J. Fick

High photoluminescence in erbium-doped chalcogenide thin films

Abstract The spectral properties of the chalcogenide glasses As2S3 and As24S38Se38-doped with Er3+ are presented and discussed. Thin films were formed by thermal evaporation and the erbium doping was obtained by subsequent ion implantation. Strong Er3+ emission at 1.54 μm has been observed. The high refractive index of these chalcogenide glasses lead to Er3+ emission cross-sections (15×10 −21 cm 2 ) which are two times higher than for doped silica glass. The lifetime of the Er3+ metastable 4I13/2 energy level was measured to be 2.3 ms. This short lifetime is consistent with the high emission cross-section. Furthermore, the very low phonon energies of chalcogenide glasses lead to relatively long lifetimes of the Er3+ 4I11/2 pump level, which have been measured to be of the order of 0.25 ms. These spectral properties make this glass a good candidate for applications in the field of integrated optics.

Microstructural and nonlinear optical properties of silica–titania sol-gel film doped with PbS quantum dots

Thin silica–titania films doped with different concentration of PbS quantum dots (PbS/oxide molar ratios ranging from 5% to 25%) were fabricated via a sol-gel route. The structural properties were studied by x-ray diffraction, high-resolution transmission electron microscopy, and Rutherford backscattering spectrometry. The PbS crystals were found to have a mean diameter in the range 2.3–3.5 nm with narrow size distribution. The resonant nonlinear optical properties were studied by the nonlinear m-line technique and degenerate four-wave mixing. High negative nonlinear refractive indices (n2) were measured at 1.064 μm. Different n2 values were obtained for nanosecond excitation (n2=10−7–10−8 cm2/kW) and for picosecond excitation (n2=10−9–10−10 cm2/kW). The differences can be explained by saturation effects. Measurements at 532 nm showed n2 values ten times higher than at 1.064 μm. The response time of the nonlinearity for both wavelengths was below 35 ps.

Active optical properties of Er-containing crystallites in sol–gel derived glass films

Abstract Thin films of controlled refractive index are prepared by sol–gel processing and thick multilayer deposits are used as planar waveguides for integrated optics (IO). By doping these layers with rare-earth ions such as Nd 3+ or Er 3+ , IO devices such as lasers or amplifiers can be fabricated; the incorporation of these active elements into crystallites offers possibilities for increased dopant concentration without quenching, improved spectroscopic performance and high gain. The controlled growth of crystallites such as Er 2 Ti 2 O 7 or ErPO 4 in SiO 2 –TiO 2 based sol–gel films through suitable heat treatments is described. The growth of crystallites was measured by grazing incidence X-ray diffraction. Doping of the glass matrix with Er-containing crystallites improved the Er fluorescence lifetime of the 1.55-μm transition, in some cases by more than 200%.

Zirconia-ormosil films doped with PbS quantum dots

Abstract Zirconia-ormosil (organically modified silicates) films doped with different concentrations of PbS quantum dots were synthesized by sol–gel processing. A sol containing 3-(trimethoxysilil)propylmethacrylate as matrix precursor was mixed with a PbS colloidal doping sol. The control of the particle size was obtained by using 3-mercaptopropyltrimethoxysilane as capping agent in the PbS colloidal sol. The microstructure of the films was investigated by Fourier transform infrared spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction and high resolution transmission electron microscopy. Linear and non-linear optical properties were studied by absorption spectrophotometery and non-linear m-line technique. A curing temperature of 130°C allowed a good degree of densification without deterioration of the sulfide particles and the change in refractive index from the substrate was sufficient to support waveguide modes. The doping concentration affected the mean particle size, shifting the linear absorption to shorter wavelengths for films doped with a smaller amount of PbS. The non-linear refractive index n 2 was measured at 1.064 μm. A negative and fully reversible non-linear effect was measured, with n 2 values in the range 10 −15 –10 −16 m 2 /W, depending on the concentration of PbS quantum dots.

Sol–gel thin film deposition and characterization of a new optically active compound: Er2Ti2O7

Abstract This paper reports on the first sol–gel thin film preparation of a new optically active compound: Er2Ti2O7 (ETO). Optical, microstructural and spectroscopic properties of ETO films annealed in a temperature range 300–1000°C are studied. This work shows that the porosity and microstructure of ETO films depend closely on the heat-treatment temperature. Photoluminescence (PL) has been observed for films heat-treated at 600°C or more. The PL decay appears strongly influenced by quenching effects. For thin films treated at 600°C, quenching is essentially due to the presence of hydroxyl groups. After heat-treatment at 800°C or more, quenching can be explained by the high concentration of erbium atoms and by their distribution in the ETO lattice.

Control of Semiconductor Particle Size in Sol-Gel Thin Films

Thin silica and silica-titania films containing CdS and PbS quantum size particles were obtained by separate preparation of the matrix and the colloidal sols and successive mixing. Sulfide particles were obtained by reaction of metal acetates with thioacetamide and control of particle size was achieved by surface capping agents. Powders and thin films deposited on soda-lime slides were prepared and characterized by XRD. Absorption spectra were recorded on films. The nonlinear refractive index was measured by anm-line technique on a CdS-doped sample. The nonlinear effect was found to be reversible and an2 value of −3 10−9 cm2/kW was measured.

Active optical properties of erbium-doped GeO2-based sol-gel planar waveguides

Abstract Er3+ doped thin glass films were produced by the sol-gel technique. The best active properties were obtained for GeO2–SiO2 matrices co-doped with P2O5 or Al2O3. We succeeded in limiting the influence of OH groups on the active properties by special heat treatments. Narrow fluorescence spectra (~20 nm) and long lifetimes (~6 ms) were found in P2O5 co-doped samples whereas Al2O3 co-doping gave wider spectra (~50 nm) with slightly lower lifetimes (~5 ms). The quenching concentration in the Al2O3 co-doped samples was 0.9% Er3+.

The effects of phosphorus on the crystallisation and photoluminescence behaviour of aerosol-gel deposited SiO2-TiO2-Er2O3-P2O5 thin films

Abstract Optically active films in the system, SiO 2 –TiO 2 –Er 2 O 3 –P 2 O 5 have been prepared by aerosol–gel deposition. Crystallisation and morphology features that determine the preparation of transparent films are described and discussed in relation to the experimental conditions. The photoluminescence (PL) behaviour is then studied and discussed in relation to the films composition and to the nature of the crystallographic phases present in the films. It is concluded that concentration quenching and co-operative up-conversion mechanisms quench noticeably the PL. A 20Ti–0.5Er–10P composition is compatible with the preparation of transparent films together with an efficient prevention of these parasitic mechanisms.

Thermally activated silver diffusion in chalcogenide thin films

Abstract Thin arsenic trisulfide films were deposited by thermal evaporation and thermally activated silver diffusion into these films was studied. UV–vis transmission and Rutherford backscattering spectrometry (RBS) was used for characterization of film property changes with Ag incorporation. The straightforward analysis proposed by Swanepoel, which allows determination of the dispersion relation and the film thickness from the optical transmission spectrum, was extended and applied to the chalcogenide thin films. RBS shows that silver diffusion mechanism depends strongly on an eventual annealing between the chalcogenide and silver deposition step. Without annealing the silver diffusion takes place by exchange between silver and arsenic atoms whereby sulfur atoms remain stationary, and arsenic accumulation occurs at the surface. For annealed samples silver diffuses without changing the film stoichiometry. In this case, the diffusion is much slower and the profile is more step-like. The possibility of using this technique for channel waveguide fabrication is demonstrated.

Aerosol–gel preparation of optically active layers in the system Er/SiO2–TiO2

Abstract Er-doped silica–titania multilayer coatings have been successfully deposited using an original sol–gel deposition technique: the Aerosol–gel process. This study is the first step toward Aerosol–gel preparation of active planar wave guides. In this paper, we report on the physical, chemical, optical, microstructural and spectroscopic properties of the multilayer coatings. A new optically active crystalline phase, Er 2 Ti 2 O 7 (ETO), has been identified. This study shows that, depending on the experimental conditions (titanium and erbium content, heat treatment temperature), ETO can be obtained in the form of nanocrystallites dispersed in a transparent amorphous matrix.