Unusual power-dependent and time-dependent upconversion luminescence in nanocrystals Y2O3: Ho3+/Yb3+

The unusual power-dependent and time-dependent upconversion luminescence (UCL) in nanocrystals Y2O3: Ho3+/Yb3+ was reported under 978-nm excitation. It was observed that the UCL intensity increased as the excitation power increased under lower excitation density, but decreased in the case of higher excitation density. At lower excitation density, the intensity solely increased with exposure time. As the excitation density reached a certain value, a maximum of intensity appeared as a function of time. Under higher power density, the intensity solely decreased with time. Similar phenomenon was also observed in Er3+-doped and Tm3+-doped samples. The origin of unusual power- and time-dependent UCL was discussed.