Uniformly Dispersed Nanoparticles in Modified Polyimides Exhibiting High Thermal Stability and Bright Emissions in the Telecommunication Window

Excellent optically active photonic composites are indispensable for designing polymeric waveguide amplifiers which may spur the development of the next generation of high efficiency communication systems. However, due to the poor thermal stability, low light transmittance, low solids loading and non-uniform nanoparticle dispersion, most existing materials and composites are unable to meet the waveguide requirements for operation at high-power needed to achieve high optical gain. Thus, 30 nm-sized core–shell NaYF4:Yb,Er,Ce@NaYF4 nanoparticles coated with oleic acid (OA) were designed to emit strongly at ∼1530 nm which is within the low loss telecommunication window of 1300–1650 nm which most communication devices operate in. By engineering the nanoparticle interfacial interactions within the solution and polymer matrices, nanoparticle agglomeration is prevented to limit any undesired scattering losses. In this work, we report the synthesis of a series of polyimide (PI)-based matrices that were modified to improve their compatibility with the nanoparticle’s surface chemistry and at the same time exhibit excellent thermal stability and optical transparency. Specifically, the carboxyl group was introduced to improve the dispersion of nanoparticles at high solids loading and also the solubility of PIs in solvents required for composite film formation. After incorporating the nanoparticles together with the modified polyimide matrix, a photonic composite film with excellent thermal stability (Tg = 314 °C, Tdegrade = 383 °C), high solids loading (∼10.2 vol %), and bright emissions (1530 nm) within the telecommunication window was fabricated.