Emission dynamics of the F-4(3/2) level of Nd3+ in YAG at low pump intensities

The room-temperature high-resolution luminescence decay investigation of YA G crystals doped with Nd3+ in concentrations up to 1.5 at.% shows that unde r nonselective weak 532-nm pump, which prevents the up conversion, the emis sion dynamics of F-4(3/2) level is influenced by a cross relaxation inside the system of Nd3+ ions, dominated by superexchange (R-0 = 5.43 Angstrom, L = 0.54 Angstrom) for the nearest-neighbor Nd3+ ion pair and by dipolar cou pling (C-DA = 1.85 x 10(-40) cm(6) s(-1)) for all other pairs. These parame ters are in strong contradiction with other recent reports. The energy-tran sfer parameters are verified in the quasiselectively excited decay of the f irst-, second-, and third-order Nd3+ ion pairs by using a proper adaptation of the theory of energy transfer for discrete, equiprobable, and random pl acement of Nd3+ ions in the crystalline lattice. They give also a very good description of the data on quantum efficiency and fractional thermal load for YAG:Nd3+ samples of various concentrations. The absence of the quadrupo lar interaction in the mechanism of transfer is consistent with the restric tions imposed by the selection rules for the transitions involved in cross relaxation.