Enhancement of upconversion luminescence in Tm3+/Er3+/Yb3+-codoped glass ceramic containing LiYF4 nanocrystals

A transparent Er3+-Tm3+-Yb3+ tri-doped oxyfluoride glass ceramics containing LiYF4 nanocrystals were prepared. Under 980 nm laser diode (LD) pumping, intensive red, green and blue upconversion (UC) was obtained. The blue, green, and red UC radiations correspond to the transitions 1G4→3H6 of Tm3+, 2H11/2/4S3/2→4I15/2, and 4F9/2→4I15/2 of Er3+ ions, respectively. This is similar to that in Tm3+-Yb3+ and/or Er3+-Yb3+ co-doped glass ceramics. However, the blue UC radiations of the Er3+-Yb3+ co-doped glass ceramics is two-photon process due to cooperative energy transfer. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses.