Pulsed-source time-resolved phosphorimetry: comparison of a commercial gated photomultiplier with a specially wired ungated photomultiplier.

A common problem encountered in recording delayed light emission is that the signal of interest is preceded by a much more intense signal arising from prompt fluorescence. When a photomultiplier tube (PMT) is used as the photosensor in a pulsed-source phosphorimeter, two options are open to an experimenter who finds mechanical shutters inconvenient or impracticable and photon counting inappropriate: apply an electronic gate that suppresses the PMT gain for a brief period, or use a wiring scheme that enables the PMT to quickly regain normal operation after an intense burst of prompt emission. The performance of a squirrel-cage PMT that operates in the latter mode is compared with a new gateable PMT (Hamamatsu H11526 series) with a minimum gate time of 100 ns. The two detectors are found to provide practically the same temporal record of the delayed emission, but the ungated PMT is slightly superior in terms of recovery time and signal-to-noise ratio.