B. Jacquier

One- and two-photon spectroscopy of Ce3+ ions in LaF3-CeF3 mixed crystals

Absorption, excitation and emission spectra and lifetime measurements in cerium-doped lanthanum fluoride single crystals were obtained using both one- and two-photon spectroscopy techniques. It is shown that two kinds of fluorescent centres are present. In weakly doped systems, a rapid fluorescence around 300 nm dominates, due to Ce3+ ions at normal sites. In heavily doped systems, an additional longer fluorescence appears at higher wavelengths due to Ce3+ ions occupying perturbed sites and acting as traps. In CeF3, the energy migrates among Ce3+ ions and is finally trapped so that only the trap emission is detected at room temperature. Significant energy losses in the fluorescence of Ce3+ at normal sites are explained by up-conversion and ionization processes and by non-radiative surface recombination phenomena for the case of strong absorption. Two-photon excitation spectra in the region of trap absorption confirm the role of traps in emission mechanisms and show narrow lines which could be vibronic structures of various kinds of traps existing in these materials.

Energy transfer in Li6Gd(BO3)3

In the new material Li6Gd(BO3)3 Gd3+ ions belong to parallel chains separated by about 7A for an intrachain distance of about 4A, so that the energy transfer among Gd3+ ions is expected to be mostly one-dimensional. The Gd3+ 6P7/2→8S7/2 fluorescence has been studied from 300K to 1.5K. Above 40K the fast exponential fluorescence decay indicates fast diffusion of the energy among the Gd3+ ions and trapping by impurities. Below 40K the energy transfer takes place predominantly toward perturbed Gd3+ ions and is diffusion-limited. The nonexponential intrinsic fluorescence decay consists in a short-time component corresponding to diffusion and a longtime component coming from thermal back-transfers from,the traps. The cross-over from a fast diffusion regime to a diffusion-limited regime is discussed in relation to the one-dimensional crystal structure.

Dy3+-doped stabilized GeGaS glasses for 1.3 μm optical fiber amplifiers

Abstract Dy 3+ -doped stabilized-GeGaS sulfide glasses are synthesized and characterized. When antimony is added to GeGaS, the glass shows very weak crystallization upon heating as compared to standard compositions. Because of the low phonon energy inherent in sulfide glasses, the 1.3 μm emission of Dy 3+ ions can be observed. This transition is characterized in terms of emission cross-section and quantum efficiency.

Fluoride crystals and high lying excited states of rare earth ions

Abstract We present the advantage of fluoride crystal hosts for the study of high lying localised excited states of rare earth ions. Special attention is devoted to the study of broad band UV emissions for solid state tuneable UV lasers and to the illustration of photoionisation mechanisms involving indium ions.

Infrared to visible conversion in rare-earth-doped planar waveguides

The first observation of optical properties of new rare-earth-doped vitreous fluoride waveguides has been recently reported. These vitreous fluoride films have been deposited by a physical vapour deposition technique on fluoride substrates. Several PZG films and sandwiches deposited on various substrates have been prepared with thickness of a few μm and doped in the guiding layer by various amounts of erbium and other rare-earth ions. High δn/n (10−2) has been achieved as a result of the glass compositions. Infrared as well as green and blue upconversion pumped fluorescences have been recorded under side light injection.

Spontaneous emission into planar multi-dielectric microcavities: Theoretical and experimental analysis of rare earth ion radiations

Abstract Spontaneous emission control for rare earth ions implanted inside planar multidielectric microcavities is investigated theoretically and experimentally. Rigorous classical electrodynamics analyses are presented and compared in order to compute the electromagnetic power provided by sources located inside planar dielectric multilayer structures. Radiation patterns and lifetime measurements are performed in Ta 2 O 5 /SiO 2 microcavities implanted with erbium and praseodymium ions. Although we demonstrate a significant enhancement of the spontaneous emission in a direction normal to the layer (up to 30%), we show that a large amount of the emitted power is carried by the guided modes of the structures.

Second-harmonic generation in He + -implanted gadolinium calcium oxoborate planar waveguides

What is believed to be the first investigation of second-harmonic generation (SHG) in Ca(4)GdO (BO(3))(3) waveguides is reported. A planar waveguide was formed by 2-MeV-helium implantation. We cut the sample to achieve type I noncritical phase matching of an 823-nm fundamental wave for fundamental light propagating along the y axis and polarized along the z crystallophysic axis of the crystal. SHG was achieved with a relatively low pumping power of a cw Ti:sapphire laser. The results indicate that the nonlinearity of the material remains in the guiding region after ion implantation.

A spectroscopic study of BaY2F8: Nd3+

Abstract Absorption and fluorescence measurements at low temperature were used to obtain an energy level scheme for the Stark components of the Nd 3+ manifolds in BaY 2 F 8 up to 40 000 cm -1 . The fluorescence lifetimes of the 4 F 3/2 , 2 P 3/2 , 4 D 3/2 , and 2 F(2) 5/2 levels were also measured between helium and room temperatures.

One- and two-photon spectroscopy of Pr3+-doped YAlO3 crystals

The energy level position of the Pr3+ ion in YAlO3 and dynamics of the 1G4 1D2 and 3P0 excited states have been analysed. The mechanism of orange and infrared light up-conversion into blue 3P0-state emission has been elucidated and has been considered for possible use in a blue-wavelength laser. Two-photon absorption transitions from the 3H4 ground state to the 3P2 manifold were observed and compared in intensity with the excited-state transitions via the intermediate 1G2 manifold.

Electronic exchange interaction effect on the fluorescence properties of terbium magnetic insulators

Abstract The dynamic properties of Tb 3+ fluorescence in the magnetic insulators TbF 3 , TbAlO 3 and TbPO 4 have been investigated above and below the magnetic phase transition. Spectral identification of the transition 5 D 4 → 7 F 6 has been performed and is in agreement with a crystal field description including interionic interactions. A dramatic change of the exciton decays occurs both in TbF 3 and TbAlO 3 below the ferromagnetic ( T C = 3.95 K ) and antiferromagnetic ( T N = 3.8 K ) phase transitions respectively, while it is not observed for the antiferromagnet TbPO 4 ( T N = 2.2 K ) and the non-ordered material terbium ethylsulfate. Throughout the range from 300 to 1.6 K, the experimental fluorescence decays of TbF 3 and ThPO 4 are in agreement with a rate equation model involving fast diffusion energy transfer among intrinsic ions. On the other hand, the fluorescence dynamics of TbAlO 3 follow a fast diffusion process above T N and exhibit a diffusion-limited energy transfer mechanism below T N with a reduction of the diffusion coefficient by four orders of magnitude. This interpretation agrees with the observation of new optical lines in the excitation spectra which are attributed to direct excitation of traps. We propose to explain all these fluorescence properties in terms of the short range Tb 3+ —Tb 3+ interactions and the nature of the ground state wavefunction of the rare-earth ion in the ordered state.