Characterization of a binary system composed of luminescent quantum dots for liquid scintillation.

Scintillation dosimetry has evolved towards utilizing 3D liquid dosimeters to perform quality assurance verification of complex treatment configuration for photon, electron and proton beams. However, most of the fluorophores utilized in these dosimeters are alike and present limitations. This study aims to establish the profile of CdSe colloidal quantum dots (cQDs) that were given the role of the fluorophore in a binary liquid scintillation system. We chose to investigate the cQDs because of their wide absorption spectrum, the tunability of their absorption and emission spectra with respect to their size and composition, and their ability to function as an effective energy transfer intermediate. The scintillation intensity and spectral response of three organic solvent-based liquid cQD dispersions have been investigated upon irradiation with kV and MV photon beams. The solvents used to disperse the cQDs were hexane, toluene and linear alkylbenzene. The scintillation efficiency of the cQD dispersions has proven to be dependent on the nature of the solvent, the alkylbenzene cQD liquid dispersion having the brightest light emission of the three solutions, for an equivalent deposited dose in the scintillator. Its light output was found to reach a tenth of the light intensity of a commercial liquid scintillator, Ultima Gold, irradiated under the same conditions. This cQD dispersion also demonstrated a remarkable energy transfer to the cQDs, only 5% of its intensity being due to Cherenkov light production in the solvent. Overall, these results indicate that the alkylbenzene cQD liquid dispersion could be the best choice for a potential cQD-based liquid scintillator.

Whispering gallery mode sensing with a dual frequency comb probe.

Silica microspheres are probed with a dual comb interferometry setup. The impulse responses of these microresonators are measured with a temporal resolution smaller than 400 fs over more than 200 ps. The amplitudes and phases of the impulse responses are interpreted as providing sensing information. The more familiar transmission spectra corresponding to the measured impulse responses are also calculated and shown. Sensing is demonstrated by varying the concentration of isopropanol in de-ionized water surrounding the microsphere and by binding bovine serum albumin on the silanized microsphere surface.