| Summary: | Abstract
Efficient upconversion (UC)–downshifting (DS), dual-mode-emitting NaGdF4:Yb,Tm/NaGdF4:Tb/NaYF4 core/shell/shell (C/S/S) nanophosphors (NPs) were synthesized. The UC luminescence color changed from blue to sky blue after doping Tb3+ into NaGdF4 shell because Tb3+ emission peaks via 5D4 → 7FJ transition were observed with Tm3+ emission peaks via 1D2 → 3F4 and 1G4 → 3H6 transitions through the energy migration UC process of Yb3+ → Tm3+ → Gd3+ → Tb3+. Upon increasing the Tb3+ concentration in the NaGdF4 shell from 5 to 15%, the Commission Internationale de l’Éclairage (CIE) color coordinates changed from (0.2188, 0.2390) to (0.2616, 0.3654). When NaGdF4:Yb(49%),Tm(1%)/NaGdF4:Tb(15%)/NaYF4 NPs were excited using 273 nm ultraviolet light, the C/S/S NPs exhibited bright green light with CIE color coordinates of (0.3354, 0.5090) as a result of energy transfer from Gd3+ to Tb3+. These bright UC–DS, dual-mode-emitting C/S/S NPs could be applied in various applications, including multiplexed imaging and anticounterfeiting.
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