title: Laser power density dependent energy transfer between Tm3+and Tb3+: tunable upconversion emissions in NaYF4:Tm3+,Tb3+,Yb3+microcrystals.
abstract: Energy transfer between Tm3+and Tb3+dependent on the power density of pump laser was investigated in NaYF4: Tb3+,Tm3+,Yb3+microcrystals. Under the excitation of a 976-nm near-infrared laser at various power densities, Tb3+-Tm3+-Yb3+doped samples exhibited intense visible emissions with tunable color between green and blue. The ratio of blue and green emission were determined by energy transfer between Tm3+and Tb3+. When the power density of pump laser was low, the energy transfer process from Tm3+(3F4) to Tb3+(7F0) occurred efficiently. Upconversion processes in Tm3+were inhibited, only visible emissions from Tb3+with green color were observed. When the power density increased, energy transfer from the3F4(Tm3+) to7F0level (Tb3+) was restrained and population on high energy levels of Tm3+was increased. Contribution of upconversion emissions from Tm3+gradually became dominant. The emission color was tuned from green to blue with increasing the power density. Energy transfer processes between low-lying levels of activators, such as Tm3+will greatly reduce the population on certain levels for further high-order upconversion processes. The Tb3+-Tm3+-Yb3+doped phosphors are promising materials for detecting the condition of power density of the invisible near-infrared laser.
authors.forename: Xiaojie
authors.initials: X
authors.lastname: Xue
authors.forename: Makhin
authors.initials: M
authors.lastname: Thitsa
authors.forename: Tonglei
authors.initials: T
authors.lastname: Cheng
authors.forename: Weiqing
authors.initials: W
authors.lastname: Gao
authors.forename: Dinghuan
authors.initials: D
authors.lastname: Deng
authors.forename: Takenobu
authors.initials: T
authors.lastname: Suzuki
authors.forename: Yasutake
authors.initials: Y
authors.lastname: Ohishi