B. G. Potter

Structure and optical properties of rare earth-doped zinc oxyhalide tellurite glasses

Zinc tellurite glasses appear to be excellent candidates for hosting rare earth ions since they provide a low phonon energy environment to minimize non-radiative losses as well as possess good chemical durability and optical properties. The optical behavior of the rare earth ion can be manipulated by modifying its local environment in the glass host. The authors report measurements of the emission lifetime, optical absorption, and vibrational density of states of the glass system (ZnO){sub x}(ZnF{sub 2}){sub y}(TeO{sub 2}){sub 1{minus}x{minus}y}doped (0.1 mol%) with a series of rare earths. Phonon sideband spectroscopy has been successfully employed to probe vibrational structure in the immediate vicinity of the rare earth ion. The authors observe a significant increase in the emission lifetime (from approximately 150 {mu}s to 250 {mu}s) of Nd{sup 3+} with increasing fluorine substitution.

Quantum‐confinement effects in CdTe‐glass composite thin films produced using rf magnetron sputtering

Quantum‐confinement‐induced shifts in the fundamental absorption edge of isolated CdTe crystallites are reported in CdTe‐glass composite thin films produced using a sequential rf magnetron sputtering process employing two separate sputtering sources. Films ranging in thickness from 0.5 to 4.5 μm and containing as much as 30 vol % CdTe have been produced, illustrating the versatility of this technique over a more conventional melting approach. Post‐deposition heat treatments were used to produce average crystallite sizes in the range 46–158 A. An improved fit to theory at larger crystal sizes is found if a cylindrical crystal morphology is assumed. The effective mass of the confined specie, which governs the shift of the absorption edge with crystal size, is found to be 0.20m0 (spherical morphology) and 0.12m0 (cylindrical morphology), both of which are greater than the exciton‐reduced mass in bulk CdTe. The data suggests, therefore, that a non‐negligible Coulomb interaction may still exist in crystals eve...

GeO2SiO2 thin films for planar waveguide applications

Abstract Various thin films of germanium silicate glass with high germania content have been fabricated by a sol-gel method. After densification, these films have a high optical quality and can be used as planar waveguides. The densification behavior of these films was studied by measurements of the index of refraction, as a function of heat treatment temperatures, using ellipsometry. The relationship of refractive index versus GeO2 content follows the additive Lorentz-Lorenz model. Waveguiding Raman spectroscopy suggested the formation of SiOGe linkages in these films without phase segregation. Various waveguide propagation characteristics, at 632.8 nm, were studied using a prism coupling technique. The propagation loss rate of a 50GeO250SiO2 glass waveguide was measured as 3.31 dB/cm.

Photosensitivity of solgel-derived germanosilicate planar waveguides

The effects of controlled atmosphere heat treatments on the photosensitivity and UV absorption of GeO(2)-SiO(2) solgel planar waveguides are presented. Photoinduced refractive-index changes in the samples are deduced from photosensitive grating writing experiments and are found to be of the order of those seen in some fiber experiments. A correlation is seen between the sample sensitivity and the strength of the absorption at 242 nm, providing insight into the possible mechanisms governing photosensitive processes in these materials.

Electro-optical characterization of Pb(Zr,Ti)O3 thin films by waveguide refractometry

Electric field‐induced changes in the extraordinary and ordinary refractive indices of a Pb(Zr0.53Ti0.47)O3 thin film were independently determined using waveguide refractometry. Under an electric field, applied normal to the film plane and corresponding to saturation of the electric polarization, the ratio of the extraordinary to ordinary refractive index change (Δne/Δno) is found to be −4/1, contributing to a net birefringence change [Δ(ne‐no)] of −0.021. Using this technique, both diagonal and off‐diagonal elements of the electro‐optic response tensor describing the macroscopic behavior of the polycrystalline film were accessed, illustrating the importance of this approach in evaluating orientation‐specific electro‐optic characteristics in these films.

Monte Carlo simulation of ferroelectric domain structure and applied field response in two dimensions

A two-dimensional, lattice-Monte Carlo approach, based upon the energy minimization of an ensemble of electric dipoles, was developed to simulate ferroelectric domain behavior. The model utilizes a Hamiltonian for the total energy based upon electrostatic terms involving dipole–dipole interactions, local polarization gradients, and the influence of applied electric fields. The impact of boundary conditions on the domain configurations obtained was also examined. In general, the model exhibits domain structure characteristics consistent with those observed in a tetragonally distorted ferroelectric. The model was also extended to enable the simulation of ferroelectric hysteresis behavior. Simulated hysteresis loops were found to be very similar in appearance to those observed experimentally in actual materials. This qualitative agreement between the simulated hysteresis loop characteristics and real ferroelectric behavior was also confirmed in simulations run over a range of simulation temperatures and appl...

Increased radiative lifetime of rare earth-doped zinc oxyhalide tellurite glasses

We have investigated the structural and optical properties of rare earth-doped zinc tellurite glasses modified by the substitution of ZnF2. Raman and phonon sideband spectroscopies were employed to characterize changes in the glass structure as well as to probe vibrational behavior in the immediate vicinity of the rare earth ion. These measurements are combined with photoluminescence and optical absorption to monitor the effect of halide substitution upon the optical behavior of the rare earth dopant. A substantial increase in the intrinsic radiative lifetime of Nd3+ is observed with increasing halide concentration.

Raman characterization of CdTe nanocrystallites embedded in a glass matrix

Abstracts are not published in this journal

Quantum‐size effects on the band edge of CdTe clusters in glass

The measurement of quantum‐size behavior in semiconductor crystals has been examined through an analysis of the size dependence of the semiconductor’s absorption edge. In past studies, there appeared to be little agreement between theory and experiment for very small crystals. In this paper, the effects of crystal‐size distribution and tunneling of the carrier wave functions into the quantum well barrier are considered. An analysis of the microstructure size and absorption edge of CdTe clusters in a glass matrix is conducted with samples ranging from 0.16 to 0.8 times the exciton Bohr diameter at the Γ point and from 1 to 5 times the exciton Bohr diameter at the L point. Results show fully coupled exciton behavior at the L point and a more complex process at the Γ point. In the latter, the band‐gap energy increase with decreasing cluster size is significantly smaller than that calculated using a model in which the photoexcited carriers are assumed to be confined to a monosize set of clusters bounded by an...

Photoluminescence in Chemical Vapor Deposited ZnS: insight into electronic defects

Photoluminescence spectra taken from chemical vapor deposited (CVD) ZnS are shown to exhibit sub-band-gap emission bands characteristic of isoelectronic oxygen defects. The emission spectra vary spatially with position and orientation with respect to the major axis of CVD growth. These data suggest that a complex set of defects exist in the band gap of CVD ZnS whose structural nature is highly dependent upon local deposition and growth conditions, contributing to inherent heterogeneity in optical behavior throughout the material.