Visible Luminescence Properties Research Articles

Infrared to visible upconversion luminescence properties in the system Ln 2BaZnO 5 (Ln = La, Gd)

We have investigated the upconversion properties of the rare-earth doped systems La 2BaZnO 5 ( I4/ mcm) and Gd 2BaZnO 5 ( Pbnm). The dependence of the luminescence properties on the identity and the concentration of the dopants, Er 3+ and Er 3+ co-doped with Yb 3+, as well as on the synthetic route, was examined. Following coherent excitation at 975 nm, strong upconversion emission was observed in the visible region (525, 550 and 660 nm). Power dependence studies revealed a two photon process for these emissions. In the co-doped samples, a blue emission (410 nm) could also be observed. For this emission, the power dependence studies confirmed a three photon process.

Spectroscopic investigations of Nd3+-, Er3+-, Er3+/Yb3+-, and Tm3+-ions doped SiO2–Al2O3–CaF2–GdF3 glasses

Abstract This paper reports on the absorption, visible and near-infrared luminescence properties of Nd3+, Er3+, Er3+/2Yb3+, and Tm3+ doped oxyfluoride aluminosilicate glasses. From the measured absorption spectra, Judd–Ofelt (J–O) intensity parameters (Ω2, Ω4 and Ω6) have been calculated for all the studied ions. Decay lifetime curves were measured for the visible emissions of Er3+ (558 nm, green), and Tm3+ (650 and 795 nm), respectively. The near infrared emission spectrum of Nd3+ doped glass has shown full width at half maximum (FWHM) around 45 nm (for the 4F3/2→4I9/2 transition), 45 nm (for the 4F3/2→4I11/2 transition), and 60 nm (for the 4F3/2→4I13/2 transition), respectively, with 800 nm laser diode (LD) excitation. For Er3+, and Er3+/2Yb3+ co-doped glasses, the characteristic near infrared emission bands were spectrally centered at 1532 and 1544 nm, respectively, with 980 nm laser diode excitation, exhibiting full width at half maximum around 50 and 90 nm for the erbium 4I13/2→4I15/2 transition. The measured maximum decay times of 4I13/2→4I15/2 transition (at wavelength 1532 and 1544 nm) are about 5.280 and 5.719 ms for 1Er3+ and 1Er3+/2Yb3+ (mol%) co-doped glasses, respectively. The maximum stimulated emission cross sections for 4I13/2→4I15/2 transition of Er3+ and Er3+/Yb3+ are 10.81×10−21 and 5.723×10–21 cm2. These glasses with better thermal stability, bright visible emissions and broad near-infrared emissions should have potential applications in broadly tunable laser sources, interesting optical luminescent materials and broadband optical amplification at low-loss telecommunication windows.

Optical characteristics of Si/SiO 2 multilayers prepared by magnetron sputtering

Si/SiO 2 multilayers have been successfully prepared by magnetron sputtering and subsequently thermal annealed in an Ar atmosphere at a temperature of more than 500 °C. The surface of the as-deposited films is compact and smooth, and the distribution of grain size estimated to be 20 nm is uniform. For Si/SiO 2 multilayers annealed at 1100 °C, the Si sublayer sandwiched between potential barrier SiO 2 is crystalline structure by means of the analysis of Raman spectra and XRD data. The visible PL peak accompanying to a blue-shift with the decrease of Si sublayer thickness has been observed, and the intensity of this peak enhances with the increase of annealing temperature. The visible luminescence properties of Si/SiO 2 multilayers can be ascribed to quantum confinement of electron–hole pairs in quantum wells with grain size lower than 4.5 nm. In Si/SiO 2 multilayers, not only quantum confinement but also Si–SiO 2 interface states play an important role in the optical transition. The PL peak located at 779 nm is independent of the thickness of Si sublayer, so it may be ascribed to interface mediated transition. Typical Si dangling bonds defect could be a dominating obstacle to high luminescence efficiencies.

Spectral analysis of RE3+ (RE = Er, Nd, Prand Ho):GeO2–B2O3–ZnO–LiF glasses

This paper reports on the absorption, visible and near-infrared luminescence properties ofEr3+,Nd3+,Pr3+ and Ho3+-doped alkali fluoride zinc boro germanate glasses. The x-ray diffraction(XRD) and differential thermal analysis (DTA) profiles of the host glasshave been carried out, to confirm its structure and thermal stability. Fromthe measured absorption spectra, Judd–Ofelt (JO) intensity parameters(Ω2,Ω4 and Ω6) have been calculated for all the studied ions. ForPr3+ and Ho3+-doped glasses, upconversion emission spectra have also beenmeasured. Decay curves were measured for the visible emissions ofEr3+,Pr3+ andHo3+ ions at 547 nm(Er3+: green), 604 nm and641 nm (Pr3+: orange andred) and 658 nm (Ho3+: red), respectively. The near-infrared emission spectra ofEr3+/Yb3+ and Nd3+-doped glasses have shown full width at half maximum (FWHM) around 95 nm (for the transition) and 63 nm (for the transition), respectively. The measured maximum decay times of transition (at wavelength 1.51 µm) are about 5.72 ms and 6.14 ms for1.0Er3+ and 1.0Er3+/ 2Yb3+ (mol%)-codoped glasses, respectively. The maximum stimulated emission crosssections for transition of Er3+ and Er3+/Yb3+ are 5.447 × 10−21 cm2 and 4.540 × 10−21 cm2. These glasses with better thermal stability, bright visible emissions and broadnear-infrared emissions should have potential applications in broadly tunable laser sources,interesting optical luminescent materials and broadband optical amplification in low-losstelecommunication windows.

Preparation and characterization of UV‐curable ZnO/polymer nanocomposite films

AbstractA series of novel nano‐ZnO/polymer composite films with different ZnO contents was prepared through incorporation of pre‐made colloidal ZnO particles into monomer mixtures of urethane‐methacrylate oligomer and 2‐hydroxyethyl methacrylate, followed by ultraviolet (UV) radiation‐initiated polymerization. The colloidal ZnO nanoparticles with a diameter of 3–5 nm were synthesized from zinc acetate and lithium hydroxide in ethanol via a wet chemical method. In order to stabilize and immobilize the ZnO particles into the polymer matrix, the ZnO nanoparticles were further capped using 3‐(trimethoxysilyl)propyl methacrylate. Thermogravimetric analyses show that the ZnO nanoparticles were successfully incorporated into the polymer matrix and these ZnO/polymer composites have a good thermal stability. Transmission electron microscopy studies indicate the ZnO nanoparticles were uniformly dispersed in the polymer and they remained at the original size (3–5 nm) before immobilization. All nanocomposite films with ZnO particle contents from 1 to 15 wt% show good transparency in the visible region and luminescent properties. In addition, composite films with high ZnO content (>7 wt%) are able to absorb UV irradiation below 350 nm, indicating that these composite films exhibit good UV screening effects. Copyright © 2006 Society of Chemical Industry

The luminescence of CaYBO4:RE3+ (REEu, Gd, Tb, Ce) in VUV–visible region

Phosphors CaYBO4:RE3+ (RE = Eu, Gd, Tb, Ce) were synthesized with the method of solid-state reaction at high temperature, and their vacuum ultraviolet (VUV)-visible luminescent properties in VUV-visible region were studied at 20 K. In CaYBO4, it is confirmed that there are two types of lattice sites that can be substituted by rare-earth ions. The host excitation and emission peaks of undoped CaYBO4 are very weak, which locate at about 175 and 350-360nm, respectively. The existence of Gd3+ can efficiently enhance the utilization of host absorption energy and result in a strong emission line at 314 nm. In CaYBO4, Eu3+ has typical red emission with the strongest peak at 610 nm; Tb3+ shows characteristic green emission, of which the maximum emission peak is located at 542 nm. The charge transfer band of CaYBO4:Eu3+ was observed at 228 nm; the co-doping of Gd3+ and Eu3+ can obviously sensitize the red emission of Eu3+. The fluorescent spectra of CaYBO4:Ce3+ is very weak due to photoionization; the co-addition of Ce3+-Tb3+ can obviously quench the luminescence of Tb3+. (C) 2006 Elsevier B.V. All rights reserved.

Visible cathodoluminescence from mechanically milled germanium

There has been interest in the past years in the visible luminescence properties of germanium nanocrystals. Most of the previous works refer to Ge nanocrystals embedded in an oxide matrix. In this work nanocrystalline germanium has been prepared by high-energy ball milling of Ge single crystals and Ge powder. The structure of the milled samples has been assessed by x-ray diffraction (XRD) and transmission electron microscopy (TEM) while the luminescence has been investigated by cathodoluminescence (CL) in the scanning electron microscope (SEM). The samples consist of a powder of particles with sizes of hundreds of nanometres, normally aggregated to form larger particles. TEM reveals that the particles consist of nanocrystals with a wide range of sizes including crystallites of some nanometres. Milled Ge shows two CL bands at about 2.4–2.5 eV and 3.1 eV, respectively. Both emissions appear to be related to the presence of Ge nanocrystals. The CL of untreated and milled GeO2 powder has been also investigated for comparison.

Infrared and visible luminescence properties of Er3+ and Yb3+ ions codoped Ca3Al2Ge3O12 glass under 978 nm diode laser excitation

Er 3+ and Yb3+ ions codoped calcium aluminum germanate glass has been synthesized by solid-state reaction. An intense infrared emission at 1534 nm, which corresponds to the minimum losses of silica based fibers used in optical communications, and visible emissions at 416, 490, 525, 548, and 660 nm, corresponding to the I13/24→I15/24, H9/22→I15/24, F7/24→I15/24, H11/22→I15/24, S3/24→I15/24, and F9/24→I15/24 transitions of Er3+ ions, respectively, were simultaneously observed in this glass under the excitation of a 978 nm diode laser at room temperature. These emissions are mainly attributed to energy transfer from Yb3+ ions to Er3+ ions. The up-conversion processes involve a sequential two-photon absorption for the red (660 nm), the green emissions (525 and 548 nm) and the blue emission (490 nm), and a sequential three-photon absorption for the violet-bluish emission (416 nm). The up-conversion fluorescence of Ca3Al2Ge3O12:Er,Yb glass can be used to detect 980 nm infrared laser light.

Visible Luminescence and Surface Properties of Nanosized ZnO Colloids Prepared by Hydrolyzing Zinc Acetate

Luminescence properties of nanosized zinc oxide (ZnO) colloids greatly depend on their surface properties. These surface properties in turn are largely determined by the method of preparation. The procedure for producing ZnO colloids consists of two major steps: (1) preparing the precursor by reacting zinc acetate with ethanol and (2) hydrolyzing the precursor to form the colloid by using lithium hydroxide. The sample colloids in this study were prepared by hydrolyzing zinc acetate precursors containing various concentrations of Zn2+ with different concentrations of lithium hydroxide. The luminescence properties were evaluated by the energy difference, ΔE, between the band gap and the emission energy which were obtained from the onset of the absorption spectrum and the peak wavelength of the emission spectrum, respectively. The surface properties of ZnO particles were studied using thermal gravimetric and infrared techniques. ZnO particles produced via these procedures are not pure but have acetate (CH3C...

Optical spectra of silicon nanostructures from the random-matrix model

We apply the method of random matrices to a calculation of the optical properties of porous silicon and silicon nanopowders, analyzing the effects of disorder on the visible luminescence properties. The maximum of the luminescence peal; displays a blueshift, which adds up to the effects induced by other mechanisms, such as quantum confinement or surface passivation, and agrees with the experimental findings, The long-wavelength luminescence edge, instead, is redshifted by the presence of disorder, thus partially compensating for the gap-opening effect induced by the other mechanisms.

Silicon Cluster Terminated by Hydrogen, Fluorine and Oxygen Atoms: A Correlation with Visible Luminescence of Porous Silicon

The effect of hydrogen, fluorine and oxygen surface termination atoms together with size dependence of the Si-cluster on the electronic structure are considered, using semiempirical molecular orbital calculations. The results show that the electronic structure of the Si-cluster is strongly affected by the presence of oxygen terminators which enhance the carrier localization. The transition probability between the electronic states support the high efficiency of visible luminescence. The hydrogen termination leads to a stable Si-cluster structure. Our calculations suggest that surface conditions of the Si-cluster and its size, are responsible for the visible luminescence properties of porous Si. The oxygen surface termination of the Si-ciuster is one of the requisite conditions to obtain luminescence in the red-orange region.