Patrick Aschehoug

Luminescence properties of YVO4:Ln (Ln = Nd, Yb, and Yb-Er) nanoparticles

Concentrated colloidal solutions of well dispersed YVO4:Ln (Ln ¼ Nd, Yb, and Yb–Er) nanocrystals are synthesized through the precipitation of citrate complexes of rare earth salts with sodium orthovanadate. Luminescence spectra of aqueous suspensions of YVO4:Nd or Yb are very similar to the bulk material, with lower lifetimes of the emitting level. After heating at 600 C, the luminescence properties of silica capped YVO4:Ln nanoparticles are significantly improved. In these conditions, YVO4:Yb, Er nanoparticles exhibit green up-conversion luminescence and 1.55 lm emission of the erbium ion under infrared excitation of the ytterbium ion. 2003 Elsevier Science B.V. All rights reserved.

Optical properties of neodymium and dysprosium doped hybrid siloxane–oxide coatings

Hybrid organic–inorganic nanocomposites made of metal oxo-polymers (zirconium and neodymium oxo or dysprosium oxo species) linked to siloxane species [(CH3)Si–Oz.frac32;] exhibit luminescence. At low rare-earth-metal (M = Dy, Nd) concentrations, the emission lifetime is mainly governed by energy-transfer processes between rare-earth-metal cations. At higher rare-earth-metal concentrations the emission lifetime is controlled by the interactions between rare-earthmetal cations and by an increase of the quenching probability due to the vicinity of some residual hydroxy groups. Energy transfer between Nd3+ ions and Rhodamine 6G co-incorporated inside these hybrid coatings is also demonstrated.

Growth by laser ablation of Y2O3 and Tm∶Y2O3 thin films for optical applications

Crystalline undoped and thulium doped yttrium oxide (Y2O3) thin films have been grown by the pulsed laser deposition (PLD) technique on various single-crystal substrates heated at 700 °C. X-Ray diffraction (XRD) analysis showed that the orientations of the films depended on the substrate and on the oxygen pressure. The crystalline quality of Y2O3 thin films, studied by rocking-curve measurements and by Rutherford backscattering spectroscopy (RBS) in channeling geometry, and the in-plane orientations between films and substrates, determined by X-ray asymmetric diffraction, were also found to depend on the same parameters. The recording of the visible fluorescence spectra of the thulium (Tm) doped Y2O3 thin films, as well as the measurements of the fluorescence lifetimes of the 1D2 and 1G4 thulium emitting levels, gave results very similar to those obtained on bulk crystals. Doping rates in Tm of 0.5 and 1% were found to limit Tm–Tm interactions inside the films and to give relatively high visible fluorescence intensities.

Rare earth doped mesoporous hybrid thin films with tunable optical responses

Optical quality mesostructured silica thin films functionalized with three large hydrophobic organosilylated quinizarin derivatives are prepared via evaporation induced self-assembly (EISA). Incorporation of Eu3+ is performed by post-reacting the functionalized layers with several europium precursors. Unambiguous location of the quinizarin moieties inside the porosity and their accessibility to Eu3+ ions are demonstrated using XRD, SAXS and fluorescence measurements. Complexation of Eu3+ reduces the fluorescence of quinizarin; for some europium precursors an energy transfer between the grafted organic dye and the lanthanide is clearly observed. The luminescence intensity of Eu3+ can be tuned by varying the nature of the rare earth precursor, the mesophase and the chelate itself. The resulting optical responses differ with respect to concentration, lifetime and local environment of Eu3+ inside the thin films. Additionally, efficient energy transfer from Tb3+ to Eu3+ and electronic coupling probed by EPR between Cu2+ cations trapped in such mesoporous hybrid films give strong evidence of the presence of several metal ions per pore.

Eu3+-doped CdS nanocrystals in SiO2 matrices : one-pot sol-gel synthesis and optical characterization

An enhancement of the europium luminescence has been reported in Eu-doped SiO2 materials by interaction with adsorbed CdS nanoparticles. In this paper, the preparation of homogeneous Eu3+-doped CdS nanocrystals embedded in SiO2 sol–gel matrices by a simple “one-pot” method is reported. The synthesis conditions have been varied in order to modify the distribution of the lanthanide ions and the CdS nanoparticles within the nanocomposite. The structural modifications involve different strengths in the Eu3+–CdS interaction. The effect of these interactions on the Eu3+ luminescence is discussed. The absorption, excitation and emission spectra of the Eu3+ species, as well as the time-resolved luminescence, revealed the existence of an efficient CdS → Eu3+ energy transfer, responsible for the increase in the fluorescence intensity. However, when these species are spatially close, a diminution of the total emission and lifetime values is observed as a result of a back transfer from the Eu3+ ions to CdS nanoparticles.

Nd :GdCOB: overview of its infrared, green and blue laser performances

Abstract GdCOB (Ca4GdB3O10) is a new non-linear optical material which can be grown in large sized crystals by the Czochralski method. In this material, part of the gadolinium ions can be replace by Nd3+ without significant decrease of the crystal quality. Nd:GdCOB single crystals exhibit laser action in the infrared at 1060 and 1091 nm simultaneously. The two transitions involved originating from the two Kramers doublets of the 4F3/2 state, their respective contributions depend upon the temperature of the Nd:GdCOB crystal. By combining the non-linear properties of the GdCOB matrix and the laser emission due to ND3+ ions, it is possible to generate directly by self-frequency doubling 115 mW of green laser light at 530.5 nm under diode pumping at 810 nm. It is also possible to self-double the 936 nm emission of Nd:GdCOB, leading to blue laser emission, but only under pulsed titanium-sapphire laser pumping. However, a CW blue laser beam is obtained in Nd:GdCOB by self sum-frequency mixing of the 1090 nm laser emission and the residual pump beam at ∼812 nm, yielding 1.2 mW of 465 nm laser light, with an optical to optical efficiency of 0.3%. This paper ends with a survey of the Nd:YCOB laser characteristics which are compared to those of Nd:GdCOB.

Eu3+- and Tm3+-doped yttrium oxide thin films for optical applications

We studied here the possibility to elaborate europium-doped yttrium oxide crystallised planar wave-guide structures, and their optical properties through rare earth fluorescence emission and m-lines spectroscopy. Propagation of optical modes is compared between doped and undoped samples.

Selective excitation study of Yb3+ in GdCa4O(BO3)3 and YCa4O(BO3)3

The Yb3+-doped non-linear rare-earth calcium oxoborate crystals GdCa4O (BO3)3 (GdCOB) and YCa4O(BO3)3 (YCOB) were investigated by low-temperature absorption and selective excitation spectroscopy. The selective excitation and emission spectra revealed the spectral features of the main Yb3+ centre and the principal minority one in both crystals. The energy level schemes for these centres in both hosts, as well as structural assignments, were proposed. It was established that the minority centre, which represents about 10% of the total intensity and was assigned to Yb3+ in a Ca2+ site, is not a trap but an energy donor for the main centre. Common features of and differences between the vibronic structure of the two centres in GdCOB and YCOB are discussed. The existence of additional features in YCOB:Yb spectra is pointed out.

Spectroscopic and structural properties of Nd3+ doped strontium lanthanum aluminate laser crystals

Nd3+-activated strontium lanthanum aluminate Sr1−xNdyLax−yMgxAl12−xO19 (ASL:Nd) crystals give efficient 4F3/2→4I9/2 laser emission at 900 nm, whose properties depend on the x and y composition parameters. Based on high-resolution spectroscopy and emission decay, this paper demonstrates that the composition dependence of the laser emission is caused by the presence of two structural centers, C1 and C2, whose relative proportion in crystals is determined by composition parameter x. From the spectral data and crystal structure it is inferred that C2 center that prevails at low x, corresponds to a Nd3+ in a Sr2+ (2d) site of D3h local symmetry with no nearby Ln3+ (La3+ or Nd3+) ions. The C1 center lines, prevailing at large x parameter, which are broader and shift with composition, are composite lines of various structural centers of Nd3+ in a Sr2+ site with different occupancy of nearest-neighbor sites by Ln3+. The influence of the spectral and emission dynamics features of these centers on the laser propert...

Synthesis and luminescence properties of colloidal lanthanide doped YVO 4

Aqueous colloidal solutions of well dispersed YVO 4 :Ln (Ln = Eu, Nd) nanoparticles are synthesized through precipitation reactions at room temperature. In the case of YVO 4 :Eu, a luminescence quantum yield of 15% is found, which is not as high as in the bulk due to the existence of residual crystalline defects and nonradiative relaxations from the hydroxylated surface. Appropriate hydrothermal annealing and deuteration of the surface allow to rise the yield up to 38%. Incorporation of the nanocrystals into a transparent silica matrix is achieved through preliminary coating of the particles with a functionnalized silicon alkoxide and further dispersion into a sol-gel precursor solution. Such sol-gel materials doped with YVO 4 :Nd nanocrystals are transparent and exhibit the typical emission at 1.06 μm of the Nd 3+ ion.