Laser-induced fluorescence-line-narrowing studies of LaCl3:Nd3+: Static and dynamic aspects

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Abstract
We have applied the fluorescence‐line‐narrowing technique in investigating the interaction of trivalent neodymium ions with each other and with the surrounding lanthanum trichloride lattice. A 0.04 cm−1 linewidth dye laser was used to site‐select sets of impurity Nd3+ ions within the 2 to 5 cm−1 spectral profile of the E1(4G7/2, μ=3/2) excited electronic state. High resolution detection monitored the E1 → Y3(4I11/2, μ=5/2) fluorescence characteristics. Studies were undertaken on two types of crystals. Nonradiative relaxation within the Y(4I11/2) manifold was investigated by measuring homogeneous linewidths in a dilute (0.5 mol %) crystal. The results qualitatively conform to relaxation via a direct one‐phonon process. Crystals with higher Nd3+ concentrations (8% and 15%) were used to probe site variation and energy transfer dynamics. Species with short excited state lifetimes and distinct spectral shifts indicate the presence of distorted sites, most likely clusters of Nd3+ ions. This behavior exemplifies a situation where concentration fluctuation instead of crystalline strain is the major inhomogeneous line broadening mechanism. Dynamic measurements yielded a relatively short‐ranged R−8 dependence on energy transfer rate, indicative of an electric dipole–quadrupole coupling. Phonon‐assisted energy transfer appears to proceed via an Orbach mechanism.