U.V. Absorption Band in Ge‐Doped Sodalite Powders

Abstract

A bright green luminescence, with an emission bandpeak at 5250A and an excitation bandpeak at 3465A, has been reported for germanium-doped sodalite powders. This article reports the results of an investigation of the properties of u.v. absorption band at 3450A that is shown to be responsible for the luminescence. A settled slide technique was used to prepare samples so that small variations in the absorption band could be detected. Experimental results are presented that show the effect of the hydrogen annealing temperature, hydrogen annealing time, and F-center creation on the u.v. absorption band intensity. The results indicate a definite relationship between the u.v. absorption band and the luminescence. The results of the coloration experiments show that the luminescent centers are associated with thermally erasable F-centers while they are independent of photoerasable F-centers. The u.v. band was found to exist in sodalite: C1, Br, and I. While the band intensities differ for those powders, the peak wavelengths are exactly the same. Possible models for both coloration and luminescence are discussed.The luminescent properties of germanium-doped synthetic sodalite powders have been reported by Todd (1, 2). The luminescence is characterized by an emission bandpeak at 5250A and an excitation bandpeak at 3465A. Todd studied the effect of the hydrogen annealing temperature, the hydrogen annealing time, and F-center creation on the luminescent intensity. Information regarding the number of luminescent centers was obtained indirectly rather than by direct experimental observation. The intensity of the luminescence generated within the colored powders was calculated using data obtained from measurements of observed luminescence and diffuse reflectance spectra (2). That study found that F-center creation by electron beam coloration greatly reduces the observed luminescence. This reduction results partially from the absorption of generated luminescence by F-centers while further reduction results from actual quenching of luminescent centers. The quenching was shown to be associated with the creation of thermally erasable F-centers while the creation of optically erasable Fcenters did not cause quenching.This article reports the observation of a u.v. absorption band at 3450A in germanium-doped sodalite powders. The purpose of this study was to determine if this band represents the absorption due to the luminescent centers reported earlier (2). If that were the case, one could directly observe the behavior of the luminescent centers under various experimental conditions rather than use indirect mathematical calculations to obtain the results. A technique for detecting small variations in the u.v. absorption spectra of sodalite powders is described. This technique is used to determine the effect of the hydrogen annealing temperature, hydrogen annealing time, and F-center creation on the u.v. absorption band intensity. The results of these experiments are compared to those reported by Todd (2). Experimental Material prepar...

Titanium–Germoxy Precursor Route to Germanium-Modified Epoxidation Catalysts with Enhanced Activity

“…However, the solid-state diffuse-reflectance ultraviolet–visible (DRUV–visible) spectrum of 1 displayed two distinct absorptions at λ max values of 223 and 261 nm. The former is likely due to the previously mentioned O → Ti LMCT, while the latter lies in the region of germanium absorption observed in doped sodalite powders and mesoporous silica treated with germanium, as well as for i Pr 3 GeOH (Figure S1b of the Supporting Information, trace b).…”

“…These tetrahedral Ti(IV) sites are responsible for the observed catalytic activity, as already described well in the literature. − Spectra of TiGe 3 SBA15( x ) and TiGe 3 SBA15( x )-O 2 catalysts contained an additional band near 250 nm, the intensity of which increased with titanium loading. This band is presumably due to the presence of germanium in the samples, and not due to larger titanium oxide domains, because the DRUV–vis spectrum of complex 1 also exhibits a band in this region [λ max = 261 nm (Figure )] and other germanium-containing materials display similar absorptions. , The fact that this band at 250 nm exists in both TiGe 3 SBA15( x ) and TiGe 3 SBA15( x )-O 2 suggests that even after calcination the structure around the Ti is maintained and the Ti–O–Ge linkage persists. XAS studies also confirm that during the grafting process, the tetrahedral environment about Ti is primarily maintained.…”

Effect of Various Chemical Substitutions on the Physical Properties of Cathodochromic Sodalite

“…Sodalite samples used in this investigation were grown in the form of powder by the hydrothermal method (11). Chemicals were combined according to the equation 6NaOH + 6xSiO2 + 6(1 -x)GeO2 + 3A1203 + 2NaZ Na0Al~(SixGelx)6024 9 2NaZ + 3H20 [1] 9 Si where Z is C1, Br, I, or a combination of two of them and x is the atomic percent of silicon. The resulting powders were identified as sodalite [Na6A16(Si~Gel x)~O24 • 2NAZI by x-ray powder diffraction techniques.…”

“…The interest in cathodochromic materials for storage display tubes has increased recently, mainly because of the unusual cathodochromic properties of sodalite (1)(2)(3)(4)(5). These materials exhibit a change of color when exposed to ultraviolet radiation or to excitation by an electron beam.…”

“…These vacancies are generated by thermally sensitizing the material in a specific environment. Various annealing atmospheres have been used to sensitize sodalite (1)(2)(3)(4)(5)10). All the materials studied in this investigation were annealed in vacuum between 650 ~ and 950~…”