Controllable multi-color upconversion in glass ceramics through engineering crystal lattice distortion

Lanthanide-doped up-conversion (UC) materials with color tunable property show promising application in many fields, such as biological imaging, optical multiplexing, and information security. Although great efforts have been devoted to regulate UC emission color via modifying chemical composition, crystal structure, or external stimuli condition, it is remain a daunting challenge to develop a general strategy that probably suitable for various lanthanide-doped nano-systems. Herein, we verify the cross-relaxation possibility between sensitizer Yb 3+ and activator Er 3+ as well as Er 3+ - Er 3+ pairs can be well modified by engineering the crystal lattice distortion of matrix, leading to the evident UC emission color variations. Specifically, with incorporating Al 3+ or Ca 2+ ions into the Yb/Er co-doped BaF 2 nanocrystals (NCs) contained glass ceramics (GCs), the contraction of the crystal lattice lead to the change of UC emission color from green to red. On the contrary, the high laser excitation power results in the lattice expansion of the Al 3+ -doped BaF 2 :Yb/Er GCs at different Yb 3+ concentration as well as Al 3+ doped CaF 2 GCs, which leads to the greatly increased green-to-red ratio. These multi-color UC GCs show potential application in anti-counterfeiting filed. Our results open up a general avenue for the control of UC emission color via engineering crystal lattice distortion.