The alumina-based compound, 12CaO.7Al O , is a ceramic material with a unique cage-like lattice. Such a structure has enabled scientists to extract various new characteristics from this compound, most of which were unknown until quite recently. This compound has the ability to incorporate different anionic species and even electrons to the empty space inside its cages, thereby changing from an insulator into a conductive oxide. The cage walls can also incorporate different rare earth phosphor elements producing an oxide-based phosphor. All these characteristics are obtained without a significant change in the structure of the lattice. It is, therefore, reasonable to expect that this compound will receive attention as a potential material for display applications. This review article presents recent investigations into the application of 12CaO.7Al O ceramic in various display devices, the challenges, opportunities and possible areas of future investigation into the development of this naturally abundant and environmental friendly material in the field of display.

Abstract:An optimized sol-gel process has now been developed to produce homogeneous thin films of calcium aluminate binary 12CaO.7Al2O3 compound, 12CaO.7Al2O3, on magnesium oxide substrates via spin coating. Fourier transform infrared (FTIR) and Raman spectroscopies have been employed to investigate the effect of annealing temperature and duration on the phase transformations in the films. Heat treatment at 13000C under air atmosphere for 2 hours produced single-phase 12CaO.7Al2O3 films. However, annealing at a lower temperature of 11000C in air for a period of 4 hours in total resulted in the crystallization of 5CaO.3Al2O3 rather than 12CaO.7Al2O3. The Xray photoelectron spectrum of the thin film annealed at 13000C corresponds to the binding energies of C12A7 compound. The annealing temperature of 13000C for 2 hours is found to be sufficient for formulating single phase calcia-alumina binary films in correct stoichiometric ratio of 12:7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 While the fabrication of C12A7 single crystal and polycrystalline bulk has been studied extensively during the last few years, studies on the fabrication of C12A7 thin films are rather limited. The thin film fabrication techniques include pulsed laser deposition and sol-gel method, and magnesium oxide (MgO) single crystal is used as the substrate. A heat treatment temperature of 1100 o C in air atmosphere has been suggested for the crystallization of amorphous thin films prepared via pulsed laser deposition [7,8], while this temperature is mentioned to be too low for the crystallization of the sol-gel derived films [9]. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems CorporationThe fabrication of C12A7 thin films via sol-gel technique has been previously reported employing ethyl acetoacetate (EAA) and aluminium sec-butoxide (ASB) as a chelating agent and the main precursor of aluminium oxide, respectively in the molar ratio of 1:1 in an ethanol solvent.Hydrochloric acid (HCl) was used as the pH regulator [10,11]. However, our initial attempt in the deposition of C12A7 thin films on the MgO substrates using this recipe resulted in the formation of discontinuous films with dendritic growth behaviour. Therefore, the solution recipe was modified in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 3 order to increase the homogeneity and continuity of the films. Highly stable spreading solutions for spin coating were obtained using the modified recipe without the need for the addition of acid. This article presents the Fourier transform infrared (FTIR) and Raman spectroscopy investigations into the effect of heat treatm...

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Optical absorption into 6 mm thick sol-gel derived films, annealed at 1300°C of 12CaOÁ7Al 2 O 3 calcium aluminate binary compound on MgOh100i single crystal substrates was studied at temperatures ranging from room temperature to 300°C. Experimental data were analysed in both Tauc and Urbach regions. The optical band gap decreased from 4.088 eV at 25°C to 4.051 eV at 300°C, while Urbach energy increased from 0.191 eV at 25°C to 0.257 eV at 300°C. The relationship between the optical band gap and the Urbach energy at different temperatures showed an almost linear relationship from which the theoretical values of 4.156 and 0.065 eV were evaluated for the band gap energy and Urbach energy of a 12CaOÁ7Al 2 O 3 crystal with zero structural disorder at 0 K.

Optical constants refractive index and extinction coefficient of sol-gel processed polycrystalline 12CaOÁ7Al 2 O 3 (C12A7) thin films with crystallite grain of 57 nm in size have been determined from optical transmittance and reflectance spectra experimentally obtained at normal incidence and the averaged value of refractive index below the band edge was found to be *2.15. The dispersion relation between refractive index and incident wavelength was examined in terms of both Cauchy-Sellmeier and single-effective oscillator models. The relation between refractive index and band gap energy at different temperatures in the range of 25-300°C was studied. The refractive index showed a positive temperature dependency in the studied temperature range.