Multiphonon Sideband Research Articles

Multiphonon side band excitation in rare-earth doped fibers and background loss limits

The exponential parameters for Stokes and anti-Stokes side band absorption in ZBLAN : Er3+ fiber and bulk samples have been measured to be 9.4 × 10-3 and 14.1 × 10-3 cm, respectively. Different exponential parameters for side bands absorption and non-radiative decay suggest that different phonons are involved. The influence of side band absorption on the Er3+ doped fiber has been estimated.

Emission spectrum of Ti 3+ :Gd 3Sc 2Al 3O 12 garnet crystal

The photoluminescence spectrum of Ti 3+-doped Gd 3Sc 2Al 3O 12 observed at 77 K and below consists of a series of zero-phonon lines with vibronic structure and a broad band spanning the wavelength range 650 to 1300 nm. By using time-resolved spectroscopy this spectrum has been shown to have overlapping features due to Cr 3+ ions, present as ubiquitous impurities in most garnets, and Ti 3+ ions, as the dominant active species in these crystals. The Cr 3+ impurities are revealed by the zero-phonon lines at 689.2–690.4 nm with attendant phonon-assisted structure. The broadband with peak at 850 nm is identified with the multiphonon sideband of the 2E→ 2T 2 transition of Ti 3+ in trigonally-distorted sites in Gd 3Sc 2Al 3O 12.

Zero-phonon lines in the R 2 absorption of F 3 centres in KF

The zero-phonon line and the structured multiphonon sideband of the R 2 absorption in KF have been investigated in the temperature range 2–100 K. The values of the Huang-Rhys factor (∼2) and of the Debye temperature (241 K) were determined for R 2 transition. Transverse acoustical phonons propagating along 〈100〉 directions are most likely involved in the coupling of the F 3 centres with the KF host lattice.

A zinc-related isoelectronic bound exciton in silicon

Photoluminescence (PL), photoluminescence excitation (PLE), and photoluminescence lifetime measurements are reported for a newly-discovered optical centre in a silicon sample diffused with iron and zinc. The PL spectrum consists of two thermalizing no-phonon lines, each with sharp low energy local mode phonon replicas in addition to a broad multi-phonon sideband. The no-phonon lines, at 1059.93±0.05 and 1075.12±0.05meV, are attributed, respectively, to transitions from the spin triplet and singlet states of an isoelectronic bound exciton (IBE). Other states of the IBE are observed at 1108.4±0.5, 1110.0±0.5 and 1133.2±0.5meV in the PLE spectrum, which also shows sharp local mode phonon replicas. The energy level structure is consistent with IBE states formed by a hole and an electron subject to a large ground state valley-orbit splitting, and bound at the centre by ≈82meV.

Optical Response of Exciton-Phonon System I–Absorption Spectrum and Urbach-Martienssen Rule–

Stochastic theory of the first and second order optical response is presented for a system of exciton-phonon complex. The dynamical motion of the whole lattice system is projected onto the stochastic motion of the relevant modes which interact dominantly with the exciton. In this paper, the dynamical coherent potential approximation is extended to this non-Hamiltonian system and the low energy side of the optical absorption spectrum due to the exciton is studied. It is shown that the multiphonon sidebands are merged into the exponential tail with the increase of the temperature and/or the transfer of the exciton. This exponential tail originates from the thermal distribution of the relevant modes and from the broadening of the phonon sidebands due to the exciton transfer and the interaction with the reservoir of irrelevant lattice vibrations.

Multimode jahn‐teller effect for an E‐Term with strong vibronic coupling II. Band shapes of the infrared and raman spectra

AbstractInfrared and Raman spectra for a Jahn‐Teller (JT) impurity in the E state strongly coupled with crystalline vibrations, as well as vibronic reduction, are investigated. The spectra are shown to represent a superposition of the delta‐like zero‐phonon lines, corresponding to transitions between the rotational levels of the system, with their multiphonon side bands, the latter manifesting the special JT local and resonant states in the crystal density of states, revealed earlier.

Laser photoluminescence of zirconium oxide at 4 K

Laser induced photoluminsecence spectra of ZrO trapped in Ne at 4 K have been obtained. Continuous wave tunable dye and cw argon ion lasers were used to excite ZrO from the X 1Σ+ ground state to the e 1Π and B 3Π electronic states, respectively. Red emission from e 1Π (v=0) →X 1Σ+(v=0,1,2) was observed. In addition, e 1Π (v=0) and e 1Π (v=2) have been found to undergo matrix induced intersystem relaxation into the E 3Π and A 3Φ states, respectively. Infrared emissions of ZrO have been observed and tentatively identified as belonging to E 3Π→X′ 3Δ and e 1Π→c 1Δ. Bandheads of observed transitions are shifted not more than 2% from known gas-phase values. Line shapes of the transitions to the ground state from the e and B states are characterized by a sharp zero-phonon line accompanied by a multiphonon sideband. An additional system overlapping the e 1Π−X 1Σ+ system has been observed and is identified as the A 3Φ2→X′ 3Δ1 band system. The energy of the low-lying c1Δ and X′ 3Δ states are determined to be 5200 and 1650 cm−1 above the ground state.

Laser photoluminescence of TiO in Ne at 4 °K

Pseudo-gas-phase photoluminescence spectra of TiO isolated in Ne matrices at 4 °K have been obtained. Photoluminescence is induced by laser excitation from the X 3Δ ground state to B 3Π and C 3Δ electronic levels using a cw tunable dye laser and a cw argon ion laser, respectively. Red emission from B 3Π vibrational levels terminating in ground state levels is observed. In addition, the B 3Π (v=0) and B 3Π (v=1) levels have been found to undergo matrix-induced intersystem relaxation into the b 1Π state. Near-infrared emission between excited states in the singlet manifold of TiO has been observed and identified as belonging to the δ (b 1Π→a 1Δ) and the φ (b 1Π→d 1Σ+) band systems. Observed δ and φ emission bands are uniformly shifted by −93 cm−1 and +73 cm−1, respectively, from observed or predicted gas phase bandheads. The line shape of the δ and φ emission in the solid is that of a sharp zero-phonon line accompanied by a broad multiphonon sideband. An additional sharp zero-phonon emission system, here labeled the ζ system, is found to overlap several broad multiphonon bands of the red γ′ (B 3Π→X 3Δ) emission. Evidence obtained supports the tentative conclusion that the ζ system is due to intercombination b 1Π→X 3Δ emission. From the assigned intercombination transition the energy of the low-lying a 1Δ state is determined to be 3500 cm−1 above the X 3Δ ground state. The 3500 cm−1 value for the relative energy between the isoconfigurational a 1Δ and X 3Δ states is in qualitative agreement with theoretical expectations based on consideration of the bonding in the TiO molecule.

Near-infrared absorption of MgF 2:Fe 2+

The multiphonon sideband of the spin allowed transition ‖ T 2 g : A 1 − 2〉 → ‖ E g : B 3 − 2〉 within the 3 d 6 orbital of Fe 2+ in D 2 h symmetry was analyzed with respect to the one phonon absorption and density of states of the coupled phonon modes. Temperature dependence of the zero-phonon line shows, that the axial anisotropy of the S = 2 spin multiplet in the excited B 3 state is about 0.9 cm -1.

Phonon Sidebands in the Emission Spectrum ofO2−in Alkali-Halide Crystals

The emission spectra of $\mathrm{O}_{2}^{}{}_{}{}^{\ensuremath{-}}$ ions dissolved in alkali-halide crystals consist of a series of zero-phonon lines each accompanied by multiphonon sidebands. We present high-resolution measurements of such emission spectra at 2 \ifmmode^\circ\else\textdegree\fi{}K in the alkali halides NaCl, KCl, KBr, KI, RbCl, RbBr, and RbI. The zero-phonon lines are due to vibronic transitions within the $\mathrm{O}_{2}^{}{}_{}{}^{\ensuremath{-}}$ molecule, and the sidebands are produced by the interaction of even-parity lattice modes with the allowed ${\ensuremath{\Pi}}_{g}\ensuremath{\leftarrow}{\ensuremath{\Pi}}_{u}$ transition corresponding to the $\mathrm{O}_{2}^{}{}_{}{}^{\ensuremath{-}}$ emission. We show that most of the sideband structure can be explained by coupling with ${A}_{1g}$ lattice modes perturbed by relatively small changes in nearest-neighbor force constants. In two cases (KCl and RbCl) it is necessary to add ${T}_{2g}$ modes, or to consider changes in other force constants, to obtain better agreement between calculated and observed sidebands. A residual spectrum at very low frequencies cannot be explained by the above hypothesis; it is assigned to a second-order coupling to librations of the $\mathrm{O}_{2}^{}{}_{}{}^{\ensuremath{-}}$ ion. Some broad features in the emission spectra are interpreted in terms of transitions to short-lived low-lying electronic states.

Two phonon processes and phase transitions in KMnf 3: Temperature discontinuities in the I.R. Spectrum and group theoretical analysis

The far i.r. reflection spectrum of KMnF 3 single crystals was measured for various temperatures between 65°K and room temperature. A multi-phonon sideband near 261 cm −1 was observed in the low temperature spectra, showing marked temperature discontinuities of the intensity at 88°K = Néel temperature and 190°K ( = temperature of the transition from cubic to orthorhombic phase). At 190°K, the sideband disappears abruptly. The group theoretical study of two-phonon processes in KMnF 3 suggests an interpretation in terms of symmetry dependent multiphonon selection rules. Careful analysis of the behaviour of the critical points of the first Brillouin zone at the phase transition from O h 1 to D 16 2 h shows the existence of R and M processes forbidden in the higher and allowed in the lower symmetry phase. A precise assignment of the reflection band can, however, not be given.

Luminescent Transitions Associated With Divalent Copper Impurities and the Green Emission from Semiconducting Zinc Oxide

Luminescent transitions at divalent copper impurities in ZnO give rise to a close-spaced, no-phonon doublet at \ensuremath{\sim}2.8590 eV, as well as a broad multiphonon side band. The transition is found to be an optical charge transfer between a highly shielded localized level of the copper impurity and a level which is strongly perturbed by the valence-band states of the crystal. The analysis provides information about the role of deep acceptor states in electronic processes in covalent solids.