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A study of the quantum efficiency of the luminescence of gadolinium and terbium in borate glasses and of the energy transfer between these ions is presented. From our measurements of fluorescence decay times, absorption, fluorescence, and excitation spectra, we calculated the fluorescence quantum yield of the 6P7/2 gadolinium and the 5D4 terbium levels on excitation to higher gadolinium and terbium levels, respectively. The energy transfer rates between gadolinium and terbium in borate glasses were calculated on the basis of the above measurements. These measurements were performed for gadolinium and terbium concentrations ranging from 0 to 4 wt%. Our results show that the energy transfer occurs mainly between the 6P7/2 gadolinium level and (5D0, 5H7) terbium levels and is due to a dipole-dipole interaction. It is concluded that the energy transfer between gadolinium and terbium is a phonon assisted process.

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Correlation of SO2 and Fe2+ measurements with new spectral data indicates that the Liebermann-Burchard (L-B) and Zak color reactions for cholesterol have similar oxidative mechanisms, each yielding, as oxidation products, a homologous series of conjugated cholestapolyenes. These studies further suggest that the colored species observed in these two systems are enylic carbonium ions formed by protonation of the parent polyenes. Thus, the red (λmax, 563 nm) product typically measured in the Zak reaction is evidently a cholestatetraenylic cation, and the blue-green product in the L-B reaction (λmax, near 620 nm) is evidently the pentaenylic cation. The effects of rate of carbonium ion formation and sulfuric acid concentration on sensitivity and color stability are discussed. A solvent extraction procedure is described for specifically converting cholesterol to 3,5-cholestadiene. Incorporating this step into the typical L-B method can increase the L-B sensitivity for cholesterol by several fold.

Absorption, excitation, and emission spectra of europium have been measured in metaphosphate glasses, The oscillator strengths of the transitions of the 7Fo and 'F1 levels are calculated and compared with the values for aqueous solutions. The intensities and half-bandwidths of fluorescence from the SDo levels are compared with those of silicate glasses and aqueous solutions. The influence of the crystal fields of the glass 013 the hypersensitive AJ = 2 transition is discussed. The point symmetry of Eu in phosphate glass was found to be C,. The broadening of the spectral lines in glasses and aqueous solutions has been attributed to a multiplicity of sites with the same symmetry and various crystal field parameters.

The use of various organic co mpound s in soluti on and inorganic ions in glasses has• bee n investi • gated as poss ible fluoresce nce Standard Refere nce Mate rials. Emphasis was placed on meas uring physical and chemical paramete rs such as stability, reprodu cibilities of absorbance and fluorescence meas urements , re lative quantum effi ciencies as a fun ction of excitation wavelength , etc., for quinine d erivatives and selected organic co mpounds. A brief discussion is in cluded on th e use of rare earth and non• rare earth in organic ions in glasses as standards.