Time-Correlated Single Photon Counting (TCSPC) Spectroscopy

Ambra Guarnaccio  -


The TCSPC technique allows measuring the fluorescence emission after the molecule excitation with a proper excitation wavelength,(ʎex) (generated by high-frequency pulsed laser radiation) enabling to determine the fluorescence lifetime by the fitting of the resulting decay curve. This technique allows to measure the fluorescence (radiative) emission, ʎem) after the excitation of a sample with a pulsed laser radiation. With periodic excitation, e.g., from a high frequency laser source, it is possible to extend the data collection over multiple cycles of excitation and emission. One can then accept the sparseness of the collected photons and reconstruct the fluorescence decay profile from the multitude of single-photon events collected over many cycles. The reference for the timing is the corresponding excitation pulse triggered by a fast photodiode collection.


  • Available laser sources:
    • Spectra Physics, Spitfire Pro, Ti:Sa Laser: ʎ 800 nm (tunabile con sistema OPA nel range 290-2500 nm); 120 fs; 4 mJ; repetition rate up to 1 KHz;
    • Tsunami: ʎ 800 nm (400 nm by SHG using a BBO crystal); 90 fs, 10 nJ, 80 MHz;
  • Electronic for timing: PicoQuant Pico Harp 300;
  • Fast photodiode: TDA 200;
  • Monochromator: Princeton Instruments ACTON SP2150;
  • Photo-multiplier tube: PicoQuant PMA-C 192-N-M (< (< 180 ps (FWHM))


  • Fluorescence decay (Int. vs Time);
  • Fluorescence anisotropy and in polarization control;
  • Fluorescence 3D maps (time vs ʎem vs Int.) of fluorescence decays over a wide wavelength range of excitation (ʎex 290-2500 nm) and emission (ʎem 230-920 nm).


  • Preferred: diluted solutions(10-4-10-6 M) in organic solvents;

  • Thin films



  • Organic/Inorganic Semiconductors;

  • Thin films/coatings;

  • Nanoparticles.


Case Studies

COUMARIN 500 (C500) fluorescence decay

The study case of C500 has been used in order to evaluate the performance of our experimental setup using a Tsunami (80MHz, ʎex 400 nm BBO SHG). The fit analysis has highlighted that a mono-exponential decay model is useful to describe the radiative fluorescence decay (τ=5.04 ns)registered by exciting a 10-5 M of C500 in EtOH, solution by a 400 nm ultra fast laser source as reported in literature for the same dye system under analysis.

See: Sanjucta, Nad et al., J. Phys. Chem. A, 107, 501 (2003)
DOI: 10.1021/jp021141l


FLUORESCENCE 3D MAP of a short oligothiophene (DTBT) molecule

The experimental setup described for the C500 study case has been used to investigate the fluorescence lifetime related to a solution (10-4 M/CH2Cl2 of a short chain oligothiophene compound useful for organic photovoltaic applications (i.e. the DTBT, 1,3-di(2-thienyl)-2-benzothiophene). The evaluation of the fluorescence lifetime has been the starting point for a much wider comprehension of radiative and non-radiative processes occurring within the excited DTBT systems (by fs laser excitation source) in solution. Indeed, the fluorescence "competes" with non-radiative decay processes studied by FTAS (Femtosecond Transient Absorption Spectroscopy) measurements.

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