The RTP emission of the B-fibers was sensitive to the excitation wavelength: the RTP wavelength changed from 450 nm to 530 nm when the excitation wavelength increased from 240 nm to 360 nm (Fig. ). More interestingly, RTP emission of the B-fibers overlapped with rhodamine B (RhB) absorbance, suggesting the possibility of energy transfer between B-fiber and RhB (Supplementary Fig. ). To test this hypothesis, we immersed the B-fibers in RhB solution and the as-obtained B-fiber/RhB system exhibited red afterglow emission upon UV excitation, matching the fluorescence spectra of RhB (Fig. ). The lifetime of red afterglow emission from RhB in the B-fiber/RhB was 73.59 ms (Supplementary Fig. ).