Direct evidence of reversible energy transfer between Er3+ and Tm3+ ions in upconversion microcrystals

Lanthanide doped NaYF4 microcrystals were synthesized via a facile hydrothermal method. Multicolor upconversion luminescence was observed in NaYF4 microcrystals doped with Yb3+/Er3+, Yb3+/Tm3+, and Yb3+/Er3+/Tm3+ under the excitation of 980 nm infrared light. Importantly, the excitation power density dependence of upconversion emission intensity indicated clearly the energy transfer from Tm3+ to Er3+ ions under the excitation of low power density (5102−9×102 W/cm2). Meanwhile, the inverse energy transfer from Er3+ to Tm3+ ions under the excitation of relatively higher power density (4.1×104−4.9×104 W/cm2) was also revealed. This was a direct evidence for reversible energy transfer between Er3+ and Tm3+ ions. Under the excitation of high power density (4.1×104−4.9×104 W/cm2), dark sensitizers were also motivated so that the bottleneck effect of high concentration Yb3+ ion doping was broken. This was the main reason for realizing high upconversion efficiency of the samples with heavy doping of Yb3+ ion.

The bottleneck effect of high concentration Yb3+ doping was broken under the excitation of relatively higher power density. More interesting, the reversible energy transfer between Er3+ and Tm3+ was directly observed under the excitation of low and high power densityFigure optionsDownload as PowerPoint slide