Quantum cutting in Gd xY 1−xLiF 4: Nd—dynamics and mechanisms

Abstract

Nd 3+-sensitized quantum splitting for the Gd 3+–Nd 3+ couple is studied in mixed Gd x Y 1− x LiF 4: Nd phosphors as a function of the Gd 3+ concentration. Quantum splitting is observed for all samples studied which include the concentration range 0.1 < x < 1 . After excitation of the 4f 25d state of Nd 3+, rapid energy transfer occurs to Gd 3+ as evidenced by the decrease of 4f 25d emission with increasing x. The quantum splitting involves a cross relaxation in which the 6G state of Gd 3+ undergoes a downward transition to its lower lying 4f 7 levels with the simultaneous transition of Nd 3+ from its ground state to an excited state in the 4f 3 configuration that is resonant with the Gd 3+ downward transition. The dynamics are strongly affected by x. For x < 0.2 5 , the buildup of the 6P emission of Gd 3+ has two distinct components with very different time scales, microseconds and milliseconds. The rate of the fast component increases with a reduction in x. This points to the role of energy migration among Gd 3+. The slower time scale is similar to that of isolated Gd 3+ ions. The existence of these two very distinct temporal regimes points to the importance of exchange, which is a very short range interaction, in the quantum cutting process.