Solid–liquid phase equilibrium and mixing thermodynamic analysis of coumarin in binary solvent mixtures

The solubility of coumarin in three aqueous solvent mixtures (methanol + water, ethanol + water and acetone + water) was experimentally determined by a gravimetric method at atmospheric pressure. The experimental solubility data were fitted using the modified Apelblat equation, non-random two-liquid (NRTL) equation, the combined nearly ideal binary solvent/Redlich–Kister equation and the Jouyban?Acree equation, respectively. All the equations were proven to be able to correlate the experimental data, and the modified Apelblat equation could obtain better correlation results than the other three models. The solubility of coumarin increases with increase in temperature. At the same temperature, the solubility increases with increase in mole fraction of organic solvents except for the ethanol–water system which shows a unimodal curve. In addition, the apparent thermodynamic properties of the mixing process were calculated based on the NRTL model and the experimental solubility data.     

Radiant-energy detection by?Ba?Cu?O thin films

High T_c superconducting films offer promise as fast sensitive detectors of microwave and infrared. A high T_c superconducting transition-edge bolometer was fabricated from Y–Ba–Cu–O thin film on a (100) SrTiO₃ substrate, and tested at about the T_c midpoint using a 500 K blackbody source. In this initial work only NEP=5×10^–8W/Hz^1/2 was achieved with a large time constant caused by rather thick substrate. The sensitive element was put in the vacuum chamber of a liquid nitrogen metal cryostat for three weeks and through ten cold-hot cycles (80 K-300 K), the sensitivity of the bolometor kept repeatable. Some future work is also discussed.     

Surface-plasmon-polariton assisted diffraction in periodic subwavelength holes of metal films with reduced interplane coupling

Metal films grown on an Si wafer perforated with a periodic array of subwavelength holes have been fabricated and anomalous enhanced transmission in the midinfrared regime has been observed. High order transmission peaks up to Si(2,2) are clearly revealed due to the large dielectric constant contrast of the dielectrics at the opposite interfaces. The Si(1,1) peak splits at oblique incidence both in TE and TM polarization, which confirms that anomalous enhanced transmission is a surface-plasmon-polariton (SPP) assisted diffraction phenomenon. Theoretical transmission spectra agree excellently with the experimental results and confirm the role of SPP diffraction by the lattice.     

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.