No abstract

No abstract

No abstract

Abstract. -The luminescence of MgO single crystals has been investigated using a scanning electron microscope (SEM) with a detection system for spectroscopic cathodoluminescence (CL) studies. The corrected CL spectrum of MgO consists of a large blue band with a maximum at 460 nm and a broad red emission with a dominant 722 nm peak. Annealing treatments in air, carbon monoxide or hydrogen change the spectra considerably. Oxidation divides the blue band into a number of peaks and shoulders and finally eliminates the deformation-induced peak entirely but has no effect on the shape or position of the red emission. In contrast, heating in Tiydrogen produces a sharpening of the broad red luminescence into six peaks, whilst the blue band remains unaffected. A similar effect was observed for carbon monoxide treatment except that very long annealing times completely eliminated the red peaks and replaced them by a new broad band at 645 nm.1. Introduction. -Our earlier observations [1] showed that deformed MgO has a corrected cathodoluminescence (CL) spectrum containing two broad bands which are well separated in wavelength (~ 300 nm apart). Monochromatic CL SEM micrographs taken at the blue 466 nm (2.66 eV) peak of the first band showed that the emission was localized at the slip planes. The red emission is a composite of overlapping bands with a prominent 770 nm (1.61 eV) peak and remains unaffected by crystal deformation. Monochromatic (one wavelength) micrographs taken at the red wavelength still show a homogeneous emission distribution after deformation.

[P late 6.] Introductory.It is well known that the limits of the series and the separation of doublets and triplets, which occur in the line spectra of chemically related elements, are intimately connected with the atomic weights of the elements involved. I t seemed reasonable to suppose that numerical relations might also exist in the case of band spectra, and the present paper gives an account of an investi gation undertaken to determine possible relations among the band spectra of similar compounds of different elements. Previous work by other observers suggested the fluorides of the alkaline earth metals as a suitable group of compounds for the purpose in view. In the first instance a more complete survey of the spectra of these compounds was made, and several bands in addition to those previously described have been observed. These new bands have proved of considerable service in the identification of corresponding bands in the different spectra, and details relating to them are accordingly included in the paper.The beautiful bands of CaF2, SrF2, and BaF2 were first observed in the flame spectra by Mitscherlieh* as far back as 1862, but no systematic measurements were made until 1905, when observations of the bands of these compounds in the visible region were made by Fabryf with a spectroscope of not very large dispersion. Measurements of the same spectra from photo graphic plates were first made by RoschJ and further measures were subse quently made by Leopold^ in the case of SrF2, and by George|| in the case of BaF2.The ultra-violet bands of these compounds were studied by OlmstedlT in 1906, but the bands of the fluorides were not completely separated from those of the oxides, which in this region are closely grouped with those of the fluorides, particularly in calcium and strontium.