Li+ co-doping induced phase transition as an efficient strategy to enhance upconversion of La2Zr2O7:Er,Yb nanoparticles

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The structural phase transition of materials is one of the most active research areas of solid state and materials chemistry in which atomic rearrangements tune fundamental pysochemical properties during the transition. In most cases, such transition requires high temperature, high pressure, or chemical doping. However, phase transition of complex metal oxides such as La2Zr2O7 has not been studied to enhance the upconversion (UC) and downconversion luminescence of their rare-earth doped nanoparticles (NPs) to meet the demand of their broad applications in solar cells, bioimaging, water purification, etc. In this work, we have successfully co-doped Li+ into La2Zr2O7:Er,Yb NPs to achieve phase transition from ideal ordered pyrochlore (OP) to disordered fluorite (DF) structure. We have confirmed this phase transition to endow UC enhancement from these NPs under 980 nm excitation. Specifically, the UC enhancement of the green and red emissions are 14- and 18-fold, respectively. Meanwhile, DFT calculations indicated that the position of Li atoms with respect to Er doping plays a decisive role in dictating the relative stability of DF and OP structures. To sum, it is expected that the idea provided in this work by realizing and understanding doping induced phase transition to enhance down/upconversion luminescence of NPs can be extended to other metal oxide systems.


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Journal of Luminescence