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We show that all possible binary combinations of molecules from four different families of organics - a diamine derivative, N,N′-bis(3methylphenyl)-N,N′-diphenylbenzidine, an oxidiazole derivative, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, a substituted thiophene dioxide, 2,5-bis(trimethylsilyl thiophene)-1,1-dioxide, and poly(9-vinylcarbazole) - produce white or near-white emission. We suggest that this is due to exciplex formation, and that this is likely to be a general phenomenon for blends of blue-emitting aromatic organics. This implies that films of spin-coated blends of blue-emitting organics represent a general, simple, and cheap route to white-emitting organic light-emitting diodes.

Thin films of indium tin oxide [(ITO), ${\mathrm{In}}_{2}{\mathrm{O}}_{3}:\mathrm{Sn}$] have been grown by reactive electron beam deposition. Annealing in ultrahigh vacuum and, subsequently, in situ room temperature scanning tunneling microscopy (STM) and spectroscopy have been carried out. STM images before annealing show the film composed of grains with sizes around $30\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ while images of samples annealed at $423\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $573\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ indicate that these grains coalesce with sizes of $60--80\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Scanning tunneling spectroscopy (STS) curves for the samples in the three different conditions indicate the existence of a small band gap with Fermi level position pinned in the center of the band gap. Optical reflectance and transmittance measurements have been performed in order to deduce optical and electronic properties. STS combined with optical data interpreted with Drude theory shows that the samples have a direct band gap of $3.5\phantom{\rule{0.3em}{0ex}}(\ifmmode\pm\else\textpm\fi{}0.1)\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and an indirect band gap of $2.1\phantom{\rule{0.3em}{0ex}}(\ifmmode\pm\else\textpm\fi{}0.2)\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$.

We report on white electroluminescence (EL) emission from a single-layer light-emitting diode based on a binary blend of organic soluble blue-emitting molecules, i.e., a diamine derivative and a substituted thiophene-1,1-dioxide. Weakly voltage-dependent white color, of coordinates (0.39, 0.40) according to the standard of the Commission Internationale de l’Eclairage, is obtained from the superposition of the blue emission from the donor and a low-energy peak due to a charge-transfer complex between the two molecules (exciplex). The EL spectrum is broader and more structured than the photoluminescence one: this could be due to the activation of exciplexes with different conformations as inferred from quantum-chemistry calculations.