Preparation and characterization of holmium doped ZIF-8 nanocrystals for white light emitting phosphors

We report on the generation of white light from Ho-doped ZIF-8 nanocrystals synthesized by a simple wet chemical technique at room temperature. The influence of Holmium (Ho) concentration and heat treatment on both structural and optical responses has been investigated. The crystal structure and morphology of as-synthesized (As) and post-thermal annealed (TA) nanocrystals have been examined using X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). In addition, the thermal stability and bond structure have been studied via Thermogravimetric analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR), respectively. Moreover, the photoluminescence (PL) measurements were performed using two excitation wavelengths: 445 nm and 355 nm. The XRD and TEM evidenced the sodalite nanocrystalline nature of the samples. The TGA and FTIR analyses demonstrated the degradation behavior of ZIF-8 due to the incorporation of Ho ions and thermal calcination. The PL results showed intense luminescence response, in particular, from the heat-treated samples. Furthermore, the PL exhibited a naked-eye observed white light emission. This was attributed to the structural modifications induced by the dopant and thermal treatment. Our findings could be used as a guideline towards the potential application of lanthanide-doped MOFs (ZIF-8) in light-emitting purposes.