Color Control in π-Conjugated Organic Polymers for Use in Electrochromic Devices

Transparent conductors as solar energy materials: A panoramic review

Synthesis, Luminescent Properties, and Biomedical Applications Shili Gai,†,‡ Chunxia Li,† Piaoping Yang,*,‡ and Jun Lin*,† †State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China ‡Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, Harbin Engineering University, Harbin, 150001, P. R. China

Recent Progress in Rare Earth Micro/Nanocrystals: Soft Chemical Synthesis, Luminescent Properties, and Biomedical Applications

Electrochromic (EC) materials are able to change their optical properties, reversibly and persistently, by the application of an electrical voltage. These materials can be integrated in multilayer devices capable of modulating the optical transmittance between widely separated extrema. We first review the recent literature on inorganic EC materials and point out that today's research is focused on tungsten oxide (colouring under charge insertion) and nickel oxide (colouring under charge extraction). The properties of thin films of these materials are then discussed in detail with foci on recent results from two comprehensive investigations in the authors' laboratory. A logical exposition is obtained by covering, in sequence, structural features, thin film deposition (by sputtering), electronic band structure, and ion diffusion. A novel conceptual model is given for structural characteristics of amorphous W oxide films, based on notions of defects in the ideal amorphous state. It is also shown that the conduction band density of states is obtainable from simple electrochemical chronopotentiometry. Ion intercalation causes the charge-compensating electrons to enter localized states, implying that the optical absorption underlying the electrochromism can be described as ensuing from transitions between occupied and empty localized conduction band states. A fully quantitative theory of such transitions is not available, but the optical absorption can be modeled more phenomenologically as due to a superposition of transitions between different charge states of the W ions (6+, 5+, and 4+). The Ni oxide films were found to have a porous structure comprised of small grains. The data are consistent with EC coloration being a surface phenomenon, most likely confined to the outer parts of the grains. Initial electrochemical cycling was found to transform hydrated Ni oxide into hydroxide and oxy-hydroxide phases on the grain surfaces. Electrochromism in thus stabilized films is consistent with reversible changes between Ni hydroxide and oxy-hydroxide, in accordance with the Bode reaction scheme. An extension of this model is put forward to account for changes of NiO to Ni2O3. It was demonstrated that electrochromism is associated solely with proton transfer. Data on chemical diffusion coefficients are interpreted for polycrystalline W oxide and Ni oxide in terms of the lattice gas model with interaction. The later part of this review is of a more technological and applications oriented character and is based on the fact that EC devices with large optical modulation can be accomplished essentially by connecting W-oxide-based and Ni-oxide-based films through a layer serving as a pure ion conductor. Specifically, we treat methods to enhance the bleached-state transmittance by mixing the Ni oxide with other oxides characterized by wide band gaps, and we also discuss pre-assembly charge insertion and extraction by facile gas treatments of the films, as well as practical device manufacturing and device testing. Here the emphasis is on novel flexible polyester-foil-based devices. The final part deals with applications with emphasis on architectural “smart” windows capable of achieving improved indoor comfort jointly with significant energy savings due to lowered demands for space cooling. Eyewear applications are touched upon as well.

/pdf/electrochromics-for-smart-windows-thin-films-of-tungsten-aw0rai8h60.pdf

Electrochromics for smart windows: thin films of tungsten oxide and nickel oxide, and devices based on these

Because fossil fuels are becoming scarce and because of the expected climate change, our standard of living can only be maintained by a significant increase in energy efficiency. Large amounts of energy are consumed for lighting and during operation of displays. Thus, the targets are the development of economical light sources like white-light-emitting diodes and display panels with enhanced efficiency. Solar energy is converted into electricity by solar cells, and their efficiency must be improved considerably. A possible contribution might be delivered by phosphors which allow the conversion of thermal radiation into electrical energy. Although the target of energy efficiency is very important, we must not overlook that medical imaging diagnostic methods require efficient and sensitive detectors. For the solution of these central questions, inorganic solid-state materials doped with rare-earth ions are very promising and are therefore in the focus of current research activities.

Recent Developments in the Field of Inorganic Phosphors

A review is presented of research and development of inorganic scintillators for position-sensitive thermal-neutron detectors to be used at new spallation neutron sources.

Inorganic thermal-neutron scintillators

Instead of the usual sputtered anhydrous tungsten oxide thin films, a powder of monohydrated tungsten oxide (WO3.H2O) was used for the making of an electrochromic infrared emissivity modulator. The WO3.H2O powder was embedded in a porous plastic matrix before being laminated with other appropriate layers of the battery-like device, leading then to a complete flexible emissivity modulator. The widely open structure of the hydrated tungsten oxide makes lithium intercalation easier, which is particularly suitable for the realization of plasticized devices. Compared to a classical battery assembly, a porous plastic graphite layer laminated with a conductive grid was sandwiched between the WO3.H2O and the electrolyte layers. Such an original device allowed both a perfect uniformity in current collection and a sufficient porosity for the liquid electrolyte displacement. The complete device demonstrated a satisfying electrochemical behavior under 1 mV/s potential sweeps, allowing the insertion of a large amount of lithium ions into the WO3.H2O structure. Hemispherical reflectance measurements were carried out both over the VIS/NIR (0.4–2.5 μm) and the mid-infrared (2.5–25 μm) spectral ranges. Reflectance over the 2.5–25 μm spectral range was found to switch from 2% to 32% upon intercalation of 0.65 Li per tungsten. This value is comparable to previous literature results obtained for rigid devices.

Flexible electrochromic reflectance device based on tungsten oxide for infrared emissivity control

Luminescence and scintillation properties of Cs2LiYCl6:Ce were further investigated. Core-valence (CV) luminescence characterized by an excitation band above 14 eV and a 2 ns fast and broad emission band was found. Light yields and decay times under γ excitation were studied for various Ce concentrations. The 0.1% Ce-doped Cs2LiYCl6 was further examined under thermal neutron irradiation. It showed a very high light yield of 70500 photons/neutron. Furthermore the pulse shape for thermal neutrons is different from that for γ-rays which gives the ability of neutron/γ-pulse shape discrimination.

Luminescence and scintillation properties of CS2LiYCl6:Ce3+ for γ and neutron detection

The thermal neutron detection properties of Cs/sub 2/LiYCl/sub 6/:0.1%Ce/sup 3+/ and Cs/sub 2/LiYBr/sub 6/:1%Ce/sup 3+/ single crystals are presented. The compounds show high scintillation photon yields of 70 000 and 88 200 photons emitted per absorbed thermal neutron, respectively. Events caused by primary electrons with energy below 2.9 and 3.4 MeV, respectively, can be separated from neutron-induced events by pulse-height discrimination. For Cs/sub 2/LiYCl/sub 6/:0.1Ce/sup 3+/, due to the presence of a 4-ns fast core-valence luminescence, thermal neutrons and gamma rays can also be discriminated by means of the shape of the scintillation pulse. The main part of the scintillation pulse in Cs/sub 2/LiYCl/sub 6/:0.1%Ce/sup 3+/ is relatively slow, however, Cs/sub 2/LiYBr/sub 6/:1%Ce/sup 3+/ has a relatively intense component with /spl tau/=85;ns decay time.

/pdf/new-thermal-neutron-scintillators-cs-sub-2-liycl-sub-6-ce-4ns9lrh63c.pdf

New thermal neutron scintillators: Cs/sub 2/LiYCl/sub 6/:Ce/sup 3+/ and Cs/sub 2/LiYBr/sub 6/:Ce/sup 3+/

LaI 3 :Ce 3+ has the smallest band gap in the LaX 3 :Ce 3+ (X=F, Cl, Br, I) series and hence a potentially higher scintillation yield. The luminescence properties of LaI 3 :Ce were investigated by means of optical, X-ray, and γ-ray excitation. Unexpectedly, the compound is a poor scintillator at room temperature but presents good scintillation properties for temperatures below 100 K where Ce 3+ emission is observed peaking at 452 and 502 nm with a yield of ∼16 000 photons/MeV. The drastic thermal quenching of luminescence is explained by the proximity of the Ce 3+ lowest 5d excited state to the host conduction band. Autoionization of Ce 3+ therefore prevents any scintillation effect at room temperature. The positions of Ce 3+ levels relative to the host bands were estimated.

/pdf/luminescence-and-scintillation-properties-of-the-small-band-50935rxke4.pdf

Aurélie Bessière

Papers

Inorganic thermal-neutron scintillators

Flexible electrochromic reflectance device based on tungsten oxide for infrared emissivity control

Luminescence and scintillation properties of CS2LiYCl6:Ce3+ for γ and neutron detection

New thermal neutron scintillators: Cs/sub 2/LiYCl/sub 6/:Ce/sup 3+/ and Cs/sub 2/LiYBr/sub 6/:Ce/sup 3+/

Luminescence and scintillation properties of the small band gap compound LaI3:Ce3+