M. Jiménez de Castro

Nanostructuring the Er–Yb distribution to improve the photoluminescence response of thin films

Thin films of amorphous aluminum oxide (a-Al2O3) codoped with Er3+ and Yb3+ ions have been in-depth nanostructured by distributing the rate earth (RE) ions in layers separated in the 0–3 nm range. The Yb to Er concentration ratio is varied from 0 to 3.6. The photoluminescence (PL) response at 1.53 μm exhibits an increase of up to two orders of magnitude with respect to that of films doped only with Er. The PL intensity is improved when Yb3+ and Er3+ ions are in separate layers and the results show that efficient Yb3+ to Er3+ energy transfer can be achieved for separations up to 3 nm. Furthermore, it is shown that designing an adequate RE distribution, for the same total RE content and Yb to Er concentration ratio, can enhance the PL intensity by a further factor of two. It is shown that the Er3+ PL response is improved because of a reduction of the RE clustering and an improvement of the energy transfer from Yb3+ to Er3+ ions.

Photoluminescence performance of pulsed-laser deposited Al2O3 thin films with large erbium concentrations

Erbium doped Al2O3 films with concentrations up to 6×1020 Er cm−3 have been prepared in a single step process by pulsed-laser deposition. Alternate ablation of Al2O3 and Er targets has been used to control the in-depth distribution and in-plane concentration of Er3+ ions independently. The characteristic Er3+ photoluminescence response at 1.53 μm has been studied as a function of the Er3+ distribution. It is found that lifetime values can be greatly increased by increasing the Er3+–Er3+ in-depth separation above 3 nm. This result can be related to a reduced Er3+–Er3+ energy migration process. The in-plane Er3+ concentration was increased by either increasing the number of pulses on the Er target or the laser energy density for ablation. By the latter method in-plane concentrations as high as 1.1×1014 Er cm−2 per layer (corresponding to 2×1020 Er cm−3) were achieved, while keeping lifetime values as high as 6 ms. This result is explained in terms of shallow Er3+ implantation during deposition.

The role of Er3+–Er3+ separation on the luminescence of Er–doped Al2O3 films prepared by pulsed laser deposition

Erbium-doped Al2O3 films have been deposited in a single step process by pulsed laser deposition using independent ablation of Al2O3 and Er targets. This procedure allows to control the Er3+ ions in-depth distribution. The characteristic Er3+ photoluminescence at 1.54 μm shows lifetime values which increase from 6.0 to 7.1 ms when the Er3+–Er3+ in-depth separation is increased from 3 to 9 nm. These results are discussed in terms of the ion–ion interaction and clustering for separations shorter than 6 nm.

Melting and solidification of Bi nanoparticles in a germanate glass

A very large melting?solidification hysteresis of Bi nanoparticles embedded in a bulk alkali germanate glass is reported. Heating and cooling cycles are reproducible and show reversible transitions. High resolution transmission electron microscopy reveals that the glass contains nanocrystals of elementary Bi which are a few tenths of a nanometre in size. Upon heating above the Bi melting temperature the glass transmission increases up to 10% with respect to the initial value, which is most likely related to Bi melting. Upon cooling this high transmission state remains up to temperatures as low as 436?K. This behaviour is confirmed by Raman spectroscopy measurements. This nanostructured glass with a high refractive index can be used in nonlinear optical applications as well as an optical thermo-sensor.

Optically active Er–Yb doped glass films prepared by pulsed laser deposition

Active rare-earth Er3+–Yb3+ co-doped phosphate glass films are produced in a single step by pulsed laser deposition. The films are multimode waveguides and exhibit the highest refractive index, optical density and 1.54 μm photoluminescence intensity and lifetime when deposited at low oxygen pressure (Pox⩽4×10−5 Torr). The density of the films obtained under these conditions is higher than that of the target material as a consequence of the high kinetic energy of the species generated during ablation. Luminescent emission can be excited by optical pumping the Er3+ ions either directly or through cross-relaxation of the Yb3+. Post-deposition annealing allows us to improve the luminescence performance.

Potential of bismuth nanoparticles embedded in a glass matrix for spectral-selective thermo-optical devices

The optical transmission at a fixed visible wavelength of Bi nanoparticles embedded in a dielectric is known to show a sharp hysteretic evolution as a function of the temperature due to the reversible melting-solidification of the nanoparticles. In this work, we explore the temperature-dependent optical response of Bi nanoparticles embedded in a doped germanate glass (GeO2-Al2O3-Na2O) in a broad range from the visible to the near infrared. The transmission contrast induced by melting of the nanoparticles is shown to be strongly wavelength-dependent and evolves from positive to negative as the wavelength increases. This behaviour is well modelled using effective medium calculations, assuming that the nanoparticles size, shape, and distribution are unmodified upon melting, while their dielectric function turns from that of solid Bi to that of liquid Bi thus modifying markedly their optical response. These results open a route to the spectral tailoring of the thermo-optical response of Bi nanoparticles-based...

Exciton-erbium coupling in SiOx suboxide films prepared by combining sol-gel chemistry and ion implantation

The efficiencies of three methods based on a combination of sol � /gel chemistry and ion implantation for obtaining an optical activation of Er atoms via the transfer of excitons energy are compared. A better coupling is observed in silica-gel containing Er prepared by addition of Er nitrate to the tetraethoxysilane sol and embedding Si nanocrystals formed by ion implantation or in a silicon suboxide derived from triethoxysilane and implanted with Er ions than in silica-gel implanted sequentially with Si then Er. The infrared emission of Er ions is reduced by the segregation of erbium oxide or the precipitation of Er5Si3, depending on the matrix, in films containing more than 1 at.% Er annealed at temperatures over 1000 8C. # 2002 Elsevier Science B.V. All rights reserved.

Infrared luminescence of erbium-doped sodium lead germanate glass

The infrared optical properties of Er3+ ions are reported for 60GeO2–20PbO–20Na2O glass for two Er2O3 concentrations. From the optical absorption spectra, the Judd–Ofelt (J–O) parameters have been obtained and have been used to calculate radiative lifetimes and stimulated emission cross sections. A narrow emission band peaked at 1536 nm with exponential decay for both Er concentrations is observed. The measured lifetime decreases for increasing Er concentration, its value being very close, in the case of the lowest doping level, to the radiative lifetime calculated from J–O analysis. This, together with the relatively high emission cross section makes this glass suitable for laser applications.

a-Si nanolayer induced enhancement of the 1.53μm photoluminescence in Er3+ doped a-Al2O3 thin films

A structured film formed by an active Er3+-doped amorphous Al2O3 layer located between two amorphous silicon nanolayers (NLs) in as-grown conditions shows an enhancement of the photoluminescence (PL) intensity and lifetime at 1.53μm of one order of magnitude when compared to a similar Er3+-doped film without silicon NLs. The film can be pumped even under nonresonant excitation conditions as a result of a long range energy transfer from the a-Si NLs to the Er3+ ions. In addition, the PL shows a single exponential decay with a lifetime value as high as 2.4ms. The lifetime enhancement is associated with an improvement of the emission efficiency of the Er3+ ions.

Erbium Luminescence in Suboxide Films Derived from Triethoxysilane

Silicon nanoclusters formed in triethoxysilane during annealing at temperatures above 900°C are used for increasing the excitation cross section of Er atoms. A stronger sensitization of the Er luminescence is observed, for a given Er concentration, when the Er3+ ions are introduced in the matrix by ion implantation than when adding a salt to the precursor solution, because of a better dispersion of the implanted atoms. The logarithmic increase of the emission yield with the Er concentration up to 1 at% which is found in the case of implanted samples is ascribed to the quenching processes by interaction between neighbour Er3+ ions.