White-Light Emission in Zeolitic Imidazolate Framework Glasses

Some zeolitic imidazolate frameworks (ZIFs) represent a new family of glass formers, with hitherto unknown photonic functionalities. In this work, we report the discovery of broadband white light emission in ZIF-62, achieved through a vitrification-pressurization-annealing strategy. In this strategy, visible (blue) light emission was realized after the vitrification of ZIF-62, subsequently enhanced and broadened upon pressurization. Additionally, a sharp redshift (37 nm) of the emission peak occurred in pressurized ZIF-62 glass as the annealing temperature exceeded a critical annealing temperature (1.07T_g). This implies that the photoluminescence of ZIF-62 can be precisely tailored. The photoluminescence quantum yield of ZIF-62 glass reached 12.2% after annealing at 1.13T_g for 30 min. The origin of the observed phenomena was revealed by conducting structural analyses. Based on the annealed ZIF-62 glass with the best photoluminescent performance, a white light-emitting diode (LED) was fabricated, which exhibited a luminous efficacy of 4.2 lm/W and a high operational stability, i.e., retaining 36.8% of the efficacy after 72 h of operation. This work demonstrated the feasibility of the development of one-component white LEDs by utilizing the annealed ZIF-62 glass.