Determination of photoluminescence quantum yields in dilute solution using non-monochromatic excitation light

The photoluminescence (PL) quantum yields (QYs) of fluorophores in dilute solutions can be determined fluorimetrically according to the comparative method employing standards of known PLQY. This method has recently been demonstrated to become more robust when the absorption of the excitation light and the PL emission are measured simultaneously using a transmitted light detector integrated in the fluorimeter. Herein, aided by fiber-coupled spectroscopic equipment and computerized data processing, we elaborate on this method by measuring the full corrected intensity spectrum of the excitation light transmitted through the sample. This further releases constraints on the monochromatic character of the excitation light and enables the use of broad-band excitation sources such as light-emitting diodes (LEDs). Furthermore, the protocol includes measurements at increasing dye concentration, rigorously verifying the required proportionality between absorbed and emitted light intensities. The PLQYs of solutions of fluorophores determined using the new method are in close agreement with published values.