Ni2+ in Distorted Octahedral Geometry toward High‐Efficiency NIR‐II/III emitter

Ni2+ activated phosphor has attracted wide attention because it can be radiated in near‐infrared (NIR) II‐III region; however, the low external quantum yield (EQY) hinders its further application (most are below 8%). In this work, distortion of crystallographic site strategy is proposed to enhance EQY. LaTiTaO6: 0.004Ni2+ exhibits an NIR emitting spectrum centered at 1450 nm with an EQY of ~ 9.00%, which has been the highest EQY of reported Ni2+ single‐doped phosphor. Distortion degrees of the octahedral geometry in LaTiTaO6 and LaTiTaO6: 0.004Ni2+ changing from 0.038 to 0.047 result in the absorption efficiency of 38.6% due to the breaking of parity forbidden of the d‐d transition, further improving the EQY. Besides, LaTiTaO6: 0.004Ni2+ mixed with LaTiTaO6: 0.04Cr3+ phosphors have demonstrated their application for spectral analysis. This work provides a new idea for constructing efficient NIR‐II to NIR‐III phosphors.