In time-of-flight PET, coincidence time resolution (CTR) of gamma ray detection is essential, with the recent aim of reaching better than 10 ps CTR [1]. Prompt photon emission, e.g. Cherenkov radiation in BGO crystals, has been heralded as a solution to this conundrum. However, Cherenkov detection has low photon yield, prompting high photon detection efficiency and low dark count rate, while achieving fast response with high single-photon time resolution (SPTR) in detectors [2].