Observation of the critical regime near Anderson localization of light

Diffusive transport is among the most common phenomena in nature [1]. However, as predicted by Anderson [2], diffusion may break down due to interference. This transition from diffusive transport to localization of waves should occur for any type of classical or quantum wave in any media as long as the wavelength becomes comparable to the transport mean free path $\ell^*$ [3]. The signatures of localization and those of absorption, or bound states, can however be similar, such that an unequivocal proof of the existence of wave localization in disordered bulk materials is still lacking. Here we present measurements of time resolved non-classical diffusion of visible light in strongly scattering samples, which cannot be explained by absorption, sample geometry or reduction in transport velocity. Deviations from classical diffusion increase strongly with decreasing $\ell^*$ as expected for a phase transition. This constitutes an experimental realization of the critical regime in the approach to Anderson localization.Comment: 5 pages, 4 figure

Magneto-optical effects on the emission of self-trapped exciton perturbed by Na impurity in CsI:Na crystal

The tunnelling recombination of trapped holes (VK) and electron (Na0)pairs in CsI:Na crystal was studied by optical detection of ESR and magnetic CD in the 420 nm emission. A model explains the data and allows determine of the tunnelling probabilities

Synthesis of ferroelectric perovskites through aqueous-solution techniques

The hydrolysis of niobates in aqueous solutions has been applied to the coprecipitation of PbNb2/3Mg1/303 leading to a low temperature synthesis of this ferroelectric relaxor ceramic. The effect of hydrolysis conditions - such as the concentration of bases and acids used, their rates of addition and the nature of the precursors salts - is described. The perovskite phase appears after heating at 350°C and is obtained as a pure phase at 800°C after heat treatment for 1 h. Relaxor ferroelectric ceramics with a high dielectric constant can be obtained by sintering at 1000°C The process has been also applied to the synthesis of other relaxor ceramic compositions such as PZN (PbNb2/3Zn1/303) and PFN (PbNb1/2Fe1/203) compounds

Optical properties of F centers in KCN crystal

Absorption, excitation and emission spectra of F centers in KCN were measured between 4.5-175 K. Due to the cubic to orthorhombic structural phase transition at 168 K, the F band splits into 3 components. Their properties in the antiferroelectric phase (T <83 K) are explained by an internal Stark effect due to the local electric field. The single emission band has a decay time of 21.5 ns at 4.5 K

Radio and thermoluminescence studies in CsI doped with F centers

Radioluminescence, thermoluminescence, and u.v. excitation measurements in CsI additively colored crystals showed a new luminescent component at 2.5 eV. This is attributed to the radiative recombination of Vk centers with F centers. Another new component at 2.72 eV was observed only under uv excitation of 5.14 eV. This is related to the radiative recombination of localized excitons at F+ center sites (&#945; band)

EPR optical detection of F centre pairs in alkali halides. - I : Pumping cycle kinetics and characteristics of the resonances

The EPR of F centres in the ground and excited states was optically detected in the following alkali halide crystals: NaCl, KF, KCl, KBr, KI, RbBr, and RbI. A decrease of the radiative quantum efficiency of the F centre luminescence was observed when microwave transitions were induced between the spin levels. The mechanism responsible for this effect was an electronic tunnelling through the crystal field potential; the electron in the relaxed excited state of an F centre (F~*) is transferred nonradiatively to another nearby F centre in its ground state (F0), and leads to the momentary formation of an ƒ¿ and an F\u27 centre. Such a process is a function of the total spin of the F~*-F0 pair. The role played by the paired centres was confirmed by measurements at different F centre concentration. Moreover, at high optical excitation pumping rates, the population of the intermediate complexes (F\u27-ƒ¿) is large enough to allow an estimation of the rate of the reverse process F\u27 + ƒ¿ \u27¨ F0 + F0