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Upconversion emission tuning from green to red in Yb3+/Ho3+-codoped NaYF4 nanocrystals by tridoping with Ce3+ ions
Guanying Chen1, Haichun Liu, Gabriel Somesfalean
1Department of Physics, Harbin Institute of Technology, 150001 Harbin, People's Republic of China.
Abstract:
Upconversion (UC) emission tuning from green to red in monodisperse NaYF(4):Yb(3+)/Ho(3+) nanocrystals was successfully achieved by tridoping with Ce(3+) ions under diode laser excitation of 970 nm. It is proposed that two efficient cross-relaxation processes, 5S2/5F4(Ho) + 2F(5/2)(Ce) --> 5F5(Ho) + 2F(7/2)(Ce) and 5I6(Ho) + 2F(5/2)(Ce) --> 5I7(Ho) + 2F(7/2)(Ce)between Ho(3+) and Ce(3+) ions, have been employed to select UC pathways to tune the UC radiation. Theoretical investigations based on steady-state equations demonstrate the proposed UC mechanisms and explain well the observed linear increase of the UC red-to-green intensity ratio with the increment of Ce(3+) ion concentrations.
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