The time-gated PL spectra of 6NICz in particular showcase the competition between TADF and phosphorescence, with the intensity of the TADF decreasing and the intensity of the phosphorescence increasing with decreasing temperature (Figure ). In all cases, the phosphorescence at 77 K matches that observed at room temperature, and so the phosphorescence can be assigned to the radiative decay from the T1 state. To ensure that there is no possibility that emission from aggregates contributes to the observed photophysics, we next prepared 0.1 wt% doped films in PMMA. The PL spectra both in air and under vacuum are comparable to the 1 wt% doped film spectra (Figure , black and red lines), with the primary difference being the ratio of the fluorescence to phosphorescence under vacuum. In 4NICz, 5NICz, 6NICz, and 6,10NICz, there is a decrease in the proportion of phosphorescence to fluorescence in the 0.1 wt% doped films compared to the 1 wt% doped films, but in 7NICz this is reversed, with a slight increase in the phosphorescence relative to fluorescence in the 0.1 wt% doped films. The time-gated PL also corresponds well to the 1 wt% doped films in PMMA (Figure ), and so the same biluminescence behaviour is preserved at 0.1 wt% emitter concentration.