Site-selective laser spectroscopy of BaF2:Eu3+

The selective laser excitation of the flourescence of Eu³⁺ ions is used to investigate the defect sites in BaF₂:Eu³⁺ for Eu³⁺ concentrations ranging from 0.03 to 2.43 mol%. We identified the fluorescence lines arising from the (Eu³⁺, F^-_i) dipole of C_3v symmetry and established its energy level diagram. The compensating ion is an interstitial F^-_i ion located in the next-nearest-neighbour site, with respect to the Eu³⁺ ion. This (Eu³⁺, F^-_i) dipole dominates in BaF₂. Fluorescence lines assignable to next-nearest-neighbour pairs of (Eu³⁺, F^-_i) dipoles have been found above 0.1 mol% dopant concentration.     

Formation of new Tm3+ tetragonal symmetry optical centers in CaF2 hot-formed laser ceramics

By means of time-resolved site-selective spectroscopy the formation of new Tm³⁺ optical centers with modified local environment and presumably tetragonal local symmetry in CaF₂ hot-formed laser quality ceramics is observed. The spectroscopic properties of these new Tm³⁺ optical centers are investigated and shown to differ strongly from that for regular tetragonal optical centers.

     

EPR of trivalent chromium centers with monoclinic symmetry in SrF2 crystals

Cr³⁺ centers with monoclinic symmetry in SrF₂:Cr crystals are studied by EPR. Based on an analysis of the EPR data and a study of the conditions under which the observed samples were formed, a model is proposed which explains the low symmetry of the magnetic properties in terms of the simultaneous effect on the impurity ion state of interactions with the interstitial F⁻ ion and with normal vibrations of the crystal lattice in a trigonal symmetry. Fiz. Tverd. Tela (St. Petersburg) 39, 302–305 (February 1997)     

Role of monovalent alkali ions in the Yb3+ centers of CaF2 laser crystals

Yb³⁺ and M⁺ monovalent alkali ions (M⁺ = Li⁺, Na⁺, K⁺)-co-doped CaF₂ cubic laser crystals were grown by the micro-pulling-down method (μ-PD) under CF₄ atmosphere. Structural and spectroscopic characterizations of Yb³⁺ in substitution of Ca²⁺ (absorption, emission and decay curves) were carried out to study the effect of M⁺ ions as charge compensators.     

Study of Nd2+ absorption in x-irradiated CaF2, SrF2, BaF2 crystals

The absorption spectra of x-irradiated alkaline-earth fluoride (CaF₂, SrF₂, BaF₂) crystals doped with Nd³⁺ ions have been investigated. X-irradiation results in creating the absorption bands of inter-configuration 4fⁿ–4fⁿ⁻¹–5 d¹ transitions of Nd²⁺. The charge reduction of the neodymium by irradiation is not temperature-stable and the ions reoxidation (Nd²⁺ → Nd³⁺) occurs under heating to 570 K in CaF₂, 520 K in SrF₂ and 470 K in BaF₂.     

SrF2:Nd3+ laser fluoride ceramics

SrF(2):Nd(3+) fluoride ceramics of high optical quality was prepared and its spectroscopic and laser properties investigated. Oscillations of different optical centers depending on the excitation wavelength were obtained with a slope efficiency of up to 19%.     

Hyperfine patterns of infrared absorption lines of Ho3+ C4v centres in CaF2

Hyperfine structure is observed on several infrared transitions to the ⁵I₇ and ⁵I₆ multiplets of the Ho³⁺ C_4v centre in CaF₂. Particularly complex and detailed hyperfine structures are observed for transitions to the Y₃ level of the ⁵I₇ multiplet, which include the appearance of ΔI_z ≠ 0 transitions. The hyperfine lines of this level are satisfactorily accounted for by strong mixing of close-lying levels of this multiplet by the perpendicular hyperfine interaction, which leads to relaxation of the ΔI_z = 0 selection rule and a redistribution of the hyperfine intensities over many transitions. An excellent correspondence is found between the measured and simulated spectra.     

Optical echo spectroscopy and phase relaxation of Nd3+ ions in CaF2 crystals

Accumulated photon echoes have been used to investigate the mechanisms of optical dephasing in CaF₂ crystals activated by Nd³⁺ ions. Tunable picosecond laser radiation, which permits the selective excitation of various Nd³⁺ optical centers in the ⁴ I _9/2→⁴ G _5/2, ² G _7/2 transition, is used. The optical phase relaxation times measured at temperatures from 9 to 50 K permit determination of the homogeneous widths of the transitions between the low-lying ⁴ I _9/2 Stark level and three excited ⁴ G _5/2, ² G _7/2 levels, and calculation of the constants of the inter-Stark relaxation transitions in the ground and excited multiplets for the rhombic N and M Nd³⁺ centers in CaF₂ crystals. An analysis of the temperature dependence of the homogeneous linewidth of the transitions between low-lying Stark levels of the ground and excited states shows that the mechanism of optical dephasing in the crystals investigated is described well by direct relaxation processes with resonant inter-Stark absorption of one phonon in the ground and excited states. At T=9 K, the homogeneous linewidth Γ_h in CaF₂ crystals is almost an order of magnitude smaller than Γ_h in disordered CaF₂-YF₃ crystals. This difference can be attributed to the significantly greater spectral phonon density of states in disordered crystals. Zh. éksp. Teor. Fiz. 113, 278–290 (January 1998)     

Infrared transitions of C2D6 from v 4 to the interacting system v 4+ v 6, v 4+ v8, v 3+ 2v 4: rotational analysis,and torsional splitting in the v 3+ 2v 4 and v 3+ v 4 states

The hot infrared transitions of C₂D₆ from the υ₄(A_1u ) to the υ₄ + υ₆(A_2g ) and υ₄ + υ₈(E _g ) vibrational states, observed from 960 to 1180 cm^?1, have been rotationally analysed on a high-resolution Fourier transform spectrum (full width at half-maximum about 0·0030 cm^?1). The vibration-rotation interactions affecting the upper vibrational states are very similar to those of the corresponding cold system. A strong x,y Coriolis interaction between υ₄ + υ₆ and υ₄ + υ₈, with K-level crossing, generates large displacements of the rotational components of both vibrational states, tuning them to additional local resonances in several spectral regions. Thus l resonances with Δl = ±2, Δk = ±1 occur within υ₄ + υ₈. A x,y Coriolis-type resonance between υ₄ + υ₈(?l,K ? 1) and υ₃ + 2υ₄(K) occurs at K = 11,12,13, and a further coupling of υ₄ + υ₈(+l,K + 1) and υ₃ + 2υ₄(K + 3) is most effective at K = 11 and 12. These resonances induce torsional splittings on the perturbed levels of υ₄ + υ₈ and allow us to determine the torsional splittings in the υ₃ + 2υ₄ state. The vibration-rotation constants of υ₄ + υ₆, υ₄ + υ₈ and υ₃ + 2υ₄, several interaction parameters and the torsional splitting of υ₃ + 2υ₄ have been determined by least-squares fit of 1391 observed transition wavenumbers, with an overall standard deviation σ = 0·75 × 10^?3 cm^?1. The vibrational wavenumbers found for the four torsional components of (υ₃ + 2υ₄)? υ₄ are υ(E_3d) = 1040·961 82(809)cm^?1, υ(A_3d) = 1041·218 27(865)cm^?1, υ(E_3s) = 1041·225 23(662)cm^?1 and υ(A_1s) = 1041·407 77(633)cm^?1. These are anomalous for both the order of the torsional components and the magnitudes of their separations. We believe that this is mainly due to the interactions of υ₃ + 2υ₄ with the torsional manifolds with υ₃ = 0 and υ₃ = 2, through the vibration-torsion Hamiltonian term (?V ₆/?q ₃)q ₃cos (6γ)]/2. The further observation of a few doublets of υ₈ and υ₃ + υ₄ at resonance provides information on the torsional splitting of the latter state.     

Selective laser spectroscopy of Mn4+-Mn4+ pair centers in SrTiO3 crystal

Zero-phonon lines of a pair center of Mn⁴⁺ ions are observed in the luminescence and luminescence-excitation spectra of SrTiO₃:Mn crystal. Based on the experimental data, the energy-level structure of the ground state ∣⁴ A _2g ,⁴ A _2g 〉 and excited state ∣⁴ A _2g ,² E _g 〉 of the Mn⁴⁺-Mn⁴⁺ pair center is constructed. It is shown that the exchange interaction in the ground state of the Mn⁴⁺-Mn⁴⁺ pair is antiferromagnetic. Energies of the levels are calculated assuming that the pair is formed by Mn⁴⁺ ions occupying neighboring octahedral positions of Ti⁴⁺ ions along the [110] axis. Experimental values of the exchange integral in the ground state ∣⁴ A _2g ,⁴ A _2g 〉 and energies of spin multiplets in the excited state ∣⁴ A _2g ,² E _g 〉 agree well with calculation of the exchange interaction carried out within the framework of the channel model with the parameters J _ξη = 32 cm^4-1 and J _ζζ = ?45.5 cm^4-1. Experimental data and calculations unambiguously demonstrate that zero-phonon lines in the luminescence and luminescence-excitation spectra have magnetic-dipole nature.