Highly efficient blue up-conversion of Tm3+ in Nd3+–Yb3+–Tm3+ co-doped ZrF4-based fluoride glass

Up-conversion luminescence and energy-transfer processes in Nd3+, Yb3+ and Tm3+ co-doped ZrF4-based fluoride glasses have been studied under 800 nm light excitation. Blue up-converted emission around 478 nm which can be assigned to the Tm3+:1G4→3H6 transition, was strongly observed. Up-conversion luminescence intensity exhibited an YbF3-concentration dependence. Among the Nd3+, Yb3+ and Tm3+, Nd3+ and Tm3+ have ground state absorption bands due to the (2H9/2,4F5/2)←4I9/2 and 3F4←3H6 transitions, respectively, which can be directly pumped by 800 nm radiation. However, no emissions were observed in Tm3+ singly-doped and Tm3+–Yb3+ doubly-doped glasses under 800 nm excitation. Therefore, a possible up-conversion mechanism may be proposed as follows: energy-transfer firstly occurs from Nd3+ to Yb3+ when Nd3+ is excited by 800 nm light, then the energy is transferred from Yb3+ to Tm3+ which is in the excited state and, finally, blue up-conversion emission of Tm3+ is observed through the Tm3+:1G4→3H6 transition.