Quantum cutting in GdxY1−xLiF4: Nd—dynamics and mechanisms

Nd3+-sensitized quantum splitting for the Gd3+–Nd3+ couple is studied in mixed GdxY1−xLiF4: Nd phosphors as a function of the Gd3+ concentration. Quantum splitting is observed for all samples studied which include the concentration range image. After excitation of the 4f25d state of Nd3+, rapid energy transfer occurs to Gd3+ as evidenced by the decrease of 4f25d emission with increasing x. The quantum splitting involves a cross relaxation in which the 6G state of Gd3+ undergoes a downward transition to its lower lying 4f7 levels with the simultaneous transition of Nd3+ from its ground state to an excited state in the 4f3 configuration that is resonant with the Gd3+ downward transition. The dynamics are strongly affected by x. For image, the buildup of the 6P emission of Gd3+ 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 Gd3+. The slower time scale is similar to that of isolated Gd3+ 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.