Improved Quantum Yield and Excellent Luminescence Stability of Europium-Incorporated Polymeric Hydrogen-Bonded Heptazine Frameworks Due to an Efficient Hydrogen-Bonding Effect

Two of the most persistent challenges for the high-end application of luminescent lanthanide (Ln) compounds are a low quantum yield and luminescence quenching caused by a liquid medium. In this work, a type of polymeric hydrogen-bonded heptazine framework is developed incorporating trivalent europium ions (P-HHF-Eu) via a low-cost and facile low-temperature thermal condensation reaction. Structural characterization clearly reveals that the solid-phase pyrolyzation reaction results in the formation of P-HHF-Eu. Using time-resolved and steady state photoluminescence (PL) spectroscopies, the photophysics and photochemistry of P-HHF-Eu at different hydration degrees are investigated and the role of hydrogen bonding in the significant enhancement of the emission properties is demonstrated. Furthermore, the P-HHF-Eu particles suspended in polyvinyl alcohol hydrogel exhibit excellent luminescence stability with a high PL quantum yield of up to ≈46% and wavelength responsive color-tunable emission, which holds potential for security applications.