The colour tuning of upconversion emission from green to red in NaScF4:Yb3+/Er3+ nanocrystals by adjusting the reaction time

A series of water-soluble NaScF4:Yb3+/Er3+ upconversion nanoparticles (UCNPs) have been synthesized by a facile hydrothermal route. The samples display a high degree of uniformity and crystallization. The upconversion (UC) emissions from green to red in NaScF4:Yb3+/Er3+ nanoparticles are successfully obtained by adjusting the reaction time from 12 h to 2 h. The UC emission peaks at 541 nm, and 652 nm of all the samples excited by 980 nm correspond to the transitions of 4S3/2/2H11/2 → 4I15/2 and 4F9/2 → 4I15/2 of Er3+ions, respectively. The green UC emission at 541 nm decreases while the red emission at 652 nm increases gradually when the reaction time changes from 12 h to 2 h. This work provides a novel and facile way of tuning colour from green to red in NaScF4:Yb3+/Er3+ UCNPs. These water-soluble nanoball structures NaScF4:Yb3+/Er3+ UCNPs promise to be novel biological probes and possess other applications in many fields.