Selective enhancement of green upconversion emissions of Er3+:Yb3Al5O12 nanocrystals by high excited state energy transfer with Yb3+–Mn2+ dimer sensitizing

An innovative upconversion (UC) emissions route of Er3+ by Yb3+–Mn2+ dimer sensitizing in Er3+–Mn2+:Yb3Al5O12 (YbAG) nanocrystals is reported here, which resulted in the selective enhancement of green UC emission and suppression of red UC emission by a 976 nm laser diode excitation. By codoping of Mn2+, the green UC emission intensity increased about 260 times, while the red UC emission intensity decreased about 20 times than that of Er3+:YbAG nanocrystals. It indicates that the green enhancement and red suppression arise from the high excited state energy transfer with |2F7/2, 4T1g> (Yb3+–Mn2+ dimer) to the 4F7/2 (Er3+), which partly decreases the nonradiative processes happened in the lower levels of Er3+. The proposed sensitizing route here may constitute a promising step to realize high-efficient UC emissions of rare-earth ions doped oxides and significantly extend their scope of applications.