Julian R. Sprague

Highly efficient band‐edge emission from InP quantum dots

High quality InP quantum dots with diameters ranging from 25 to 45 A, have been prepared; these quantum dots (QDs) show high quantum yields for band‐edge photoluminescence (lowest energy HOMO‐LUMO transition). The wavelength of the blue‐shifted band‐edge emission ranges from about 575 to 730 nm depending on QD size. The quantum yield for photoluminescence is 30% at 300 K and 60% at 10 K; the multiexponential decay of this emission exhibits lifetimes ranging from 5 to 50 ns. Deep red‐shifted emission due to trapping of carriers in defect states on the QD surface which exhibits lifetimes above 500 ns, has been eliminated by treating the QDs with a dilute solution of HF or NH4F.

Observation of the quantum confined ground state in InP quantum dots at 300 K

Colloidal suspensions of InP quantum dots (diameters 25 and 35 A) show steplike absorption spectra which are blue‐shifted by about 1 eV with respect to bulk material. Time resolved femtosecond spectroscopy at room temperature identifies the first quantum confined state. The nonlinear bleaching signal rises within 300 fs and persists longer than 200 ps.

Low-Temperature Photophysics of Permethylated n-Heptasilane: The Borderline Between Excitation Localization and Delocalization in a Conjugated Chain

The delocalization of electronic excitation in fully saturated molecules plays an important role in determining their photophysical and photochemical properties. Probably the best known example of saturated structures with extensive σ delocalization are the polysilanes, (RR’Si)n, saturated polymers with a silicon backbone, whose valence σσ* absorption lies in the near UV region [1]. For examples of computational studies, see ref [2]. They show a variety of interesting optical properties, such as thermochromism and solvatochromism, which result from the sensitivity of their electronic structure to conformational changes. They have high third-order hyperpolarizability, are photosensitive, and show promise as photolithographic materials. They have high hole conductivity, which is useful in xerography, etc.

Synthesis and Characterization of GaP, InP, and GaInP2 Quantum Dots

Although excellent progress has been made in the preparation and characterization of quantum dots (QDs) made from II-VI compounds, Si, oxides (Ti, In, Cu, W), and iodides (Hg, Pb, Bi); the preparation of high-quality QDs of III-V semiconductors has proven to be problematic.1–8 Here, we report the synthesis and properties of excellent quality binary III-V InP and GaP colloidal QDs, and the ternary III-V QD, GaInP2.9,10