Direct measurement of the rate of nonradiative relaxation and luminescence spectra from the 4G7/2, 4G5/2+2G7/2, and 4F9/2 levels of Nd3+ ions in LaF3, SrF2, and YAlO3 laser crystals

The kinetics of luminescence decay from the ⁴G_7/2, ²G_7/2+⁴G_5/2, and ⁴F_9/2 levels of Nd³⁺ ions in LaF₃, SrF₂, and YAlO₃ crystals was measured by direct nanosecond laser excitation and recording of the luminescence by a statistical single photon counting technique with a time resolution of up to 0.4 nsec. The luminescence spectra from these strongly quenched states of the Nd³⁺ ion were studied. It was found that excited multiplets separated from the next lower multiplet by energy gaps ΔE=1100–1850 cm^–1 mainly decayed by nonradiative processes within 5–110 nsec. The temperature dependences of the lifetimes and of the probabilities of nonradiative transitions from the ⁴G_7/2 level in an La_0.98Nd_0.02F₃ crystal were determined and these indicated that the relaxation was a four- or five-phonon process.