Fluorescence of pyrene-doped polystyrene films from room temperature down to 4 K for wavelength-shifting applications

Abstract

In liquid argon-based particle detectors, slow wavelength shifters (WLSs) could be used alongside the common, nanosecond scale, WLS tetraphenyl butadiene (TPB) for background mitigation purposes. At room temperature, pyrene has a moderate fluorescence light yield (LY) and a time constant of the order of hundreds of nanoseconds. In this work, four pyrene-doped polystyrene films with various purities and concentrations were characterized in terms of LY and decay time constants in a range of temperature between 4 K and 300 K under ultraviolet excitation. These films were found to have a LY between 35 and 50% of that of evaporated TPB. All light yields increase when cooling down, while the decays slow down. At room temperature, we observed that pyrene purity is strongly correlated with emission lifetime: highest obtainable purity samples were dominated by decays with emission time constants of ∼ 250-280 ns, and lower purity samples were dominated by an ∼ 80 ns component. One sample was investigated further to better understand the monomer and excimer emissions of pyrene. The excimer-over-monomer intensity ratio decreases when the temperature goes down, with the monomer emission dominating below ∼ 87 K.

Neck Alpha Background Rejection in DEAP-3600 using Pyrene and the Search for Superheavy Dark Matter

“…including the characterization of their mechanical and cryogenic stability, fluorescence decay time constant, emission spectrum, and PLQY is described in [57], [64], and [65]. Based on the characterization of the pyrene-doped polymeric films, the optimal wavelength shifter for coating the DEAP-3600 flowguides was selected to be a film made of polystyrene (PS), doped with 15% pyrene.…”