Polarization of emission spectra from Ti3+-doped oxide crystals

The Ti³⁺ ion in YAlO₃ (YAP), Y₃Al₅O₁₂ (YAG), and Al₂O₃ crystals occupies distorted octahedral sites relative to the nearest neighbour ligand ions. Such distortions are of even-parity in YAG where the zero-phonon lines in emission occur via magnetic dipole transitions. In contrast, the zero-phonon transitions occur by electric dipole processes in Ti³⁺:YAP and Ti³⁺:Al₂O₃ where there are odd-parity distortions from octahedral symmetry. This paper reports measurements of the zero-phonon lines of Ti³⁺ ions in YAP, YAG, and Al₂O₃ at 10 K. The zero-phonon lines of Ti³⁺:YAP are strongly polarized perpendicular to the tetragonal axis and those of Ti³⁺:Al₂O₃ parallel to the trigonal axis. The experimental results are shown to be in accord with a molecular orbital model of the radiative transition according to which the transition intensities derive from odd-parity ligand wavefunctions induced into even-parity ground and excited Ti³⁺ wavefunctions by odd-parity crystal distortions.     

Temperature dependence of the lifetime of Cr3+ luminescence in garnet crystals

The coexistence of sharp R-lines from the ² E state and the broad band from the ⁴ T ₂ state in the photoluminescence spectra of Cr³⁺:Gd₃Sc₂Ga₃O₁₂ (GSGG) and Cr³⁺:Y₃Ga₅O₁₂ (YGG) is observed at low temperature (10K). The decay lifetimes of the broad emission bands of Cr³⁺ in GSGG and YGG are very close to those of the R-lines being, respectively, 0.23 ms and 2.5 ms. These results are explained in terms of the extent of the mixing of the ⁴ T ₂ vibronic wavefunction with that of the ² E lowest excited state by tunnelling.     

Temperature dependence of the lifetime of Cr3+ luminescence in garnet crystals I

The lifetimes of the R-lines from the ² E level and the broad bands from the ⁴ T ₂ level of Cr³⁺ ions in various garnet crystals vary with the energy separation between the ² E and ⁴ T ₂ levels, which change systematically with the composition of host crystal. The trend of the Cr³⁺ lifetimes, as well as their temperature dependences in garnet crystals, is explained by zero-point vibration and phonon-assisted tunnelling between the ² E and ⁴ T ₂ states of Cr³⁺ ion.     

Luminescence from Ti2+ ions in LiF crystals

Luminescence of Ti²⁺: LiF crystals in the wavelength range 650–900 nm excited using laser radiation is reported. The values of 10Dq and the Racah B parameter obtained from the present results indicate that in LiF the ¹ E, ¹ T ₂, and ³ T ₂ energy levels are almost at the cross-over point in the Tanabe-Sugano diagram. In consequence photoluminescence from all three energy levels to the ground state is observed. At low temperature (T 14 K) the emission is mainly due to sharp emission lines with weak vibronic structure due to the ¹ E, ¹ T ₂³ T ₁ transitions of Ti²⁺ ions. The ³ T ₂³ T ₁ broad-band emission is weak at low temperature, becoming stronger at 300 K due to a phonon-assisted tunnelling process, similar to that observed in Cr³⁺: garnets [1]. The excitation spectrum of these lines is a broad peak at 590 nm due to absorption in the ³ T ₁³ T ₂ transition.     

Optical spectroscopy of Cr3+ ions in LiF single crystals

This paper reports on the luminescence spectrum, its excitation-wavelength dependence and decaytime of Cr³⁺:LiF crystals. In contrast to Al₂O₃ and MgO, where the Cr³⁺ luminescence at low temperature is due to the R-line and its vibronic sideband, luminescence from Cr³⁺:LiF is assigned to the broad-band ⁴ T ₂⁴ A ₂ transition. A periodic structure in the vibronic sidebands of this transition occurs with energy separations of ca. 60 meV. The linear polarisation of the vibronic sidebands shows that their radiative transition takes place from the lowest excited level of the ⁴ T ₂ state, i.e. ⁴ B ₁, into the ⁴ A ₂ ground state of Cr³⁺ ions in orthorhombic symmetry sites. The crystal-field parameters calculated from the experimental data, and luminescence decay-time of the two polarized configurations of the ⁴ B ₁(⁴ T ₂)⁴ A ₂ transition are also reported.     

Relaxation dynamics of excited states of Tm3+ in SrGdGa3O7 crystals activated with Tm3+ and Tb3+

3 H₄ and ³F₄ states of Tm in SrGdGa₃O₇ single crystal was evaluated. Tm-Tb energy transfer reduces effectively the lifetime of terminal level in a potential ³H₄-³F₄ laser transition but gives rise to parasitic nonradiative relaxation of the initial ³H₄ level. SrGdGa₃O₇ crystal single doped with thulium possesses combination of properties advantageous for laser oscillations near 1.9 μm, namely high rate of cross relaxation process leading to population buildup on the initial ³F₄ level and relatively high crystal field splitting of the ground ³H₆ level. Received: 25 April 1996/Revised version: 10 October 1996     

Interaction of excited Cr3+ ions in laser crystals

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 56, No. 1, pp. 77–80, January, 1992.     

Oxidation state of Fe and Ti ions implanted in yttria-stabilized zirconia studied by XPS

The oxidation state of Fe and Ti ions implanted in yttria stabilized zirconia (YSZ) was studied by XPS (X-ray photoelectron spectroscopy) in combination with depth profiling using Ar⁺ sputtering. In the as-implanted state of the sample Fe was found to be present as Fe³⁺, Fe²⁺ and as metallic Fe⁰. This is in agreement with earlier conversion electron Mössbauer Spectroscopy measurements. For Ti-implanted YSZ in the as-implanted state the majority of the Ti is present as Ti⁴⁺, Ti³⁺, and Ti²⁺ ions, while a part of the Zr cations is present in the divalent oxidation state (Zr²⁺). After oxidation in air, the Fe and Ti ions are present only in the valence three and four oxidation states, respectively.     

The optical properties of Yb3+ ions in LiTaO3:Nd,Yb crystals

3+ ions excited by energy transfer from Nd³⁺ ions in LiTaO₃:Nd, Yb crystals are presented. The emission band of Yb³⁺ ions is broad, due to the strong phonon-coupling and to the relative large Stark-splitting of the ground ²F_7/2 multiplet. The emission cross-section was evaluated by the reciprocity method, and a value of 0.53×10^-20 cm² was obtained. The gain coefficients derived for the inversion parameters in the range 0.05 to 0.5 indicate positive gain in the 985–1070 nm range. Received: 17 March 1997/Revised version: 10 June 1997     

Radiative decays of doubly excited states of oxygen,carbon, and nitrogen ions

Systematic calculations of the probabilities and energies of radiative transitions in doubly excited 3l3l′, 3l4l′, and 4l4l′ states of oxygen, carbon, and nitrogen ions have been carried out within the Hartree-Fock approximation. The emission spectra are obtained, and analysis of the changes in the spectral characteristics with a change in the charge and the number of additional electrons in the ground state of the initial ion is performed. The data obtained are used to interpret the X-ray spectra of the atmospheres of planets and comets.     

Optical spectra and luminescence dynamics of Pr3+ and Nd3+ in SrLaAlO4 single crystals

Single crystals of SrLaAlO₄: Pr³⁺ and SrLaAlO₄: Nd³⁺ have been grown by the Czochralski method and their optical properties have been studied for different activator concentrations. The absorption and emission spectra of the activators are inhomogeneously broadened because the Sr²⁺ and La³⁺ ions are distributed randomly on the sites ofC ₄ symmetry, however, the symmetry selection rules are still obeyed. Strong self-quenching of the praseodymium luminescence occurs by cross relaxation which is supposed to be assisted by phonon emission in the case of the³ P ₀ level. Self-quenching of Nd³⁺ luminescence disappears at low temperature indicating that the condition of resonance in the cross-relaxation process is fulfilled only for higher components of the ground state.Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wroclaw, Poland     

The influence of non-radiative transitions on bombardment induced photon emission from Ti and Ti oxide

Photon yields from Ti atoms sputtered from Ti and Ti oxide due to 55 keV Ar⁺ and O₂⁺ ion bombardment have been studied. Photon yields and line profiles of selected lines have also been studied as a function of background O₂ exposure. An attempt has been made to correlate changes in yields and line shapes with variations of the band structure in the solid. Resonance ionization processes are shown not to contribute to the observed yield, however Auger processes cannot be excluded. Lifetime effects have a strong influence on the observed results. It is shown that the distribution of excited states produced by the ion bombardment is Boltzmannlike. We note that it is possible to interpret these results in terms of a model which assumes that the probability of excitation or ionization is exponentially dependent on the excitation or ionization energy, without invoking electron exchange mechanisms.     

Radiative decays of radially excited pseudoscalar mesons in the extended Nambu-Jona-Lasinio model

In the extended NJL model the radiative decay widths of the radially excited states of the pseudo-scalar π, η, and η′ mesons are calculated. The predictions for the decay widths of the processes π(1300) → (ρ⁰, ω)γ, η(1295) → (ρ⁰, ω, φ)γ, and η(1475) → (ρ⁰, ω, φ)γ are given. Nowadays, there are no solid experimental data for these processes. The comparison of the results obtained in the framework of the standard and the extended NJL models for decays of the ground states of mesons is given. It is shown that these calculations correspond to each other and are also in satisfactory agreement with experimental data. This allows one to expect that the extended NJL can give reliable predictions for the excited states of mesons.     

Middle-infrared luminescence of Nd ions in silver halide crystals

The optical absorption and the luminescence emission in the middle infrared (mid-IR) were investigated in AgCl_xBr_1−x crystals doped with Nd³⁺ ions. Strong luminescence emission, in the spectral range 4.5-5.8 μm, in mid-IR was observed for the first time in Nd³⁺-doped silver halide crystals. Various optical parameters were calculated for the Nd³⁺-doped crystals, using the Judd-Ofelt approximation. The measured results and the calculated parameters indicate that these doped crystals could be used for the development of mid-IR solid-state lasers or mid-IR fiber lasers.     

Highly efficient cooperative energy transfer from Ho3+ and Tm3+ ions to Ce3+ ions in crystals

A phenomenon of highly efficient cooperative energy transfer from Ho³⁺ and Tm³⁺ ions to two-particle (2Ce³⁺) cooperative acceptors in crystals of solid solutions of La_1?x Ce _x F₃ is revealed. The rates of cooperative energy transfer in Ho³⁺→2Ce³⁺, Tm³⁺→2Ce³⁺, and Tb³⁺→ 2Yb³⁺ systems are measured, as well as their dependence on the magnitude of the matrix elements of donor transition.     

Spectroscopic characterisation of LaGaO3:Er3+ crystals

LaGaO₃ crystals doped with Er³⁺ ions were grown by the Czochralski method and their optical properties were examined. The Er³⁺ energy levels have been determined from the low-temperature absorption and emission spectra. The results of Judd–Ofelt analysis are presented and compared with experimental data. The emission cross sections are determined for the ⁴ I _13/2→⁴ I _15/2 (1.55 μm) and ⁴ I _11/2→⁴ I _13/2 (2.85 μm) transitions of erbium. Received: 6 December 1999 / Revised version: 10 February 2000 / Published online: 27 April 2000     

Radiative energy transfer from Pb2+ to Eu2+ ions in NaCl,Kcl, and KBr single crystals

In the present work, the emission and excitation spectra of NaCl, KCl, and KBr doubly doped with europium and lead ions were investigated. In all cases, excitation with light lying in the A-band of the Pb²⁺ ions produces in addition to the ³P₁ → ³S_o Pb²⁺ emission, the 4f⁶ 5d (^t2g) → 4f⁷ europium emission. This fact indicates that energy transfer occurs from Pb²⁺ to Eu²⁺ ions. From the data obtained, it was determined that the energy transfer process is of a radiative nature and that it is more efficient in KCl than in either of NaCl or KBr. A possible explanation for this fact is given.