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Up-conversion processes are studied in (Yb 3+ , Tb 3+ ) co-doped fluorophosphate glasses. These glasses contain a large concentration of terbium fluoride, up to 36 mol%, and still luminesc. Samples are excited at 980 nm, within the Yb 3+ absorption band. For `low' Yb 3+ concentrations, i.e., below 16 mol%, the typical green luminescence of terbium is observed. With increasing Yb 3+ concentration, the green luminescence vanishes and a blue emission appears. Both emissions are due to a cooperative effect between two Yb 3+ ions.

The optical absorption and magnetic circular dichroism (MCD) spectra of 1% Nd 3+ doped fluorozirconate (ZBLAN) glass are reported. The glass composition is 53 mol% ZrF 4 , 20 mol% BaF 2 , 20 mol% NaF, 3 mol% AlF 3 , 3 mol% LaF 3 and 1 mol% NdF 3 . An analysis of the intensity of the absorption spectrum is done in the framework of the Judd-Ofelt theory. The Judd-Ofelt intensity parameters are Ω 2 = 1.76(±0.22) × 10 −20 cm 2 , Ω 4 = 3.08(±0.30) × 10 −20 cm 2 and Ω 6 = 3.67(± 0.32) × 10 −20 cm 2 . This parameter set is compared with those for Nd 3+ in other vitreous matrices. The small value of the Ω 2 parameter can be related to the high ionicity (= low covalency) between the neodymium cation and fluoride anions and/or to a relatively high symmetry of the local surrounding of the neodymium ion. Correlation between the intensity parameters and the size of the modifier is not possible because, in fluoride glasses, the lanthanide ions are intermediate elements and can be both in and out the network positions. It is emphasized that one should not correlate too much physical properties to only three phenomenological parameters. The spectral features of the MCD spectra are described qualitatively. The MCD signals show a strong temperature dependence. A negative A -term is found for the 2 P 1 2 → 4 I 9 2 transition at room temperature. The ratios C 0 D of the Faraday parameter C 0 to the dipole strength D are reported.

Novel fluorophosphate glasses containing a heavy concentration of Tb 3+ ions are studied in terms of optical absorption and emission, and decaytimes. From the 5 D 4 emitting level, an intense green luminescence is observed. The decay is single-exponential whatever the terbium concentration which can be as large as 36 mol%. At high concentrations, a fast diffusion process is responsible for the energy migration from that level. For 5 D 3 , on the other hand, emissions are strongly concentration-dependent, and the decays are well accounted for by the Inokuti-Hirayama model.

A resonant technique, based on the sinusoidal modulation of the pump beam intensity, is demonstrated in the case of the precise measurement of the lifetime of the 4 I 13 2 level of erbium ions in fluorophosphate hosts. This intensity modulation is obtained via a rotation of the polarization of the pump beam. The large signal-to-noise ratio enables the use of low pump power and apparent lifetime shortenings due to ion-ion energy transfer processes and to amplification of spontaneous emission are circumvented. A parallel ith decay times deduced from usual fluorescence decay measurements is performed. Extension of the method to the spectroscopy of other rare-earth ions is discussed.

Optical absorption and magnetic circular dichroism (MCD) spectra of 1% Pr3+ doped ZBLAN fluorozirconate glass have been recorded at several temperatures between 4.2 K and room-temperature. The dipole strengths of the 4f–4f transitions are parametrized in terms of three phenomenological Judd–Ofelt intensity parameters Ωλ (λ=2, 4 and 6). The method of moments was used to extract the Faraday parameters from the MCD spectra. While the room-temperature MCD spectra are dominated by A-terms (which have the shape of the first derivative of an absorption curve), C-terms become more important at lower temperature. The temperature dependence of the 3P0←3H4 transition is a typical example. The temperature dependent change of the MCD spectrum can be explained by the differential thermal population of the Zeeman levels from which absorption of left and right circularly polarized light takes place.