David J. Robbins

Luminescent metal complexes. Part 1. Tris-chelates of substituted 2,2′-bipyridyls with ruthenium (II) as dyes for luminescent solar collectors

Ruthenium(II) and osmium(II) complexes of 2,2′-bipyridyls (bipy) and 1,10-phenanthrolines (phen) are identified as feasible dyes for use in luminescent solar collectors. Twenty-seven RuII(bipy)32+ complexes are prepared and the absorption and emission spectra of their solutions in EtOH–MeOH at room temperature are reported. Quantum efficiencies, Which are sensitive to oxygen quenching, vary between 0.002 and 0.306 depending upon substituents. The effect of the medium on the spectral properties of selected compounds has also been investigated. Measured quantum yields of non-aqueous solutions are higher than those for aqueous solutions but lower than for doped plastic films.

Luminescent metal complexes. Part 3. Electrochemical potentials of ground and excited states of ring-substituted 2,2′-bipyridyl and 1,10-phenanthroline tris-complexes of ruthenium

E ½ values for 21 tris-complexes of substituted 2,2′-bipyridyls and 1,10-phenanthrolines with RuII–RuIII in acetonitrile have been measured using cyclic voltammetry. A linear correlation exists between E½ and the Hammett σ constant for data obtained from complexes of 4,4′-and 5,5′-disubstituted 2,2′-bipyridyls. The reduction potential for the couple Ru(ligand)33+–*Ru(ligand)32+, where * refers to the excited state, have been calculated from the E½ values and a combination of data collected from luminescence and magnetic circular dichroism measurements.

Si-based electroluminescence at THz frequencies

Experimental results of electroluminescence in the terahertz gap, at 6 THz (or 40 μm) from Si/SiGe multi quantum well structures, grown by a commercial chemical vapour deposition system are presented. Theoretical simulations were used to design the heterolayer structure and to explain the emission and absorption features. Electrical and materials characterisation is also presented to demonstrate the quality of the heterolayers.

Luminescent metal complexes. Part 5. Luminescence properties of ring-substituted 1,10-phenanthroline tris-complexes of ruthenium(II)

The absorption characteristics, emission spectra, luminescent quantum yields, and lifetimes are reported for 24 ruthenium(II) tris-1,10-phenanthroline complexes in EtOH–MeOH solution. Quantum yields fall between 0.019 and 0.403, the highest values being recorded for complexes substituted at the 4,7-sites with aryl groups. Incorporation of these derivatives into poly(vinyl chloride) film raises the quantum yields leading to values ranging from 0.40 to 0.75.

Magnetic circular dichroism spectra of tris-chelate complexes of 2,2′-bipyridyl and 1,10-phenanthroline with iron(II), ruthenium(II), and osmium(II) at 4.2 K

The magnetic circular dichroism (m.c.d.) spectra, in alcoholic glasses at 4.2 K, are reported for the tris-chelates of 2,2′-bipyridyl and 1,10-phenanthroline of iron(II), ruthenium(II), and osmium(II), including those of the substituted bipyridyl ligands, 4,4′-diphenyl-, 4,4′-diethoxy-, 4,4′-di(ethoxycarbonyl)-, and 5,5′-di(ethoxycarbonyl)-2,2′-bipyridine. The spectra in the region of the spin-allowed metal-to-ligand charge-transfer bands show good resolution and a number of the expected A-terms are apparent. The osmium(II) complexes also show well defined A-terms in the region of the formally spin-forbidden transitions. Calculation of the signs and magnitudes of the A-terms has been carried out using a theoretical model proposed previously. Good agreement is obtained between the experimental results and the theoretical predictions in the case of tris(2,2′-bipyridyl)osmium(II). The relationship between the form of the spectrum of this complex and the others studied is discussed. The m.c.d. spectra of the triplet states do not help to resolve the controversy over the assignment of the luminescing states.

Terahertz Emission From Silicon-Germanium Quantum Cascades

Whilst most present day efforts towards the realisation of a silicon based laser are focused on the near-infrared (telecommunications) wavelengths, one of the most promising technical approaches is that of a silicon-germanium (SiGe) quantum cascade laser (QCL) operating in the far-infrared or terahertz frequency range. Until recently, the terahertz band (1–10 THz) has proved relatively inaccessible for science and engineering applications since it lies above the present upper frequency limit of millimetre wave electronic based oscillators, and below the range of near and mid-infrared solid state lasers and detectors. However, there is currently a great deal of interest in the development of terahertz technology for imaging and sensing applications: terahertz pulsed imaging has been shown to be capable of detecting caries (the precursor of decay) in human teeth [1], and there are also promising signs that the method could be used to detect basal cell carcinoma (a common form of skin cancer) [2]. Many chemical and biological molecules have absorption lines in the THz band, and therefore applications are envisaged in chemical/biological detection and identification. THz imaging is also potentially suitable for baggage/personnel scanning for security applications, where it would provide a low-energy, non-ionising alternative to X-rays.

Towards SiGe Terahertz VCSELs

Asymmetric rolling, in which the circumferential velocities of the upper and lower rolls are different, can give rise to intense plastic shear strains and in turn shear deformation textures through the sheet thickness. The ideal shear deformation texture of fcc metals can be approximated by the <111> // ND and {001}<110> orientations, among which the former improves the deep drawability. The ideal shear deformation texture for bcc metals can be approximated by the Goss {110}<001> and {112}<111> orientations, among which the former improves the magnetic permeability along the <100> directions and is the prime orientation in grain oriented silicon steels. The intense shear strains can result in the grain refinement and hence improve echanical properties. Steel sheets, especially ferritic stainless steel sheets, and luminum alloy sheets may exhibit an undesirable surface roughening known as ridging or roping, when elongated along RD and TD, respectively. The ridging or roping is caused by differently oriented colonies, which are resulted from the <100> oriented columnar structure in ingots or billets, especially for ferritic stainless steels, that is not easily destroyed by the conventional rolling. The breakdown of columnar structure and the grain refinement can be achieved by asymmetric rolling, resulting in a decrease in the ridging problem.

Silicon germanium quantum cascade heterostructures for far-infrared emission

Terahertz (far-infrared) intersubband electroluminescence is reported in p-type Si/SiGe quantum wells and quantum cascade structures. Surface-normal emission (without the aid of a surface grating) from light hole - heavy hole intersubband transitions has been observed for the first time in a quantum cascade device. Edge-emission measurements have also been performed, which show emission from both heavy hole - heavy hole and light hole - heavy hole transitions, and have allowed demonstration of the polarisation dependence of the emitted power, according to the selection rules for the intersubband interactions. The electroluminescence is visible up to temperatures of ~150K, in the multiple quantum well structures, and >=77K in the quantum cascade structure.