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BGO single crystals doped with Er3+, Tm3+ and Ho3+ rare-earth ions were prepared in the form of rod-type crystal fibers via the micro-pulling down technique to perform an extensive investigation of their visible, near- and mid-infrared luminescence properties and to really decide on their interest as solid-state laser media in the various spectral domains. Revisiting and completing the absorption spectra already available in the literature led to the derivation of more reliable "effective" radiative lifetimes and branching ratios. Registration of the fluorescence decays of the most important emitting levels versus dopant concentrations led for the first time to an unambiguous determination of "intrinsic" emission lifetimes – corresponding to negligible contributions from inter-ionic energy-transfers - and non-radiative multiphonon relaxation rates. Such data also allowed for the determination of the dominant phonon energy which comes into play in the electron-phonon coupling responsible for these multiphonon relaxation processes and for its lattice vibration origin, i.e. a high phonon energy of the order of 820 cm−1 corresponding to the coupling between bending vibrations of (GeO 4)4- tetrahedra and vibrations corresponding to motions of these (GeO 4)4- tetrahedra against the Bi3+ ions for which the rare-earth dopant ions substitute. Using the above data and different methods for the calibration of the registered emission spectra in cross section unit and for the derivation of gain cross section curves finally show that mid-infrared emissions of Er:BGO, Tm:BGO and Ho:BGO around 1.55 μm, 1.9 μm and 2 μm, respectively, occur with comparable gain cross sections as in the most important reference mid-infrared laser materials, although over slightly shifted thus complementary spectral domains. It is shown that potentialities also exist with Tm:BGO in the blue, deep-red and near-infrared spectral domains around 470 nm, 800 nm and 1.45 μm, by pumping the crystals with conventional pump sources and using some suitable co-dopants to avoid detrimental self-terminating processes. • Bi 4 Ge 3 O 12 rod-type crystal fibers doped with Er3+, Tm3+ and Ho3+ ions are successfully grown by using the micro-pulling down technique. • An extensive spectroscopic investigation is performed from the near-UV to the mid-infrared. • Effective radiative and intrinsic emission lifetimes are unambiguously determined for all the important emitting levels. • The origin and the energy of the phonons responsible for the non-radiative multiphonon relaxation of the emitting levels are clearly identified. • Emission and gain cross section spectra show the interest of Er3+, Tm3+ and Ho3+ doped BGO crystals for the high power mid-infrared laser application. [ABSTRACT FROM AUTHOR]

The luminescence properties of 0.5%Pr-doped BGO crystals grown by using the micro-pulling down technique were carefully investigated. Room temperature absorption spectra were registered and analyzed within the framework of the Judd-Ofelt formalism and the best fit to the data is obtained by using a modified treatment allowing for the admixture of intensity enabling wave-functions. The results indicate 3P 0 and 1D 2 radiative lifetimes of about 5.7 μs and 79 μs, in perfect agreement with the time-constants derived from the measured fluorescence decays at room and liquid-nitrogen temperatures. Registration of time-resolved emission and excitation spectra and calibration of the 3P 0 emission spectrum in cross section unit clearly indicate that Pr-doped BGO could be the first isotropic crystalline material leading to efficient diode-pumped laser operation at room temperature with laser performances, at least in the deep-red spectral region, comparable to that found with the most important anisotropic Pr-doped fluoride and oxide crystals. • Pr:Bi 4 Ge 3 O 12 crystal fibers are successfully grown by micro-pulling down. • Absorption spectra are analyzed by using the Judd-Ofelt formalism. • Emission, excitation spectra are registered from the near-UV to the deep-Red. • It is found a 3P0 emission lifetime of 5.7 μs for a quantum yield close to 1. • Record emission cross-sections are obtained in the red and deep-red. [ABSTRACT FROM AUTHOR]