New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

Direct sample fraction deposition using electrospray in narrow-bore size-exclusion chromatography/matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for polymer characterization

A direct sample fraction deposition method was developed for off-line size-exclusion chromatography (SEC)/matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. By using electrospray, the SEC eluent, together with a suitable matrix solution added coaxially, was directly deposited on the MALDI plate. Owing to the formation of very small droplets in electrospray, solvent evaporation is much faster. The fractionation volume in narrow-bore SEC, which can directly be collected in one MALDI spot, can easily be optimized in the range of a few microlitres. In addition, fairly homogeneous sample spots were obtained. The possible influence of composition variation of the SEC effluent on the analytical results using direct fraction deposition was investigated; no substantial effects were observed. The applicability of the method was demonstrated by characterizing a broad poly(methyl methacrylate) sample. Copyright 2000 John Wiley & Sons, Ltd.     

A quartz crystal microbalance sensor for the detection of formic acid vapors

A new quartz crystal microbalance sensor is developed to determine formic acid at low concentrations. Four previously selected polymers with acid-base characteristics were tested as possible coatings. Polyoxyethylene bis [amine] presented the best results. The sensor is rapid, sensitive [0.67 Hz/(mg/m3)], and reversible at low concentrations. The detection limit for formic acid (7.2 mg/m3) is comparable with the short term exposure limit and the threshold limit values. It presents a fast mechanical response to pressure changes, so that it can be quickly used in different environments and situations. The sensor also shows a good stability in a temperature range typical of work atmospheres (16-36 degrees C). It has a wide linear range (7.2-911.2 mg/m3) and a long useful time. It is also applicable to other low molecular mass carboxylic acids such as acetic acid.     

A quartz crystal microbalance sensor for the detection of formic acid vapors

A new quartz crystal microbalance sensor is developed to determine formic acid at low concentrations. Four previously selected polymers with acid–base characteristics were tested as possible coatings. Polyoxyethylene bis [amine] presented the best results. The sensor is rapid, sensitive [0.67 Hz/(mg/m³)], and reversible at low concentrations. The detection limit for formic acid (7.2 mg/m³) is comparable with the short term exposure limit and the threshold limit values. It presents a fast mechanical response to pressure changes, so that it can be quickly used in different environments and situations. The sensor also shows a good stability in a temperature range typical of work atmospheres (16–36 °C). It has a wide linear range (7.2–911.2 mg/m³) and a long useful time. It is also applicable to other low molecular mass carboxylic acids such as acetic acid. Received: 26 September 2000 / Revised: 8 February 2001 / Accepted: 12 February 2001