Measuring scatter with a cryogenic probe and an ICCD camera: recording absorption spectra in Shpol'skii matrixes and fluorescence quantum yields in glassy solvents.

Recording absorption spectra via transmittance through frozen matrixes is a challenging task. The main reason is the difficulty in overcoming the strong scattering light reaching the detector. This is particularly true when thick samples are necessary for recording absorption spectra of weak oscillators. In the case of strongly fluorescent compounds, additional errors in absorbance measurements arise from the emission reaching the detector, which might have an intensity comparable to that of the transmitted light. This article presents a fundamentally different approach to low-temperature absorption measurements as the sought for information is the intensity of laser excitation returning from the frozen sample to the ICCD. Laser excitation is collected with the aid of a cryogenic fiber optic probe. The feasibility of our approach is demonstrated with single-site and multiple-site Shpol'skii systems. The 4.2 K absorption spectra show excellent agreement with their literature counterparts recorded via transmittance with closed-cycle cryogenators. Fluorescence quantum yields measured at room temperature compare well to experimental data acquired in our laboratory via classical methodology. Similar agreement is observed between 77 K fluorescence quantum yields and previously reported data acquired with classical methodology. We then extend our approach to generate original data on fluorescence quantum yields at 4.2 K.