Optical properties of LiAl 5 O 8 :Fe3+film prepared by the sol-gel method

Abstract

ABSTRACTLiA15O8:Fe3 film has been prepared by using the sol—gel method, and the optical properties of the film have beenexamined. X—ray diffraction analysis indicates that (110)—oriented LiA15O8 film is formed when the gel film is heat—treated at 773 K. The X—ray diffraction patterns of the LiAI5O8 films heat—treated above 1173 K manifest diffractionlines assigned to reflections from the (110), (220) and (440) planes. In contrast, only the diffraction lines correspondingto the (220) and (440) planes are observed in the LiAI5O8 film heat—treated below 1073 K. These results suggest that theLiAI5O8 films heat—treated below 1073 K and above 1173 K possess disordered and ordered structures, respectively. Theemission spectra of the LiAI5O8 films obtained by the heat treatment above 1173 K manifest a zero—phonon line ataround 660 nm with vibronic sidebands in the long wavelength region. These emission bands are ascribed to the transi—tion from 'T1(4G) to 6A1(6S) of Fe3 in tetrahedral site in the ordered phase. The LiAl5O8:Fe3 films obtained by the heattreatment below 1 173 K, which contain microcrystals of less than 10 nm, are optically transparent.Keywords: LiAl5O8:Fe3 film, orientation, ordered phase, disordered phase, emission spectrum1. INTRODUCTIONOptically transparent materials doped with transition metal elements are applicable as a solid state laser, a luminescentsolar concentrator, a spectral hole burning device, and so forth. The optical properties of transition metal ions in oxideglasses, which are typical transparent materials, have been studied extensively in the past. In general, the ligand fieldstrength around the transition metal ion in oxide glasses is low and the emission intensity from the oxide glasses is veryweak.17 For instance, the Cr3 ion, which is utilized for the ruby laser, only manifests a Stokes' shifted broad emissionband in the red to infrared region in oxide glasses even at very low temperatures.27 The R—line which corresponds to thetransition from the 2E to 4A2 levels is barely observed in most of the oxide glasses containing Cr3 ions. Hence, from apoint of view of practical applications as fluorescence materials, oxide glasses doped with transition metal ions are inferi—or.One way to obtain a transition metal—doped transparent material which manifests effective emission intensity is tointroduce microcrystalline phases doped with transition metal ions into the glass. The optically transparent materialwhich consists of microcrystals dispersed homogeneously in glass matrix is known as transparent glass—ceramics.8 Thetransparent glass—ceramics containing microcrystals doped with Cr3 and Co2 ions have been prepared mainly with theaim of application to a solid—state laser, a luminescence solar concentrator, and a spectral hole burning device.92° Thecrystallization process, microstructure and optical properties of transparent glass—ceramics containing MgAl2O4:Cr3,ZnAl2O4:Cr3, mullite:Cr3, 3—quartz solid solution doped with Cr3, ZnGa2O4:Cr3, ZnAl2O4:Co2 and LiGa5O8:Co2