Instrument response functions (IRF) in time-domain fluorescence are usually recorded as reflected or scattered excitation light, which is at shorter wavelengths than the observed fluorescence emission. However, its often more appropriate to measure the IRF in the emission spectral region. In this work we show that Rose Bengal water solutions quenched by potassium iodide can be used to measure instrument response functions of single photon detectors in the orange-red wavelength region. We used the quenched RB emission as a reference in time-domain measurements with common detectors and we got practically the same results as with scattering. (C) 2009 Elsevier B.V. All rights reserved.