We removed approximately 100% of clathrated oxygen ions from the crystallographic cages in a single crystal of 12CaO.7Al2O3, leading to the formation of high-density (approximately 2 x 10(21) cm-3) electrons highly localized in the cages. The resulting electron forms a structure that we interpret as an F+ center and migrates throughout the crystal by hopping to a neighboring cage with conductivity approximately 100 siemens per centimeter, demonstrating that the encaged electron behaves as an anion. The electron anions couple antiferromagnetically with each other, forming a diamagnetic pair or singlet bipolaron. The resulting [Ca24Al28O64]4+(4e-) may be regarded as a thermally and chemically stable single crystalline "electride."

Al 28 O 64 ] 4+ (4e -). -The title compound is synthesized by removal of nearly 100% of clathrated oxygen ions from the crystallographic cages of a single crystal of 12CaO·7Al2O3, or [Ca24Al28O64] 4+ (2O 2-), which is achieved by treatment with calcium metal shots at 700°C and leads to the formation of high-density electrons highly localized in the cages. The resulting electron forms a structure that is interpreted as an F + center and migrates throughout the crystal by hopping to a neighboring cage with a conductivity of about 100 S/cm, behaving as an anion. The electron anions couple antiferromagnetically with each other, forming a diamagnetic pair or singlet bipolaron. The title compound may be regarded as a thermally and chemically stable single crystalline "electride". The stabilization of numerous bound electrons could provide new approaches to preparing conductive materials with unusual optical or magnetic properties.In addition, such materials may find application as low-temperature electron emitters. -(MATSUISHI, S.; TODA, Y.; MIYAKAWA, M.; HAYASHI, K.; KAMIYA, T.; HIRANO, M.; TANAKA, I.; HOSONO*, H.; Science (Washington, D. C.) 301 (2003) 5633, 626-629; Mater. Struct. Lab., Tokyo Inst. Technol., Midori, Yokohama 226, Japan; Eng.) -W. Pewestorf 44-015

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Electrides are ionic compounds in which electrons act as anions. These compounds are expected to have interesting properties arising from their exotic structure. The fatal drawbacks of the thermal and chemical instability of organic electrides were resolved by the synthesis of a room temperature (RT) stable electride using single crystalline 12CaO.7Al2O3 (C12A7) with a nanoporous structure and the chemical treatments for a long duration. However, an innovative fabrication method is obviously required for practical applications such as cold electron-emitter and thermionic devices. Herein we report a simple synthesis for polycrystalline C12A7 electrides with a moderate electronic conductivity via a strongly reducing C12A7 "melt", i.e., direct solidification of the melt or crystallization of the transparent glass. Generation of carrier electrons and precipitation of the C12A7 phase from the strongly reducing melt and glass are likely associated with the incorporation of carbon-related anions for stabilizing the C12A7 phase and keeping the mobile electrons in C12A7. These findings will be broadly utilized for applications by mass production in a desired shape and dimension, facilitating the research of electrides.

12CaO‚7Al 2 O 3 electride (C12A7:e -) is a promising material for the cathode of organic light-emitting diodes (OLEDs), because it has a low work function (φ WF ) 2.4 eV), comparable to metal potassium, and good chemical/thermal stability in an ambient atmosphere. This study examines interfacial electronic structures between C12A7:eand tris-8-hydroxyquinoline aluminum (Alq 3 ) by ultraviolet photoelectron spectroscopy, finding that a low electron-injection barrier of 0.6 eV, which is approximately half of the value for the Al/LiF/Alq 3 interface with the lowest injection barrier, is achieved when the interface is formed on the C12A7:efilm surface obtained by using vacuum annealing and subsequent He plasma treatment. This treatment yields little change in the surface chemical composition and retains a low φ WF value (3.1 eV) of C12A7:e -. These results suggest that C12A7:ehas high potential as an efficient electron-injection electrode for OLEDs.

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Carrier injection properties including threshold voltages of inverted top-emission organic light-emitting diodes (ITOLED) were improved by applying room temperature stable electride [Ca 24 Al 28 O 64 ] 4+ (4e -) (C12A7:e -), which has a low work function of ∼2.4 eV, and a p-type degenerated semiconductor Cu 2-x Se to bottom cathode and top anode buffer layers, respectively. The formation of a low-barrier electron injection contact between C12A7:eand tris(8-hydroxyqunoline)aluminum (Alq 3 ) is demonstrated by the current-voltage characteristics of electron-only devices, as well as by photoelectron spectroscopy. The threshold voltage of the ITOLED is reduced by changing the bottom cathode from Al to C12A7:efrom 9 to 7.6 V at 10 mA cm -2 . A 5 nm thick Cu 2-x Se top anode buffer layer, deposited at room temperature, reduced the threshold voltage further to ∼2 V. The luminance efficiency of ITOLED with a Cu 2-x Se buffer layer is nearly twice as large as that without the buffer layer. We emphasize that developing new electrode materials is an effective means to improve the performance of not only OLED but also other new optoelectronic devices.

Thin films of a new transparent oxide semiconductor 12CaO·7Al2O3 consisting of subnanometer‐sized cages (see Figure inset) have been fabricated, and their light‐induced insulator–conductor conversion is described. Proton implantation at a fluence of 1 × 1018 cm–2 followed by UV‐light irradiation increases the electrical conductivity by more than eleven orders of magnitude to the largest value ∼ 10 S cm–1 (see Figure). The conducting state is erasable by heating.