Dependence of Er3+ blue up-conversion on TiO2 contents in SiO2–TiO2 sol–gel powder

The TiO₂ content was changed from low to high concentration (5–70% molar) in binary erbium doped SiO₂–TiO₂ powder samples produced by the sol–gel method. Three pumping wavelengths 532, 979 and 1532 nm, were used to study the blue up-conversion emission and its dependency on the titanium dioxide content. Two erbium concentrations were considered, at 2% and 10% molar. The titanium dioxide content affects the cluster formation, so at low erbium concentration and pumping at 532 nm, the blue and red emissions were enhanced as the TiO₂ content increased. However, at high erbium concentration and exciting at 979 and 1532 nm those emissions were quenched as the titanium dioxide was increased.     

Efficient upconversion-pumped continuous wave Er3+:LiLuF4 lasers

We report on detailed spectroscopic investigations and efficient visible upconversion laser operation of Er³⁺:LiLuF₄. This material allows for efficient resonant excited-state-absorption (ESA) pumping at 974 nm. Under spectroscopic conditions without external feedback, ESA at the laser wavelength of 552 nm prevails stimulated emission. Under lasing conditions in a resonant cavity, the high intracavity photon density bleaches the ESA at 552 nm, allowing for efficient cw laser operation.We obtained the highest output power of any room-temperature crystalline upconversion laser. The laser achieves a cw output power of 774 mW at a slope efficiency of 19% with respect to the incident pump power delivered by an optically-pumped semiconductor laser. The absorption efficiency of the pump radiation is estimated to be below 50%.To exploit the high confinement in waveguides for this laser, we employed femtosecond-laser pulses to inscribe a cladding of parallel tracks of modified material into Er³⁺:LiLuF₄ crystals. The core material allows for low-loss waveguiding at pump and laser wavelengths. Under Ti:sapphire pumping at 974 nm, the first crystalline upconversion waveguide laser has been realized. We obtained waveguide-laser operation with up to 10 mW of output power at 553 nm.     

Luminescent properties and energy transfer processes of co-doped Yb–Er poly-crystalline YAG matrix

A poly-crystalline YAG matrix was obtained through the precipitation method; this matrix was single and co-doped with ytterbium and erbium ions, i.e., Yb:YAG, Er:YAG and Yb,Er:YAG. It is found that the measured luminescent properties are similar to those reported for a mono-crystal YAG matrix. In addition, by studying the energy transfer processes in co-doped samples, it is shown that at high erbium concentrations the red emission is enhanced through an up-conversion process that takes place from the ⁴I_13/2 to the ⁴F_9/2 state of erbium ions. This enhanced red emission becomes comparable in intensity to the observed green emission and occurs by pumping at 800 nm through a back energy transfer process.     

Polarized spectral properties of Sm3+:LiLuF4 crystal for visible laser application

A Sm³⁺-doped LiLuF₄ single crystal was grown by the vertical Bridgman–Stockbarge technique. Polarized absorption spectra, polarized fluorescence spectra, and fluorescence lifetime of the Sm³⁺:LiLuF₄ crystal were recorded at room temperature. Based on the Judd–Ofelt theory, spectral parameters of the Sm³⁺:LiLuF₄ crystal were calculated. Emission cross sections for the ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, and 11/2) transitions with special interest for visible laser application were obtained by the Füchtbauer–Ladenburg formula. The results indicate that the Sm³⁺:LiLuF₄ crystal may be a potential laser gain medium operating in visible region pumped by diode lasers around 401 nm.     

Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

Influence of Mn<Superscript>2+</Superscript> on the up-conversion emission performance of Mn<Superscript>2+</Superscript>, Yb<Superscript>3+</Superscript>, Er<Superscript>3+</Superscript>: ZnWO<Subscript>4</Subscript> green phosphors

The Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors are synthesized successfully through the high temperature solid state reaction method. The micro-structure and morphology have been investigated by means of XRD and EDS. The doped concentrations of Mn²⁺, Yb³⁺, Er³⁺ are measured by ICP. The absorption spectra and emission spectra with different doped concentrations of Mn²⁺ are presented to reveal the influence of Mn²⁺ on the green up-conversion performance. Excited with 970 nm LED, the up-conversion emission peak at 547 nm is obtained and the CIE spectra as well as the green light photo are also presented. The results indicate that the Mn²⁺ ions play the role of the luminescence adjustment in the up-conversion process, which can improve the up-conversion green emission intensity effectively. The luminescence adjustment mechanism of Mn²⁺ ions in Mn²⁺, Yb³⁺, Er³⁺: ZnWO₄ green phosphors has been discussed. The crystal parameters of Dq, B and C are calculated to evaluate the energy level split effect.     

Up-conversion luminescence properties of Y2O2S:Yb,Er nanophosphors

Up-converting yttrium oxysulfide nanomaterials doped with ytterbium and erbium (Y₂O₂S:Yb³⁺,Er³⁺) were prepared with the flux method. The precursor oxide materials were prepared using the combustion synthesis. The morphology of the oxysulfides was characterized with transmission electron microscopy (TEM). The particle size distribution was 10–110 nm, depending on the heating temperature. According to the X-ray powder diffraction (XPD), the crystal structure was found hexagonal and the particle sizes estimated with the Scherrer equation agreeded with the TEM images. Upon the 970 nm infrared (IR) laser excitation, the materials yield moderate green ((²H_11/2, ⁴S_3/2) → ⁴I_15/2 transition) and strong red (⁴F_9/2 → ⁴I_15/2) luminescence. The green luminescence was enhanced with respect to the red one by an increase in both the crystallite size and erbium concentration due to the cross-relaxation (CR) processes. The most intense up-conversion luminescence was achieved with x_Yb and x_Er equal to 0.10 and 0.005, respectively. Above these concentrations, concentration quenching occurred.     

Up-conversion luminescence properties of Y2O2S:Yb3+,Er3+ nanophosphors

Up-converting yttrium oxysulfide nanomaterials doped with ytterbium and erbium (Y₂O₂S:Yb³⁺,Er³⁺) were prepared with the flux method. The precursor oxide materials were prepared using the combustion synthesis. The morphology of the oxysulfides was characterized with transmission electron microscopy (TEM). The particle size distribution was 10–110 nm, depending on the heating temperature. According to the X-ray powder diffraction (XPD), the crystal structure was found hexagonal and the particle sizes estimated with the Scherrer equation agreeded with the TEM images. Upon the 970 nm infrared (IR) laser excitation, the materials yield moderate green ((²H_11/2, ⁴S_3/2) → ⁴I_15/2 transition) and strong red (⁴F_9/2 → ⁴I_15/2) luminescence. The green luminescence was enhanced with respect to the red one by an increase in both the crystallite size and erbium concentration due to the cross-relaxation (CR) processes. The most intense up-conversion luminescence was achieved with x_Yb and x_Er equal to 0.10 and 0.005, respectively. Above these concentrations, concentration quenching occurred.     

The effect of pumping power on fluorescence behavior of LiNdP4O12 nanocrystals

The impact of excitation intensity on the Stokes and anti-Stokes luminescent properties of Nd³⁺ ions in stoichiometric LiNdP₄O₁₂ nanocrystalline powders was investigated. The Stokes fluorescence of the spectra relative intensities were strongly affected by excitation power at double 808 and 830 nm. The fluorescence decay became nonexponential and shortened with the pumping power increase. The efficient up-conversion under strong 808 nm excitation was observed in the visible range and four anti-Stokes bands were assigned. The up-conversion intensity was raising with a remarkably long time constant equal to around 1 s, which decreased with the pumping power increase.     

Spontaneous emission into planar multi-dielectric microcavities: Theoretical and experimental analysis of rare earth ion radiations

Spontaneous emission control for rare earth ions implanted inside planar multidielectric microcavities is investigated theoretically and experimentally. Rigorous classical electrodynamics analyses are presented and compared in order to compute the electromagnetic power provided by sources located inside planar dielectric multilayer structures. Radiation patterns and lifetime measurements are performed in Ta₂O₅/SiO₂ microcavities implanted with erbium and praseodymium ions. Although we demonstrate a significant enhancement of the spontaneous emission in a direction normal to the layer (up to 30%), we show that a large amount of the emitted power is carried by the guided modes of the structures.     

Up-conversion processes in NaLaF4:Er

Structural and spectroscopic investigation of NaLaF₄:Er³⁺ material at different doping concentrations is presented. X-ray diffraction patterns, up-conversion luminescence spectra and decay curves for ²H_9/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 optical transitions in the material are shown and possible excitation routes are discussed. Raman spectrum for the undoped material is presented and the effective phonon energy of the material is estimated. Based on the obtained results application of rare-earth doped NaLaF₄ in the field of up-conversion phosphors is evaluated.     

Hydrothermal synthesis and infrared to visible up-conversion luminescence of Ho3+/Yb3+ co-doped Bi2WO6 nanoparticles

In this paper, Ho³⁺/Yb³⁺ co-doped Bi₂WO₆ (Ho³⁺/Yb³⁺-Bi₂WO₆) nanoparticles were successfully synthesized by a facile hydrothermal method followed by a heat treatment process. X-ray diffraction, field emission-scanning electron microscopy, energy dispersive spectroscopy and up-conversion luminescence spectra were used to characterize the as-synthesized Ho³⁺/Yb³⁺-Bi₂WO₆. The effects of Yb³⁺ concentration on up-conversion luminescence properties were investigated. Under 980?nm laser excitation, two emission peaks centered at 546?nm and 655?nm corresponding to the ⁵F₄, ⁵S₂ and ⁵F₅ transitions, respectively, to the ⁵I₈ ground state were observed. Power studies revealed that a two-photon process was involved in the up-conversion emissions and the probable up-conversion emission mechanisms were discussed according to the energy transfer process. This study confirms that Bi₂WO₆ could be a potential host to achieve desired up-conversion luminescence and might be potentially applied in the fields of photocatalysis and solar cells.     

Effects of the annealing temperature on the structure and up-conversion photoluminescence of ZnO film

The up-conversion film is being tried to increase the photoelectric conversion efficiency of the silicon solar cell. To improve the efficiency of the photoluminescence film, the effects of the annealing temperature were investigated on the structure and photoluminescence of the ZnO up-conversion film, which was prepared using the sol-gel method and the spin-coating technique. The results show that the organic compounds and water in the ZnO film were completely eliminated when the annealing temperature reached 500?°C. The crystallinity of film is improved and the average grain size continuously increases as increasing the annealing temperature. The transmittance in the wavelength range of 400–2000?nm continuously increases as the annealing temperature increases from 500?°C to 700?°C, whilst it decreases first and then increases as the annealing temperature increases from 800?°C to 1000?°C. When the film is excited with a laser of 980?nm, there are two intense emission bands in the up-conversion emission spectra, 542-nm green light and 660-nm red light, corresponding to Ho³⁺: ⁵S₂/⁵F₄?→?⁵I₈?and ⁵F₅?→?⁵I₈ transitions, respectively. In addition, the intensity of up-conversion luminescence for the film increases first and then decreases with the increase of the annealing temperature. When the annealing temperature is at 900?°C, the film consists of small round compact particles with a high degree of crystallization, reaching maximum up-conversion intensity of the film.     

Effect of erbium on varistor characteristics of vanadium oxide-doped zinc oxide ceramics

The effect of erbium addition on microstructure, electrical properties, and ageing behavior of vanadium oxide-doped zinc oxide varistor ceramics was systematically investigated. Analysis of the microstructure indicated that the ceramics added with erbium consisted of ZnO grain as a main phase and secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, ErVO₄, V₂O₅, and Mn-rich. The average grain size decreased from 5.5 to 5.2 μm up to 0.05 mol%, whereas a further addition gradually increased it to 5.7 μm at 0.25 mol%. The sintered density increased from 5.51 to 5.61 g/cm³ with an increase in the amount of Er₂O₃. With increasing the amount of Er₂O₃, the breakdown field increased from 4,800 to 5,444 V/cm up to 0.05 mol%, whereas a further addition decreased it to 4,061 V/cm at 0.25 mol%. The varistor ceramics added with 0.05 mol% Er₂O₃ additives induced excellent nonlinear properties, with nonlinear coefficient of 63.4 by properly adding the amount of Er₂O₃ (0.05 mol%). The study indicated that the erbium acted as a donor to increase the donor concentration with an increase in the amount of Er₂O₃.     

The effect of SiO2 on TiO2 up-conversion photoluminescence film

In order to increase the photoelectric conversion efficiency of silicon solar cell, the up-conversion film has been tried to enhance the response of the solar cells to the infrared band. Yb³⁺, Er³⁺ co-doped SiO₂/TiO₂ composite films with different Ti/Si molar ratio were deposited on the glass substrate with sol–gel method and spin-coating technique. The effect of different molar ratio of Ti/Si on the film’s morphology and optical properties was investigated. The morphology, the absorption spectra and photoluminescence (PL) spectra of the film were tested and analyzed. After the film was annealed at 900 °C, the XRD diffraction pattern indicated that rare earths ions have evenly dispersed into the matrix lattice. The FT-IR showed that Si ions entered into the lattice of titanium dioxide, and the Ti–O–Si bonds came into being. When the film pumped with a laser of 980 nm, there were a dominant red emission and several weak green peaks. In addition, with the increase of the mole ratio of Si/Ti, the intensity of the film’s up-conversion luminescence increases at first and then decreases. When the molar ratio of Si/Ti is 1/8, the sample had the highest intensity of up-conversion luminescence.     

Electrospun Er:TiO2 nanofibrous films as efficient photocatalysts under solar simulated light

TiO₂ nanofibrous films with variable amounts of erbium were prepared via electrospinning. Analytical results demonstrated that the doping of erbium inhibited the phase transformation and the crystallite growth of TiO₂. The doped samples were more efficient for degradation of methylene blue than TiO₂, and an optimal dosage of erbium at 0.5% activated at 773 K achieved the highest degradation rate. The higher photoactivity might be attributable to the transition of 4f electrons of erbium, particle size, phase composition and the increase of the separating rate of photogenerated charges by erbium doping.     

Fiber ring laser with locked relaxation oscillations

An investigation is made of the locking of the relaxation oscillations in a fiber ring laser with an active medium of phosphorus aluminosilicate glass doped with erbium and ytterbium ions. It is shown that stable pulse-periodic emission in the 1.5 /gmm range can be achieved at a pulse repetition frequency between 80 and 160 kHz with a pulse length of 2–3 μs. A single-mode model is used to determine the laser parameters (the pumping rate and the photon lifetime in the cavity). Pis’ma Zh. Tekh. Fiz. 25, 24–28 (January 26, 1999)     

Up-conversion emission in KGd(WO4)2 single crystals triply-doped with Er/Yb/Tm, Tb/Yb/Tm and Pr/Yb/Tm ions

Triply-doped single crystals KGd(WO₄)₂:Er³⁺/Yb³⁺/Tm³⁺, KGd(WO₄)₂:Tb³⁺/Yb³⁺/Tm³⁺ and KGd(WO₄)₂:Pr³⁺/Yb³⁺/Tm³⁺ were grown by the Top Seeded Solution Growth (TSSG) method, with an aim of getting efficient up-converted multicolored luminescence, which subsequently can be used for generation of white light. Such an aim determined the choice of the triply doped compounds: excitation of the Yb³⁺ ions in the infrared spectral region is followed by red, green and blue emission from other dopants. It was shown that all these systems exhibit multicolor up-conversion fluorescence under 980 nm laser irradiation. Detailed spectroscopic studies of their absorption and luminescence spectra were performed. From the analysis of the dependence of the intensity of fluorescence on the excitation power the conclusion was made about significant role played by the host’s conduction band and other possible defects of the KGd(WO₄)₂ crystal lattice in the up-conversion processes.     

Infrared-to-visible conversion luminescence of Er3+ ions in lead borate transparent glass-ceramics

Transparent glass-ceramics were successfully prepared during controlled heat treatment of lead borate glasses. The PbF₂ particles were dispersed into a borate glass matrix which was evidenced by X-ray diffraction analysis. The phase identification revealed that crystalline peaks can be related to the orthorhombic PbF₂ phase. Green up-conversion luminescence due to the ⁴S_3/2–⁴I_15/2 transition of Er³⁺ ions was registered. In comparison to the precursor glass the luminescence intensity was considerably higher, whereas the luminescence linewidth slightly decreased in the studied oxyfluoride transparent glass-ceramics. It indicated that a part of the trivalent erbium was incorporated into the PbF₂ crystalline phase.     

Growth of praseodymium tartrate crystals in silica gel

The growth of praseodymium tartrate crystals in the system Pr(NO₃)₃-Na₂ SiO₃-C₄H₆O₆, using a single-tube-single-gel technique is described. The growth conditions are delineated and a spherulitic morphology is reported. The spikes attached to the spherulites are single crystals of praseodymium tartrate. The mechanisms of crystallization for various types of spherulites are described. The information presented contributes to the understanding of spherulitic growth in general, and that of praseodymium tartrate in particular.