Linac 2100cd

Cherenkov emission was induced by a linear accelerator (Varian LINAC 2100CD, Palo Alto, California). The imaging system consisted of a time-gated intensified CCD camera (ICCD, PI-MAX4 1024i, Princeton Instruments) and a commercial lens (Canon EF 135 mm f/2L USM). The camera was focused on a mirror that reflected the imaging field $\sim 1\mathrm{m}$ away. The time-gated ICCD camera was synchronized to the radiation pulses ( $\sim 3.25\mu \mathrm{s}$ duration and 360 Hz repetition rate) with the intensifier set as $\times 100$ and turned on at a 4.26- or $1000\text{-}\mu \mathrm{s}$ gate delay following each radiation pulse for phosphorescence or background measurement, and luminescence generated during $85.60\text{-}\mu \mathrm{s}$ gate width (PtG4 and MM2), or $7.77\mu \mathrm{s}$ [ $\mathrm{Ir}{(\mathrm{btb})}_2(\mathrm{acac})$ ] was integrated via this ICCD. Images of the luminescence at different delay times between LINAC pulse and phosphorescence emission were acquired to construct emission lifetime. To maximize signal and minimize background interference, the room lights were shut off throughout these studies, and all lights in the room were masked off with black cloth and black tape.