Linear tunable NIR emission via selective doping of Ni2+ ion into ZnX2O4 (X=Al, Ga, Cr) spinel matrix

Adjusted crystal fields can lead to new hybrid materials with promising optical performance. Transition metal ions (TMIs) with d-d electron transitions are sensitive to their surroundings and can be ideal candidates for crystal field research. Herein, we have selected single Ni2+-doped spinel oxide nanocrystals as a model system to systematically explore luminescence mechanisms in different crystal fields. Ni2+-doped ZnAl2O4, ZnGa2O4, and ZnCr2O4 nanospinels with broad near-infrared (NIR) emission bands fully cover the second biological window (1100–1400 nm). We have developed a ZnX2O4 (X = Al, Ga or Cr) (ZXO) spinel framework system using a melting-evaporation procedure, and the whole fabrication period only required 20 min. By changing X ions in the ZXO matrix framework, linear tunable photoluminescence was successfully realized. A sample with a mixed phase of ZnAl2O4 and ZnCr2O4 (ZACO) was also prepared using the same method, and ultrabroadband emissions ranging from 1050-1550 nm were detected. It is valuable to further explore the combinations based on these frameworks to realize tunable emission spectra. Fundamental research on the physical processes will open a new gateway for further research of TMI-doped nanocrystals with promising luminescence properties and broaden the applications to a variety of areas, especially in the biomedical field.