Pairs In Ruby Research Articles

Time-resolved photo-phonon spectroscopy of exchange coupled Cr3+ pairs in ruby

A rather simple method is used to simultaneously detect both optical absorption spectra and excited-state nonradiative transitions in 0.03 and 0.16 at. % ruby at temperature 2 K. The technique utilizes a time-resolved bolometer detection of phonons generated by the excited-state nonradiative relaxation following optical excitation with a pulsed tunable dye laser. The observed excitation spectra of phonons coincide well with currently known absorption spectra of both chromium single ions and pairs of the nearest neighbors. For the first time, the fast (≤ µs) resonant energy transfer from single chromium ions to the fourth nearest neighbors is observed directly. New strongly perturbed Cr-single-ion sites are observed.

Theoretical Calculation for Multiplet Structure of Chromium Ion Pair in Ruby

We have recently developed a general method for the calculation of electronic structures including many-electron interaction from first principles, which we call DV-ME method. In this paper, we report on its application to the calculations for multiplet structures of chromium ion pairs in ruby. The first and fourth nearest neighbour ion pairs were considered by the use of [CrCrAl 2 O 16 ] 20- model clusters. The results qualitatively reproduced not only the multiplet energies of the pair of ground-state chromium ions, but also those of the excited states arising from the spin-flip and charge-transfer transitions. The state with the minimum energy in the ground-state pair showed that the first nearest neighbour ion pair is antiferromagnetically coupled and the fourth nearest neighbour ion pair is ferromagnetically coupled. From the energy levels in the ground-state pairs, the exchange integrals Jare also evaluated. The calculated signs of J are consistent with the results from experiments, indicating that the exchange integral J in the classical Heisenberg Hamiltonian can be calculated by first-principles calculation.

Energy transfer between different emitters and spatial diffusion in ruby

The energy transfer between single Cr3+ ions and N2 pairs in ruby is interpreted by energy diffusion on single ions. It is shown that the superexchange is responsible for this diffusion. The probability of transfer between single ions and the diffusion coefficient are evaluated. Experimental results on the transfers from fourth next-neighbour pairs to single ions and to third next-neighbour pairs are given. It appears that the diffusion is weak on the fourth NN pairs. The temperature dependence of the transfer probabilities are determined and interpreted.

Energy migration in ruby and transfer to the N-line traps

The technique of chronospectroscopy has been used to determine the rate constant for energy transfer from single ions to pairs in ruby. Because of the dependence of the rate on concentration, the exchange transfer processes are observable directly as postulated by several authors. The temperature dependence shows that transfer occurs by energy migration between single ions.

Piezo-spectroscopic investigations on the first and second nearest exchange coupled Cr 3+-pairs in ruby

The dependence on distance of the exchange integrals J was investigated for the first and second nearest Cr 3+-pairs in ruby by uniaxial pressure along the C 3-axis. With the experimentally determined values of ΔJ Δr , the corresponding exchange integrals in ruby and Cr 2O 3 could be assimilated and the biquadratic term in the exchange interaction could be explained by exchange striction.

The first and second nearest neighbour Cr3+ pairs in ruby

The first and second nearest neighbour Cr3+ pairs in ruby

The first and second nearest neighbour Cr3+ pairs in ruby

The irreducible representations of the states of the first and second nearest neighbour Cr3+ pairs in ruby were deduced from the known states of the single ions by the group theoretical method of induction. The summetry selection rules and polarizations for electric dipole radiation are discussed.

Infra-red light absorption in chromium ion pairs in ruby

A qualitative explanation of experimentally observable far-infrared absorption lines due to transitions between the ground state energy levels of exchange-coupled Cr 3+ ion pairs in ruby is given on the basis of assuming the electro-dipole character of these transitions.

Spectrum of first-nearest-neighborCr3+pairs in ruby

The optical absorption, emission, and excitation spectrum and the exchange splittings of the first-neighbor ${\mathrm{Cr}}^{3+}$ pairs in ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ have been studied. The earlier experimental level assignment is shown to be inconsistent with the theory of Pryce and Naito. The new ground-state level scheme is based on the $\ensuremath{\sigma}$-polarized fluorescence line at 7301.5 \AA{} which terminates on the $S=2$ level, which is \ensuremath{\sim}280 ${\mathrm{cm}}^{\ensuremath{-}1}$ above the $S=0$ level, and the $\ensuremath{\pi}$-polarized transition to the $S=3$ level at 7367.5 \AA{}. The new parameters of the ground-state exchange $J({\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}}_{1}\ifmmode\cdot\else\textperiodcentered\fi{}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}}_{2})+j{({\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}}_{1}\ifmmode\cdot\else\textperiodcentered\fi{}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}}_{2})}^{2}$ are $J=54$ and $j=\ensuremath{-}8.7$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The infrared pair transitions obtain their strength mainly from the single-ion mechanism. The weakness of the exchange-induced dipole moment, which usually dominates in pair spectra, is attributed to a near cancellation of the single-electron components. A comparison of the relative $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ intensities suggests that the odd-parity crystal field is somewhat different than for single ions. Transitions where both ions of the pair are excited to the $^{2}E$ states have been observed at nearly twice the $R$-line energy. The $\ensuremath{\sigma}$ polarization of these transitions agrees with the exchange-induced dipole-moment mechanism. The temperature dependence of the absorption of the $S=0 \mathrm{and} 1$ levels is in good agreement with the level populations derived from the ground-state exchange splittings.

Chronospectroscopy of Exchange-CoupledCr3+-Ion Pairs in Ruby

A rather simple method of determining the lifetimes of the excited states of exchange-coupled ion pairs in ruby is described. The technique utilizes a chopped pump light and phasesensitive detection. It has permitted a great increase in the resolution of optical transitions, and in particular, it allows for a virtual elimination of the vibronic sidebands of the $R$ lines, in order that the true pair spectrum may stand out clearly. Furthermore, transitions originating from different excited levels may be definitely distinguished, thus aiding in the identification of particular transitions with a given pair type. The chronospectroscopic method is of potential value in the studies of energy-transfer mechanisms between single ions and pairs. It has also provided evidence for a fourth-neighbor absorption band at 6050 \AA{}.

Higher Energy Levels of Cr3+ Ion Pairs in Ruby and Lanthanum Aluminate

AbstractThe excitation and absorption spectra were investigated of the doubly excited states |2E × 2E〉, |2E × 2T1〉, |2T1 × 2T1〉 × 2T1, and |2E×2T2 of the first nearest neighbour Cr3+ ion pairs in LaAlO3, and of the first, second, third, and fourth nearest neighbour Cr3+ pairs in ruby. The spectra were analyzed for electronic and vibronic transitions.

Direct optical excitation into excited states of Cr 3+ pairs in ruby

Relative intensities of red fluorescence lines in ruby were found to depend on the exciting light wavelength. Excitation spectra for the N 1 and N 2 emission lines measured with a tunable dye laser showed narrow lines in the 460–490 nm wavelength region. They are assigned to the 4 A 2 4 A 2 → 4 A 2 2 T 2 transitions in exchange-coupled chromium ion pairs.

Energy levels of chromium ion pairs in ruby

A comment on papers of Kisliuk and coworkers and of Joyce and Richards is given. According to these papers, direct transitions between the ground state energy levels of exchange-coupled Cr 3+- pairs in ruby are strictly forbidden. Experimental and theoretical evidence is reported which, however, is in favor of the existence of at least a few weak far-i.r. absorption lines due to such transitions. In addition, the origin of two non-exchange absorptions is discussed.

On the effect of exchange interaction on the impurity ion optical spectrum

AbstractThe method of effective Hamiltonian (EFH) is applied to the excited state (2E4A2) fine structure of Cr3+–Cr3+ fourth order pairs in ruby. Comparison with experimental data illustrates the importance of both the anisotropic and antisymmetric exchange interactions, and that part of isotropic exchange interaction, which is nondiagonal in the orbital variables. Various microscopical mechanisms responsible for terms in the effective Hamiltonian are discussed.

Energy transfer and rate equations—application to ruby

AbstractAtomistic rate equations are represented for the transfer of optical excitation energy between donor and acceptor ions in ionic crystals. The physical assumptions which are necessary to deduce the phenomenological collective rate equations from the atomistic ones are specified. Time resolved measurements of the energy transfer from isolated Cr3+ ions to Cr3+ pairs in ruby are discussed. It is shown that, contrary to the present ideas, the collective rate equations cannot be applied in this case.

Optical and Electron-Spin-Resonance Studies of Fourth-Nearest-Neighbor Chromium Ion Pairs in Ruby

The fine structure of the optical fluorescence spectrum arising from the fourth-nearest-neighbor chromium ion pair system in ruby is studied using high-resolution optical spectroscopy, ordinary electron-spin resonance, and optically detected electron-spin resonance. The ground-state energy levels of this system are found to be describable by a simple spin Hamiltonian of the form $\mathcal{H}=g\ensuremath{\beta}\mathbf{H}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{S}+\frac{J}{2}[S(S+1)\ensuremath{-}\frac{15}{2}]+{D}_{S}[S_{z}^{}{}_{}{}^{2}\ensuremath{-}\frac{1}{3}S(S+1)]+{E}_{S}[S_{x}^{}{}_{}{}^{2}\ensuremath{-}S_{y}^{}{}_{}{}^{2}]$ where the directions of the symmetry axes, ${D}_{S}$, and ${E}_{S}$ each depend on the spin $S$ in a predictable way, requiring only two adjustable parameters: ${D}_{c}$ (the usual second-order crystal-field term of axial symmetry) and ${D}_{E}$ (a similar term arising from the anisotropic exchange interaction). The value of ${D}_{c}$ is found to be -0.191\ifmmode\pm\else\textpm\fi{}0.005 ${\mathrm{cm}}^{\ensuremath{-}1}$, which is equal to that for the isolated ion. The value of ${D}_{E}$ is found to be -0.021\ifmmode\pm\else\textpm\fi{}0.005 ${\mathrm{cm}}^{\ensuremath{-}1}$. A phonon-assisted energy-transfer mechanism is postulated to account for the existence of the optically detected spin-resonance spectrum.

Energy Levels of Chromium Ion Pairs in Ruby

Abstract : The lower energy levels of a number of transitions due to second, third, and fourth nearest neighbor chromium ion pairs in ruby are located by measuring the temperature dependence of optical absorption. Energy level diagrams are constructed, from which many of the observed lines are identified. The measurements are consistent with earlier results for the ground states of first, third,, and fourth nearest neighbor pairs. The ground-state levels of the second nearest neighbor pairs are describable by an isotropic exchange interaction. The ground-state coupling parameters for the first four nearest neighbor types are used to estimate the Neel and Curie-Weiss temperatures for Cr2O3. (Author)

EPR in the Excited Optical States of Exchange-Coupled Chromium Ion Pairs in Ruby

By means of an optical detection technique, we have studied EPR in the excited metastable optical level of exchange-coupled chromium ion pairs in ruby with concentration of ∼0.2% Cr2O3. In such excited pair states one ion is in an excited optical state while the other is in its ground state. We have confined our attention mainly to fourth-nearest-neighbor pairs. We find evidence that when one ion of the pair is excited, it is antiferromagnetically coupled to its fourth-nearest-neighbor, while both ions are ferromagnetically coupled in the ground state. In the optical detection method we monitor the fluorescence from the particular center being studied and note the change in fluorescence signal which occurs when resonant microwave power changes the population in the excited state. Besides the resonance signals expected from our knowledge of the excited pair state, we find a number of additional resonances. Some of these have been identified as single chromium ion resonances which affect the pair fluorescence because of the transfer of optical excitation from single ion to pair. The other signals appear to be fourth-nearest-neighbor ground-state resonances which are detected because of their effect upon the optical pumping of the pair.

Consideration of Polarization and Covalency Corrections to the Quasi‐Coulomb Shift of Optical Lines of Ion Pairs in Crystals

AbstractThe effect of polarization and covalency corrections on the Coulomb interaction of impurity ion pairs in ionic crystals is taken into account. A simple semi‐empirical theory is suggested for the explanation of the quasi‐Coulomb shifts of the optical lines belonging to the pairs of equivalent impurity ions (in relation to the corresponding lines of single impurity ions). In this theory we use effective charges and effective electric dipole moments of ions. The theory is applied to the explanation of the optical spectrum of Cr3+Cr3+ pairs in ruby. The problem of a microscopical calculation of effective parameters is discussed.

Symmetry properties and magnetic resonance of exchange coupled ion pairs

Symmetry properties of pairs of identical exchange-coupled ions isolated in a diamagnetic host crystal are studied. Starting from a spin Hamiltonian allowing for exchange interaction, crystal-field and Zeeman splitting, the forms of the various coupling tensors for all possible symmetries are determined. Unitary transformations of the spin Hamiltonian and their influence on the coupling tensors are discussed. Asymmetric exchange-coupling tensors arise only on few occasions. Selection rules for magnetic dipole transitions are given for systems with high symmetry. As an example, magnetic resonances due to Cr 3+ pairs in ruby are considered.