Angela B. Seddon

Chalcogenide glasses: a review of their preparation, properties and applications

The author provides an update of: glass preparation in bulk, fibre and film form; optical and thermal properties, and potential applications of chalcogenide glasses.

Fabrication and characterization of nanoscale, Er3+-doped, ultratransparent oxy-fluoride glass ceramics

We show that oxy-fluoride glass ceramics, with typical composition, 32(SiO2):9(AlO1.5):31.5(CdF2):18.5(PbF2):5.5(ZnF2): 3.5(ErF3) mol % have potential applications in telecommunications. Upon heat treatment, Er3+ nucleates the growth of the nanocrystalline β-PbF2, which acts as its host. Heat treatment at 440 °C for 5 h and at 390 °C for 3 h gave rise to ∼12 and ∼2.5 nm diameter crystals, respectively. The emission band of Er3+ in the 1.54 μm telecommunications window (4I13/2→4I15/2 transition, at the half-height width) was 75 nm in the former and 90 nm in the latter case, while 4I13/2↔4I15/2 absorption and emission bands became wavelength divergent in both cases. Also in the latter case, the spectrum was flat from 1.53 to 1.56 μm. The evolution of spectral behavior is explained by changes in average site geometry of the Er3+ dopant, related to the α→β phase transition of PbF2, which is stimulated by heat treatment.

Progress in rare-earth-doped mid-infrared fiber lasers.

The progress, and current challenges, in fabricating rare-earth-doped chalcogenide-glass fibers for developing mid-infrared (IR) fiber lasers are reviewed. For the first time a coherent explanation is forwarded for the failure to date to develop a gallium-lanthanum-sulfide glass mid-IR fiber laser. For the more covalent chalcogenide glasses, the importance of optimizing the glass host and glass processing routes in order to minimize non-radiative decay and to avoid rare earth ion clustering and glass devitrification is discussed. For the first time a new idea is explored to explain an additional method of non-radiative depopulation of the excited state in the mid-IR that has not been properly recognized before: that of impurity multiphonon relaxation. Practical characterization of candidate selenide glasses is presented. Potential applications of mid-infrared fiber lasers are suggested.

Near- and mid-infrared spectroscopy of sol–gel derived ormosils: vinyl and phenyl silicates

Abstract The suitability of ormosils as photonic materials was investigated. Vinyl and phenyl silicates were synthesised below 100°C. A detailed assignment of mid-infrared vibrational absorption bands is given. This allowed assignment of overtone and combination bands in the near-infrared region and an assessment of residual water contamination, which is low and can be expelled by evacuation. These ormosils have low intrinsic and extrinsic optical absorption in the visible spectral region and at useful wavelengths in the near-infrared.

A solid state solar cell using sol–gel processed material and a polymer

Abstract We present a heterojunction photovoltaic cell, fabricated from sol–gel TiO2 anatase and poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH–PPV). The solid state cell has a peak power conversion efficiency of 1.6% when illuminated with monochromatic light at 500 nm. At this wavelength the fill factor of the device is 0.67 and the incident photon to current conversion efficiency is 9.5%. The open circuit voltage of the device under these conditions is 0.63 V, similar to the value calculated using capacitance techniques. The anatase TiO2 thin film was prepared by sol–gel processing and dip-coating techniques, whereas the soluble conjugated polymer film, MEH–PPV, was spin coated on top of the TiO2 anatase film. Layer thicknesses of 50 and 80 nm were obtained for TiO2 and MEH–PPV, respectively, and cross section TEM photographs of the TiO2 layer shown the dense nature of the polycrystalline anatase structure with crystallite sizes ranging from 5 to 20 nm.

Transparent Ho3+-doped nano-glass-ceramics for efficient infrared emission

We developed transparent 3.5mol% Ho3+-doped oxyfluoride nano-glass-ceramics, where the Ho3+-dopants dissolve in the 6nm diameter β-PbF2 nanocrystals. The cubic site of Ho3+ and a low vibration frequency of its PbF2 environment result in an intense and 50nm broad emission band I65→I85 of Ho3+ at 1.2μm with a temperature independent lifetime of 1.6ms. Another 40nm broad emission band F55→I65 at 1.47μm with a lifetime of 24μs was also excited, the lifetime of this band increased to 60μs at 77K. These two bands have potential application for optical amplification in telecommunications.

Thulium pumped mid-infrared 0.9-9μm supercontinuum generation in concatenated fluoride and chalcogenide glass fibers.

We theoretically demonstrate a novel approach for generating Mid-InfraRed SuperContinuum (MIR SC) by using concatenated fluoride and chalcogenide glass fibers pumped with a standard pulsed Thulium (Tm) laser (T(FWHM)=3.5ps, P0=20kW, ν(R)=30MHz, and P(avg)=2W). The fluoride fiber SC is generated in 10m of ZBLAN spanning the 0.9-4.1μm SC at the -30dB level. The ZBLAN fiber SC is then coupled into 10cm of As2Se3 chalcogenide Microstructured Optical Fiber (MOF) designed to have a zero-dispersion wavelength (λ(ZDW)) significantly below the 4.1μm InfraRed (IR) edge of the ZBLAN fiber SC, here 3.55μm. This allows the MIR solitons in the ZBLAN fiber SC to couple into anomalous dispersion in the chalcogenide fiber and further redshift out to the fiber loss edge at around 9μm. The final 0.9-9μm SC covers over 3 octaves in the MIR with around 15mW of power converted into the 6-9μm range.

Study of mid-infrared laser action in chalcogenide rare earth doped glass with Dy 3+ , Pr 3+ and Tb 3+

We present a study of chalcogenide glass fiber lasers doped with Dy3+, Pr3+ or Tb3+ that would operate in the mid-infrared wavelength range. A set of chalcogenide glass samples doped with different concentrations of rare earth ions is fabricated. The modeling parameters are directly extracted from FTIR absorption measurements of the fabricated bulk glass samples using Judd-Ofelt, Fuchtbauer–Ladenburg theory and McCumber theory. The modeling results show that, for all the dopants considered, an efficient mid-infrared laser action is possible if optical losses are kept at the level of 1dB/m or below.

High density, non-porous anatase titania thin films for device applications

TEM studies have been performed on 50 nm thick monolayer films of sol-gel derived anatase titania (TiO2). It is found that a dense polycrystalline structure, having low porosity and consisting of nanocrystallites ranging from 5-20 nm in diameter, is the result of a sintering process involving temperature ramping up to 550 °C. Ohmic conduction is believed to be due to almost flat band conditions caused by partial depletion of carriers from the crystallites.

Embossing of chalcogenide glasses: monomode rib optical waveguides in evaporated thin films

Single-mode optical rib waveguides operating at telecommunication wavelengths are successfully patterned via a hot embossing technique in a thermally evaporated chalcogenide glass thin film on a chalcogenide glass substrate. Ellipsometry is used to measure the refractive index dispersion of the pressed film (As(40)Se(60)) and substrate (Ge(17)As(18)Se(65)).