Terbium doped glasses: their optical properties and potential applications

The optical properties of inorganic glasses doped with terbium have been investigated with particular emphasis on silicate glass systems. The effect of increasing terbium concentration on the refractive index of silicate glasses has been investigated and the optical absorption from 0.2 to 40 microns has also been studied. The energy levels of the trivalent terbium ions involved in the various optical processes have been identified by reference to theoretical predictions and spectra in other media. Glasses doped with terbium show intense series of blue and green luminescence emissions when excited by ultra-violet or X-ray radiation. Emissions from the (^5) D (_3) level of the Tb (^3+) ions produce the blue luminescence while the green emission results from transitions from the (^5) D (_4) level. At terbium concentrations above 0.3 mole % the blue emissions are quenched by multipolar transitions from the (^5) D (_3) level to the (^5) d (_4) level. The green emissions are quenched at concentrations above 6 mole % by an exchange-dipole mechanism. The effect of temperature on the emission characteristics has been determined. Intense luminescence persists to temperatures above 500 C in silicate glasses. The reduction in temperature does not greatly change the emission intensity. Inhomogeneous broadening, due to the random nature of the glass matrix, persists even at liquid helium temperatures. Decay rates have been measured at various temperatures with both ultra-violet and X-ray excitation. The effect of other rare earths on the photoluminescence has also been investigated, and a model for the lanthanide ion site is proposed. The thermoluminescence characteristics of terbium doped silicate glasses have also been measured. Increased terbium concentration reduces the glow peak intensity. A model of the mechanism producing thermoluminescence is proposed. Differences between binary (sodium silicate) and ternary (lithium aluminosilicate) glasses, observed in both photo- and thermoluminescence, are discussed. Other optical properties, such as the Faraday Effect and cathodoluminescence, are reviewed in a survey of the literature

Cell free hemoglobin in the fetoplacental circulation: a novel cause of fetal growth restriction?

Cell free hemoglobin impairs vascular function and blood flow in adult cardiovascular disease. In this study, we investigated the hypothesis that free fetal hemoglobin (fHbF) compromises vascular integrity and function in the fetoplacental circulation, contributing to the increased vascular resistance associated with fetal growth restriction (FGR). Women with normal and FGR pregnancies were recruited and their placentas collected freshly postpartum. FGR fetal capillaries showed evidence of erythrocyte vascular packing and extravasation. Fetal cord blood fHbF levels were higher in FGR than in normal pregnancies (P < 0.05) and the elevation of fHbF in relation to heme oxygenase-1 suggests a failure of expected catabolic compensation, which occurs in adults. During ex vivo placental perfusion, pathophysiological fHbF concentrations significantly increased fetal-side microcirculatory resistance (P < 0.05). fHbF sequestered NO in acute and chronic exposure models (P < 0.001), and fHbF-primed placental endothelial cells developed a proinflammatory phenotype, demonstrated by activation of NF-κB pathway, generation of IL-1α and TNF-α (both P < 0.05), uncontrolled angiogenesis, and disruption of endothelial cell flow alignment. Elevated fHbF contributes to increased fetoplacental vascular resistance and impaired endothelial protection. This unrecognized mechanism for fetal compromise offers a novel insight into FGR as well as a potential explanation for associated poor fetal outcomes such as fetal demise and stillbirth

Eleven entries of notes on Hanyu da zidian

An important characteristic of any scintillator is its temporal response to an impulse of radiation. Ideally, the response time for the induced luminescence is much shorter than the time interval between data acquisitions. As the response time approaches this time interval blurring results in the acquired images. The presence of a long secondary decay component is typically referred to as afterglow. In order to avoid conditions under which such blurring may occur, a study of the scintillator’s temporal characteristics is required. This is especially important for x-ray computerized tomography where an object is constantly in motion