Photon pairs are generated via spontaneous parametric down conversion (SPDC), have a wide and flexbile wavelength tuneability, going from the visible (VIS - 400 nm) to the mid infrared (MIR - 5000 nm) spectral range. We use ppKTP, ppLN, AGS and LGS crystals to access the VIS, NIR and MIR spectral ranges to characterize quantum efficiency, dark counts, dead time of single photon detectors.