The device with cD of 1.5 wt% in TSPO1 host presented narrow violet emission with a maximum at lEL of 411 nm (FWHM = 37 nm) and a shoulder at 428 nm, which are assigned as vibronic bands. The EL matches well the PL of the film at the same cD (lPL = 410 nm, FWHM = 38 nm, 1.5 wt% in TSPO1). At 3 wt% doping concentration, the lEL is nearly unchanged at 412 nm compared to the EL of the 1.5 wt% device; however, the FWHM increased slightly to 41 nm and the shoulder at 428 nm is more pronounced. The lEL of the device with cD of 6.0 wt% is essentially the same (412 nm); however, there is significant broadening of the EL (FWHM = 47 nm) due to the more pronounced shoulder at 428 nm.