Site-selective and time-resolved fluorescence and excitation spectroscopy of the absorption bands of M and N centers in Nd3+-doped (0.6%) material was carried out at 1.6 and 4.2K by using a pulsed tunable laser. Site-selective excitation and fluorescence spectra (including decay kinetics) were studied for the crystal-field transitions, 4I9/2(1)→4G5/2(1), in absorption and 4F3/2(1)→4I9/2(1) in emission; for various Nd3+ centers. It was shown that the M absorption band, formed mainly by (Nd3+–Fi)2 pair M centers, also contained the spectral lines of other pair modifications. The N band included lines from (Nd3+–Fi)4 quartet N centers and also from higher aggregated Q and R centers and lower aggregated S centers. These centers had different excitation and fluorescence spectra, and different 4F3/2 fluorescence lifetimes. A weak absorption between the M and N bands was attributed to the many so-called D(2a) centers. It was proved that the 4I9/2(1) and 4G5/2(1) Stark levels in these centers were split up into sub-levels. For the pair M and quartet N centers, the total splitting was about 2.5 and 3.5/cm, respectively. Values of 5 and 6/cm were found for the Q and Q′ centers, and a value of 5/cm for the R center.

Fluorescence Line Narrowing and Site-Selective Fluorescence Decay of Nd3+ Centers in CaF2. Y.V.Orlovskii, T.T.Basiev, V.V.Osiko, H.Gross, J.Heber: Journal of Luminescence, 1999, 82[3], 251-8