Temperature dependent emission spectra of spin excited iodine in crystalline Xe and Kr are presented and analyzed in terms of nonadditive anisotropic pair interactions. In the octahedral trap site, the atomic 2P states split into E,,, and Gsj2 groups of the double valued representation. The fourfold degenerate G,,, state is subject to strong Jahn-Teller instability and further splits by coupling to phonons mto

Investigations are reported on the x-ray scintillation and imaging application of CdTe quantum dots ͑QDs͒ and their polymer nanocomposites. Aqueous CdTe QDs with emissions ranging between 510 and 680 nm were prepared and incorporated into polyvinyl alcohol or polymethyl methacrylate polymer matrices. The x-ray luminescent properties were evaluated and a resolution of 5 lines/mm was obtained from the nanocomposite films. Additionally, the fast decay time, nonafterglow, and superior spectral match to conventional charge coupled devices, show that CdTe QD nanocomposites have high promise for x-ray imaging applications. © 2011 American Institute of Physics. ͓doi:10.1063/1.3589366͔High-performance x-ray phosphor screens are a key device component for applications such as x-ray crystallography and mammography. For example, the current generation of charge coupled devices ͑CCDs͒ based x-ray crystallography detectors are mosaic arrays of individual modules, each consisting of a phosphor screen, to convert incident x-rays to light, a fiber-optic taper to couple the light into a CCD sensor, and the CCD, which converts the light into an electronically readable format. 1,2 However, these x-ray detectors are still not as fast, sensitive, efficient, or have high enough resolution as required by some applications and existing limitations restricts their usefulness in many biological and medical applications. In order to improve the performance of these detectors, x-ray phosphor screens with excellent properties including: high stopping power, high spatial resolution, very fast decay times, minimum afterglow, detector spectral match, and excellent x-ray conversion efficiency are required.In this letter, CdTe quantum dot ͑QD͒ based polymer nanocomposites were studied for x-ray scintillation and imaging applications. QD nanomaterials can be advantageous for x-ray applications compared to traditional phosphors. Current x-ray phosphor screens are made using micron-sized powder phosphors such as Gd 2 O 2 S : Tb, ZnSe:Cu,Cl, or CsI:Tl, which are efficient and bright x-ray converters. 3 They provide good results with regards to efficiency ͑ratio of visible light output to x-ray absorption͒, stopping power ͑x-ray absorption efficiency͒, and time response ͑decay time and afterglow͒. However, large-sized phosphor particles give rise to a great deal of scatter, which limits their spatial resolution ͑minimum distinguishable features in the image͒. There is ample theoretical argument to suggest that nanometer-sized particles, such as QDs, in a transparent polymer-matrix screen will exhibit significantly higher spatial resolution than micron-sized phosphor particles. 4,5 In addition, the fast decay time and nonafterglow features of QDs will ensure faster time response than that of existing powder phosphors. Also, QDs can be made from high-Z and high density compounds such as CdTe, CdHgTe, PbSe, and PbTe to increase stopping power relative to that of low-Z and less-dense phosphor materials. Moreover, the narrow emission band of QDs can be tun...

The gas phase photodissociation of chlorine dioxide has been examined to elucidate its role in the destruction of stratospheric ozone. The existence of the photodissociation channel, OClO + hv → Cl + O2, which could in principle catalyze the destruction of ozone, has recently been reported (E. Rühl et al., 1990). We establish here that the quantum yield of this process, in the spectral range 359–368 nm is less than 5×10−4 and therefore too small to significantly perturb the stratospheric ozone budget.

The electronic spectroscopy of oxygen atoms trapped in solid xenon are reported. Excitation of the solid between 220 and 260 nm leads to two main emissions centered at 3.35 and 1.65 eV, both of which arise from the same upper state. The excitations are assigned to chargetransfer absorptions in interstitial Oh sites; the emitting state, which has a lifetime of 227 ns, is assigned to Xe+O-('xc+). An avoided crossing between the ionic and covalent Ix+ states, and differential solvation of these states, explains the main trends of the spectroscopy of XeO in the gas and condensed phases. Implications regarding ionic and covalent many-body surfaces are discussed.