M.-F. Joubert

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.

Infra-red to visible up-conversion in holmium-doped materials

Infra-red to visible wavelength up-conversion is reported for trivalent holmium ion (Ho3+) doped: YAP, YAG, YLF, SrLaGa3O7 and SrLaGaO4 crystals and ZBLAN glass. The spectra and possible mechanisms of up-conversion are discussed. Changing of the holmium luminescence colour between red and green was observed, after excitation in the 870- to 930-nm band. Wavelength-dependent ground state absorption and excited state absorption resonances were investigated and explained. For discussing the up-conversion pathways, we determined the cross-sections for the excited state absorption and for the non-resonant side-band absorption.

Spectroscopic studies of erbium-doped potassium-lead double chloride crystals KPb2Cl5:Er3+: 1. Optical spectra and relaxation of excited states of the erbium ion in potassium-lead double chloride crystals

Optical spectra, intensities of radiative and nonradiative transitions, and luminescence kinetics in erbium-doped potassium-lead double chloride crystals KPb2Cl5:Er3+s(KPC:Er3+) were investigated. The crystals were grown by the Bridgman-Stockbarger method. Their absorption and luminescence spectra were studied experimentally. The crystal-matrix absorption edge was determined at 80 and 300 K. Intensity parameters, radiative transition probabilities, branching ratios, and nonradiative relaxation rates were estimated by the Judd-Ofelt method. The luminescence kinetics from the emitting levels 4G11/2, 2G9/2, 4S3/2, and 4F9/2 upon selective excitation was studied.

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.

Spectral and dynamic study of the broad band UV 4f25d→4f3 emission in Nd-doped double sodium yttrium fluoride crystals and comparison with Nd:LiYF4

Abstract VUV and UV spectroscopy of 4f 2 5d excited configuration of Nd 3+ ions has been investigated in the double sodium yttrium fluoride crystal Na 0.4 Y 0.6 F 2.2 . The spectral and dynamic properties of Nd 3+ in this disordered structure are compared to those observed for Nd 3+ :LiYF 4 .

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.

Room temperature blue upconverted luminescence via photon avalanche pumping in Cs2NaGdCl6:Tm3+

Experimental results are presented to show that the intense, blue upconverted luminescence observed from Cs2NaGdCl6 doped with 6,10 and 15 at.% Tm3+, when excited by a cw laser near 650 nm at room temperature, is due to a photon avalanche process. A slow rise of the upconverted blue-emission intensity, over several seconds, takes place near the threshold power level. Emission is not only observed from the1G4 term manifold, but also from1D2. The well-resolved upconversion excitation spectrum indicates clearly that excited-state absorption to1G4 takes place from the3F4 multiplet term of Tm3+.

Avalanche upconversion in Tm3+-doped BIGaZYTZr glass

Abstract Intense blue fluorescence is observed in a Tm3+-doped BIGaZYTZr fluoride glass after single wavelength red or infrared CW pumping. Dynamics and power dependences of both1G4 and1D2 fluorescences under 648.7 nm excitation reveal a photon avalanche mechanism in the 3 mol% doped sample. Selective pulsed excitation indicate an almost purely radiative relaxation at low concentration in agreement with Judd-Ofelt calculations. At higher concentration, cross-relaxation energy transfer and excited state absorption mechanism compete to feed the1G4 and1D2 levels. The concentration, temperature and time dependences of these fluorescences are investigated.

Blue up-conversion emission in Yb3+ sensitized YAG:Pr3+

One-color infra-red laser pumping of YAG:Pr3+ + Yb3+ crystals results in a strong up-converted blue fluorescence from the excited3P0 multiplet. Up-conversion fluorescence intensity increases as the square of incident pump power indicating two-ion process. The first step is the efficient nonradiative energy transfer from2F5/2 level of Yb3+ to the1G4 level of Pr3+. The second step is an excited-state absorption (ESA) from the1G4 multiplet. The resonance between the first-step pumping process and the second-step ESA is strongly temperature dependent.