3-Hydroxyflavone-based wavelength shifting systems for near UV optical sensors

In this work the dye molecule 3-hydroxyflavone (3-HF) is employed as wavelength shifter in order to enlarge the sensitive spectral window of silicon photodiodes, owing to its high Stokes’ shift which allows to convert near UV light into visible light at about 530 nm. This fluorescence property arises from the excited-state intramolecular proton transfer (ESIPT) process which leads to the formation of a phototautomeric form of the molecule after excitation. Transparent monolithic and thin film samples of hybrid organic–inorganic silica xerogels containing dispersed 3-HF molecules are produced. Emission and excitation spectra of 3HF are also measured with a UV-Vis spectrofluorimeter in order to characterize the ESIPT process in the different systems. The samples are then applied to overlay the detection area of a silicon photodetector in order to measure the sensitivity enhancement obtained with a 3-HF-based wavelength-shifting material.