[en] Subjects covered in this book include echocardiography, nuclear cardiology, magnetic resonance imaging, computerized tomography, digital angiography and a final chapter on older but still clinically useful noninvasive techniques

[en] Persistent spectral holes in the inhomogeneously broadened 4f¹-4f⁰5d¹ zero-phonon transitions in LuPO₄:Ce³⁺ and YPO₄:Ce³⁺ crystals were burned at T=2 K. The holes observed in absorption were deep (up to 50%) and could be observed at least minutes after they were burned. The burning process was very efficient and is due to a single photon process. The observed spectral holes are burned in a photochemical process of photoionization of Ce³⁺ ions involving electron tunneling from Ce³⁺ centers to traps

[en] The signs of the energy dispersion of one-dimensional excitons in Tb(OH)₃ are determined from the time-resolved spectrum of the exciton band-to-band luminescence by monitoring the time evolution of the different wavevector states after excitation of the k approximately 0 excitons with a pulsed tuneable dye laser. (author)

[en] Optical dephasing of rare-earth ions doped in LaF₃ nanocrystals embedded in the glass ceramics is studied by the two-pulse photon echo. It is found that the dephasing time, T₂, is 30-50 ns for ³H₄-³P₀ transition of Pr³⁺-doped samples that has a nanoparticle size of 30-40 nm. A quasilinear temperature dependence is observed and a zero-temperature residual line width is also obtained as seen by spectral hole burning. Possible mechanisms that dominate the dephasing process and that contribute to the spectral diffusion (slower process) are discussed by comparing the echo results with those of the spectral hole burning

[en] We report optical studies of the new material - Cr³⁺-doped lithium-germanate glass, containing Li₂Ge₇O₁₅ (LGO) nanocrystalline particles. While only broadband ⁴T₂-⁴A₂ fluorescence from the low-field octahedral Cr³⁺ sites was observed from Cr³⁺ ions in the glass, in LGO nanocrystals high-field Cr³⁺ centers emit ²E-⁴A₂ (R-lines) fluorescence. The process of crystallization in the course of isothermal annealing of glasses was monitored spectroscopically and the nucleation of LGO crystallites was observed starting from the smallest clusters. Using the ²E-⁴A₂ fluorescence spectra it is possible to detect the ferroelectric phase transition in LGO:Cr³⁺ nanocrystals, whose critical temperature was found to be similar to that of the bulk crystals. Long-lived spectral holes were burned in the inhomogeneously broadened R-lines of Cr³⁺ in LGO nanocrystals at low temperatures. The linear temperature dependence of hole widths shows that the homogeneous broadening of ⁴A₂-²E transitions of Cr³⁺ in nanocrystals is due to interaction of Cr³⁺ electronic levels with the two-level systems (TLS) of the surrounding glass. The range of the Cr³⁺-TLS elastic dipole-dipole interaction is estimated

[en] A two-step photoconductivity measurement in Gd₂O₃:Er³⁺ is used to determine the location of the f¹¹ energy levels of Er³⁺ with respect to the host bands of Gd₂O₃ . Photoconductivity (PC) experiments were performed with both a tunable UV source and with 488 nm Ar⁺ excitation, as well as in the presence of both light sources. Using only the UV source, PC features with onsets at 240 and 340 nm are identified as direct band gap excitation and two-step excitation involving excited state absorption on Er³⁺, respectively; the latter is confirmed by its quadratic dependence on intensity. Under simultaneous Ar⁺ excitation, which enhances the population of the metastable ⁴S_3/2 Er³⁺ excited state population, the PC feature with a 340 nm onset increases dramatically and its magnitude depends linearly on both UV and Ar⁺ laser intensity, supporting its interpretation as resulting from excited state absorption form the ⁴S_3/2 metastable Er³⁺ excited state.The 340 nm onset of the signal allows one to place the ⁴I_15/2 ground state at 0.7±0.2 eV below the top of the valence band. The lowest 4f¹⁰5d level then lies close to the bottom of the conduction band and its overlap with the conduction band is thought to enhance the second step in the photoionization process

[en] Red-to-blue up-converted emission has been studied for Pr³⁺-doped fluoride nanocrystals-based oxyfluoride glass ceramics. Emission by the ³P₀-³H₄ transition has been observed upon excitation of the ¹D₂ manifold. The concentration, wavelength and flux dependence of the up-conversion have been investigated at different temperatures from 1.5 K at high spectral resolution. Excitation spectra indicate that the most efficient excitation is at 591.6 nm, which corresponds to the transition of ¹D₂ (II), the second-lowest level of the ¹D₂ manifold. The intensity of the blue emission shows a quadratic dependence on the incident flux. The dynamical processes of this up-conversion have also been examined, suggesting that the energy-transfer process is responsible for the up-converted emission. The different spectroscopic features between nanocrystals and bulk crystals have been characterized, indicating that the local temperature in the nanocrystals is higher than that in bulk crystals due to the lower thermal conductivity of the glass matrix

[en] Transient and persistent spectral hole burning (TSHB and PSHB) experiments were performed on Eu³⁺ ions in sol-gel SiO₂ glasses with aluminum co-doping. Differences in the hole burning behavior were observed among samples made from two organosilicate precursors that were annealed to a series of final temperatures. All glasses exhibited persistent spectral holes when annealed to 800 deg. C but, as the annealing temperature was raised to 1000 deg. C, an increasing number of Eu³⁺ ions exhibited TSHB with a corresponding decrease in the number of ions showing PSHB behavior. The transient hole burning behavior is similar in nature to that observed for Eu³⁺-doped silicate melt glass

[en] The emissive properties of fluorescent and laser materials demonstrate a marked dependence on the equilibrium phonon population, in the form of a temperature dependence of the optical linewidths (dephasing time). Under conditions of pulsed excitation a nonequilibrium phonon population an be generated which can effect not only the spectral distribution of the optical emission but also the lifetime of the transition. In this work the effect of dephasing of the ³H₄-³P₄ transition in LaF₃:Pr³⁺ by a non-equilibrium phonon population is investigated. A nonequilibrium phonon population is generated using far infrared (FIR) radiation to pump a low lying electronic state which can then relax by the emission of resonant phonons. The effect of nonequilibrium phonon populations on the dephasing time in this case the nonequilibrium phonon were generated using resonant optical pumping

[en] The pressure dependence of the emission of the 4f¹5d¹ state of Pr³⁺ is reported. Excitation of the 4f¹5d¹ state of Pr³⁺ is accomplished using excited state absorption from the ³P₀ state to populate the 4f¹5d¹ state of Pr³⁺ from which emission is measured as a function of pressure. The emission, which occurs at 320 nm at ambient pressure, is found to shift to lower energy, nearly linearly at a rate of -14.1 cm^-1/kbar. This compares with -12.5 cm^-1/kbar for Ce³⁺ in YAG. The pressure dependence of the 4f¹5d¹ →4f² transitions are explained using a standard crystal field approach and a configurational coordinate model to describe the effects of pressure on the electronic energy of the 4f¹5d¹ state and the electron-lattice coupling. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)