Optical Gain Switching by Thermo-Responsive Light-Emitting Nanofibers through Moisture Sorption Swelling

The development of intelligent photonic systems made of stimuli-responsive materials, i.e., with features tunable and switchable by environmental signals, is gaining increasing attention. Here, the study reports on switchable optical gain based on complex arrays of nanofibers made of thermo-responsive poly(2-n-propyl-2-oxazoline), incorporating a blue-emitting chromophore. The fluorescent component endows the nanofibers with optical gain in addition to the moisture absorption capability of the polymer. Light amplification is found with temperature- and humidity-dependent excitation threshold. The threshold value is halved close to the polymer cloud point temperature, enabling reversible switching of the emission intensity upon temperature change. Waveguiding analysis by back-focal plane imaging on individual fibers allows the switching mechanisms to be rationalized, in terms of moisture sorption swelling-induced morphological changes. These responsive light-emitting nanofibers may find application in a novel class of lasers with dynamically-controlled properties, environmentally-switchable optoelectronics, and smart sensors.