentialities of these novel luminescent nanostructured composites as dye lasers, optical amplifiers and solar concentrators have been highlighted. In particular, under optical pumping using a pulse laser, amplified spontaneous fluorescence emission of the ROT-300/HDEHP system above an excitation energy threshold value of about 725 mJ cm⁻² was observed.     

Structural and spectroscopic characterization of Yb doped Lu2O3 transparent ceramics

Yb³⁺ doped Lu₂O₃ transparent ceramics were fabricated by the solid-state reaction method and sintered in H₂ atmosphere. Structural and spectroscopic properties of Yb:Lu₂O₃ ceramics were studied. The Yb:Lu₂O₃ ceramic structure, and the lattice parameter are refined with the Rietveld method. Yb:Lu₂O₃ has broad absorption and emission bands with a long fluorescence lifetime (1.31 ms). The energy level diagram is calculated based on the absorption and emission spectra, Yb³⁺ in Lu₂O₃ ceramics exhibits a big splitting energy of the ²F_7/2 ground state (1023 cm⁻¹). Furthermore, the gain cross-section (σ_g) is estimated with different β values.     

EPR properties of KY(WO4)2 single crystals weakly doped with Er,Yb and Nd

Well oriented KY(WO₄)₂ single crystal weakly doped simultaneously with Er, Yb and Nd have been investigated using EPR technique. Angular dependencies of the EPR lines clearly confirm C₂ symmetry of all: Er³⁺, Yb³⁺ and Nd³⁺ dopants. Basic parameters of the spin Hamiltonian, including Zeeman and hyperfine terms (g and A matrices) as well the spatial orientation between principal axes system and crystallographic axes system were determined.