Blue up-conversion luminescence and energy transfer process in Nd3+-Yb3+-Tm3+ co-doped ZrF4-based glasses

Up-conversion luminescence properties 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 Nd3+, Yb3+, and Tm3+, both Nd3+ and Tm3+ have ground state absorption bands due to the (2H9/2, F5/24) ←I9/24 and F43←3H6 transitions, respectively, which can be directly pumped by 800 nm light. 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 on the excited state and, finally, blue up-conversion emission of Tm3+ is observed through the Tm3+: 1G4→3H6 transition. It was also demonstrated that the energy on the Tm3+: 1G4 level was back-transferred to Nd3+ in the Nd3+ high-concentration region, quenching the up-conversion luminescence.