Proof of crystal-field-perturbation-enhanced luminescence of lanthanide-doped nanocrystals through interstitial H+ doping

Crystal-field perturbation is theoretically the most direct and effective method of achieving highly efficient photoluminescence from trivalent lanthanide (Ln 3+ ) ions through breaking the parity-forbidden nature of their 4 f -transitions. However, exerting such crystal-field perturbation remains an arduous task even in well-developed Ln 3+ -doped luminescent nanocrystals (NCs). Herein, we report crystal-field perturbation through interstitial H + -doping in orthorhombic-phase NaMgF 3 :Ln 3+ NCs and achieve a three-orders-of-magnitude emission amplification without a distinct lattice distortion. Mechanistic studies reveal that the interstitial H + ions perturb the local charge density distribution, leading to anisotropic polarization of the F − ligand, which affects the highly symmetric Ln 3+ -substituted [MgF 6 ] 4− octahedral clusters. This effectively alleviates the parity-forbidden selective rule to enhance the 4 f –4  f radiative transition rate of the Ln 3+ emitter and is directly corroborated by the apparent shortening of the radiative recombination lifetime. The interstitially H + -doped NaMgF 3 :Yb/Er NCs are successfully used as bioimaging agents for real-time vascular imaging. These findings provide concrete evidence for crystal-field perturbation effects and promote the design of Ln 3+ -doped luminescent NCs with high brightness.