Glenn A. Crosby

Bio: Glenn A. Crosby is an academic researcher. The author has contributed to research in topics: Transition metal & Absorption spectroscopy. The author has an hindex of 6, co-authored 6 publications receiving 4630 citations.

Measurement of two-photon excitation cross sections of molecular fluorophores with data from 690 to 1050 nm

Abstract: Measurements of two-photon fluorescence excitation (TPE) spectra are presented for 11 common molecular fluorophores in the excitation wavelength range 690 nm < λ < 1050 nm. Results of excitation by ∼100-fs pulses of a mode-locked Ti:sapphire laser are corroborated by single-mode cw Ti:sapphire excitation data in the range 710 nm < λ < 840 nm. Absolute values of the TPE cross section for Rhodamine B and Fluorescein are obtained by comparison with one-photon-excited fluorescence, assuming equal emission quantum efficiencies. TPE action cross sections for the other nine fluorophores are also determined. No differences between one-photon- and two-photon-excited fluorescence emission spectra are found. TPE emission spectra are independent of excitation wavelength. With both pulsed and cw excitation the fluorescence emission intensities are strictly proportional to the square of the excitation intensity to within ±4% for excitation intensities sufficiently below excited-state saturation.

Fluorescence Lifetime Measurements and Biological Imaging

Abstract: When a molecule absorbs a photon of appropriate energy, a chain of photophysical events ensues, such as internal conversion or vibrational relaxation (loss of energy in the absence of light emission), fluorescence, intersystem crossing (from singlet state to a triplet state) and phosphorescence, as shown in the Jablonski diagram for organic molecules (Fig. 1). Each of the processes occurs with a certain probability, characterized by decay rate constants (k). It can be shown that the average length of time τ for the set of molecules to decay from one state to another is reciprocally proportional to the rate of decay: τ = 1/k. This average length of time is called the mean lifetime, or simply lifetime. It can also be shown that the lifetime of a photophysical process is the time required by a population of N electronically excited molecules to be reduced by a factor of e. Correspondingly, the fluorescence lifetime is the time required by a population of excited fluorophores to decrease exponentially to N/e via the loss of energy through fluorescence and other non-radiative processes. The lifetime of photophycal processes vary significantly from tens of femotoseconds for internal conversion1,2 to nanoseconds for fluorescence and microseconds or seconds for phosphorescence.1 Open in a separate window Figure 1 Jablonski diagram and a timescale of photophysical processes for organic molecules.

Thiol-capping of cdte nanocrystals: an alternative to organometallic synthetic routes

Abstract: New approaches to synthesize photostable thiol-capped CdTe nanocrystals are reported. Post-preparative size-selective precipitation and selective photochemical etching have been developed as methods providing an increase of photoluminescence quantum efficiency of the nanocrystals of up to 40%. Some advantages of thiol-capping in comparison to conventional organometallic syntheses of quantum dots are discussed.

Excimers and Exciplexes of Conjugated Polymers

Abstract: Observations of intermolecular excimers in several pi-conjugated polymers and exciplexes of these polymers with tris(p-tolyl) amine are reported. It is shown that the luminescence of conjugated polymer thin films originates from excimer emission and that the generally low quantum yield is the result of self-quenching. Thus, in sufficiently dilute solution, the "single-chain" emission has a quantum yield of unity. Exciplex luminescence and exciplex-mediated charge photogeneration have much higher quantum yields than the excimer-mediated photophysical processes. These results provide a basis for understanding and controlling the photophysics of conjugated polymers in terms of supramolecular structure and morphology.