Energy transfer process and Tb3+ up-conversion luminescence in Nd3+-Yb3+-Tb3+ co-doped fluorozirconate glasses

Up-conversion properties and energy transfer processes in Nd3+, Yb3+ and Tb3+ co-doped ZrF4-based fluoride glasses have been studied under 800 nm light excitation. Blue (490 nm), green (545 nm), yellow (580 nm) and red (624 nm) up-converted emissions which can be assigned to the Tb3+ : D-5(4) --> F-7(J) (J = 6, 5, 4 and 3) transitions, respectively, were strongly observed. Among the Nd3+, Yb3+ and Tb3+ ions, only Nd3+ has a ground state absorption due to the (H-2(9/2), F-4(5/2)) <-- I-4(9/2) transitions which can be directly pumped by 800 nm radiation. Therefore, a possible up-conversion mechanism is proposed as follows: At first, Nd3+ is excited by 800 nm light, followed by the energy transfer from Nd3+ to Yb3+, and finally "co-operative energy transfer" occurs between two excited state Yb3+ and one ground state Tb3+. It was also demonstrated that the energy back-transfer from Tb3+ to Nd3+, causing quenching of up-conversion luminescence. (C) 2000 Elsevier Science B.V. All rights reserved.