Encapsulating carbon quantum dot and organic dye in multi-shell nanostructured MOFs for use in white light-emitting diode

Encapsulating luminescence units into porous metal-organic frameworks to obtain white-light emission has attracted much attention because of their high designability and excellent color-tuning flexibility. In this study, two types of luminescence units with different emission color coverage, namely green-emitting carbon quantum dots (CQDs) and red-emitting rhodamine B (RhB) molecules, were encapsulated into porous ZIF-8 to obtain the yellow-emitting composite phosphor for use in white light-emitting diodes (LEDs). Single-phase single-shell CQDs&RhB@ZIF-82, as well as single-phase multi-shell CQDs@ZIF-82@RhB@ZIF-82, were fabricated and fine-tuned (by varying the amount of accommodated CQDs and RhB) so that the emitted color is near that of the commercial yellow-emitting phosphor. The multi-shell CQDs@ZIF-82@RhB@ZIF-82 has much better luminescence efficiency than that of the single-shell one. This is because the multi-shell structure provides a much larger separation distance of the encapsulated guest units, diminishing the energy-transfer-caused efficiency decrease. It is also shown that a bright source of white light can be realized by coating the CQDs@ZIF-82@RhB@ZIF-82 nanocomposite on a commercial blue (460 nm) LED chip.