Zero-phonon Transitions Research Articles

Optical properties of silicon-vacancy color centers in diamond created by ion implantation and post-annealing

Silicon-vacancy (SiV) color centers have been created in diamond by ion implantation and post annealing at LABEC (Florence). A wide range of implantation depths (0–2.4 μm) and fluences (108–1015 cm−2), along with a variety of substrates (single and poly-crystals) have been explored. The photoluminescence properties of the SiV centers have been studied at room temperature, including their single-photon emission characteristics. Single-photon emitters have been obtained at the lower-end of the implantation fluences range. They exhibit a short excited-state lifetime (~1 ns), a strong zero-phonon transition with a narrow linewidth (~1.6 nm) and a very small inhomogeneous broadening (0.015 nm), features that qualify them for application in quantum optical technologies. The activation yield of SiV centers has been assessed under different experimental conditions. It has been found to be independent of the implantation energy and in the range of 3% after thermal annealing.

The High-Resolution 4f-5d Absorption Spectrum of Divalent Dysprosium (Dy2+) in Strontium Chloride Host SrCl2: Fine Structure and Zero-Phonon Transitions Revealed.

The virtual lack of information on electronic spectra of divalent lanthanide elements (Ln2+) other than Sm2+, Eu2+, Tm2+, and Yb2+ has prompted us to set for synthesis and characterization of novel Ln2+ systems. First successful attempt concerned SrCl2/Nd2+ single crystals. Here, we report stabilization of divalent dysprosium in a chloride host. Importantly this has been accomplished with Dy ions introduced in a divalent state during synthesis, unlike by γ-irradiation of Dy3+ systems employed previously. This synthesis method yields good quality SrCl2/Dy2+ single crystals. The electronic absorption spectra of Dy2+ doped in SrCl2 have been recorded with high resolution at liquid helium temperature (4.2 K). Identification of the absorption bands occurring in the spectral range of 5000-45000 cm-1 is achieved. On the basis of theoretical calculations using semiempirical Hamiltonian model, assignment of bands and determination of the Hamiltonian parameters for Dy2+(4f95d1) configuration is carried out. The experimental and theoretical studies reveal fine structure and zero-phonon transitions and thus enable high-resolution assignment of spectral lines. It is shown that spin-forbidden transitions gain relatively high intensity due to significant admixing of low-spin character to nominally high-spin states.

Экспериментальное исследование и анализ спектров поглощения ионов Ni-=SUP=-2+-=/SUP=- в ортоборате никеля Ni-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-2-=/SUB=-

AbstractThe results of studies of the absorption spectra of nickel orthoborate Ni_3(BO_3)_2 in the range of electronic d – d -transitions are reported. The obtained data are analyzed in the framework of the crystal field theory. The Ni^2+ ions are located in two crystallographically nonequivalent positions 2 a and 4 f with point symmetry groups C _2 h and C _2, respectively, surrounded by six oxygen ions forming deformed octahedra. The absorption spectra exhibit three intense bands corresponding to spin-resolved transitions from the ground state of nickel ion ^3 A _2 g (^3 F ) to the sublevels of the ^3 T _2 g (^3 F ), ^3 T _1 g (^3 F ) and ^3 T _1 g (^3 P ) triplets split by the spinorbit interaction and the rhombic component of the crystal field. At temperatures below 100 K, the spectra exhibit a thin structure, in which phonon-free lines can be distinguished. Comparison of the calculated frequencies of the zero-phonon transitions with the experimental data allows estimating parameters of the crystal field acting on the nickel ions in the 2 a - and 4 f -positions, as well as the parameters of electrostatic interaction between the 3 d electrons and spin-orbit interaction constants.

Modeling and decoding of fine structure of electron-vibrational 5d – 4f luminescence spectra in LiRF4:Ce3+ (R=Y, Lu) crystals

The 5d-4f luminescence spectra in the LiYF4:Ce3+, LiLuF4:Ce3+ crystals at zero temperature are simulated using a microscopic model of electron-phonon interaction and realistic phonon spectrum of host crystal lattices. Calculations show that three vibrational peaks with the energies 65cm−1, 223cm−1 and 420cm−1 with respect to zero-phonon transition energy dominate in vibrational structure in these spectra. Comparison of simulation results with available experimental data allows to identify zero-phonon lines and vibrational peaks in the measured spectra and thus determine energies of several 4f1 electronic configuration levels: 514, 2221 and 2316cm−1 for LiYF4:Ce3+ and 514, 2188, 2283 and, possibly, 3134cm−1 for LiLuF4:Ce3+ with respect to the ground 4f level energy.

Selective Purcell enhancement of two closely linked zero-phonon transitions of a silicon carbide color center

Point defects in silicon carbide are rapidly becoming a platform of great interest for single-photon generation, quantum sensing, and quantum information science. Photonic crystal cavities (PCCs) can serve as an efficient light-matter interface both to augment the defect emission and to aid in studying the defects' properties. In this work, we fabricate 1D nanobeam PCCs in 4H-silicon carbide with embedded silicon vacancy centers. These cavities are used to achieve Purcell enhancement of two closely spaced defect zero-phonon lines (ZPL). Enhancements of >80-fold are measured using multiple techniques. Additionally, the nature of the cavity coupling to the different ZPLs is examined.

Cooperatively enhanced dipole forces from artificial atoms in trapped nanodiamonds

Since the early work by Ashkin in 1970, optical trapping has become one of the most powerful tools for manipulating small particles, such as micron sized beads or single atoms. The optical trapping mechanism is based on the interaction energy of a dipole and the electric field of the laser light. In atom trapping, the dominant contribution typically comes from the allowed optical transition closest to the laser wavelength, whereas for mesoscopic particles it is given by the bulk polarizability of the material. These two different regimes of optical trapping have coexisted for decades without any direct link, resulting in two very different contexts of applications: one being the trapping of small objects mainly in biological settings, the other one being dipole traps for individual neutral atoms in the field of quantum optics. Here we show that for nanoscale diamond crystals containing artificial atoms, so-called nitrogen vacancy (NV) color centers, both regimes of optical trapping can be observed at the same time even in a noisy liquid environment. For wavelengths in the vicinity of the zero-phonon line transition of the color centers, we observe a significant modification ($10\%$) of the overall trapping strength. Most remarkably, our experimental findings suggest that owing to the large number of artificial atoms, collective effects greatly contribute to the observed trapping strength modification. Our approach adds the powerful atomic-physics toolbox to the field of nano-manipulation.

Optical absorption spectra of the Bi+ impurity center in CsCdBr3 ternary bromide

Optical absorption spectra of the Bi+ impurity center isomorphically substituting Cs+ in CsCdBr3 are recorded over a wide temperature range (from 3.2 to 300 K). An analysis of the vibrational degrees of freedom of the impurity center within the framework of the model of a single effective phonon mode yields various spectroscopic parameters of the optical transition in the Bi+ ion, such as the zero-phonon transition energy, Huang–Rhys parameter, and effective phonon energy. The results are used to compare the properties of the Bi+ center in various crystalline matrices.

The d–f luminescence of Eu2+, Ce3+ and Yb2+ ions in Cs2MP2O7 (M = Ca2+, Sr2+)

The efficient narrow band emission of Eu2+ in Cs2MP2O7 (M = Ca2+, Sr2+) is characterized by a large Stokes shift and a high quenching temperature which makes the material promising for application in warm white LEDs. The unusual Eu2+ luminescence properties were reported recently but an explanation for the peculiar behavior is lacking. In this paper we aim at providing new insights in the luminescence of the Eu2+ emission in Cs2MP2O7 through measurements at cryogenic temperatures (down to 4K) and by comparison with the d–f luminescence of Ce3+ and Yb2+ in the same host. The results reveal a sharp onset of the Eu2+ emission and excitation bands at 4K. Usually the sharp onset for narrow excitation and emission bands coincide at an energy corresponding to the zero-phonon (purely electronic) transition, but for Eu2+ in Cs2MP2O7 there is a large shift of 3500cm−1 between the onsets, consistent with the large Stokes shift observed. The onset shift can be explained by emission from a lower energy distorted excited 4f65d1 state. For Ce3+, the f–d absorption bands are at energies expected based on the relation between the absorption energies for Eu2+ and Ce3+ reported by Dorenbos. Contrary to Eu2+, the emission for Ce3+ shows a normal Stokes shift and therefore the emission bands are at much higher energies than predicted from the energy of the Eu2+ emission and the Dorenbos relations. Based on the present results the unusually large Stokes shift for the Eu2+ emission in Cs2MP2O7 is assigned to a Jahn–Teller like deformation in the excited 4f65d1 state of Eu2+ that is not present in the 5d state of Ce3+.

Quasi-Direct Optical Transitions in Silicon Nanocrystals with Intensity Exceeding the Bulk.

Comparison of the measured absolute absorption cross section on a per Si atom basis of plasma-synthesized Si nanocrystals (NCs) with the absorption of bulk crystalline Si shows that while near the band edge the NC absorption is weaker than the bulk, yet above ∼ 2.2 eV the NC absorbs up to 5 times more than the bulk. Using atomistic screened pseudopotential calculations we show that this enhancement arises from interface-induced scattering that enhances the quasi-direct, zero-phonon transitions by mixing direct Γ-like wave function character into the indirect X-like conduction band states, as well as from space confinement that broadens the distribution of wave functions in k-space. The absorption enhancement factor increases exponentially with decreasing NC size and is correlated with the exponentially increasing direct Γ-like wave function character mixed into the NC conduction states. This observation and its theoretical understanding could lead to engineering of Si and other indirect band gap NC materials for optical and optoelectronic applications.

Hole-Burning Spectroscopy on Excitonically Coupled Pigments in Proteins: Theory Meets Experiment.

A theory for the calculation of resonant and nonresonant hole-burning (HB) spectra of pigment–protein complexes is presented and applied to the water-soluble chlorophyll-binding protein (WSCP) from cauliflower. The theory is based on a non-Markovian line shape theory (Renger and MarcusJ. Chem. Phys.2002, 116, 9997) and includes exciton delocalization, vibrational sidebands, and lifetime broadening. An earlier approach by Reppert (J. Phys. Chem. Lett.2011, 2, 2716) is found to describe nonresonant HB spectra only. Here we present a theory that can be used for a quantitative description of HB data for both nonresonant and resonant burning conditions. We find that it is important to take into account the excess energy of the excitation in the HB process. Whereas excitation of the zero-phonon transition of the lowest exciton state, that is, resonant burning allows the protein to access only its conformational substates in the neighborhood of the preburn state, any higher excitation gives the protein full access to all conformations present in the original inhomogeneous ensemble. Application of the theory to recombinant WSCP from cauliflower, reconstituted with chlorophyll a or chlorophyll b, gives excellent agreement with experimental data by Pieper et al. (J. Phys. Chem. B2011, 115, 405321417356) and allows us to obtain an upper bound of the lifetime of the upper exciton state directly from the HB experiments in agreement with lifetimes measured recently in time domain 2D experiments by Alster et al. (J. Phys. Chem. B2014, 118, 352424627983).

Discrete zero-phonon Cr3+ lines in the spectra of Terbium–Yttrium–Lutetium Aluminum garnets solid solutions: Lattice compression and dilation

Abstract The zero-phonon electronic transitions in Cr 3+ impurity ions in a series of Tb 3 z Y 3 −3 z Al 5 O 12 (0 z 3 x Y 3 −3 x Al 5 O 12 (0 x 2 E– 4 A 2 ) fluorescence spectra of Cr 3+ ions were observed which are not accompanied by strong inhomogeneous broadening, as usually happens in solid solutions. This effect which was first observed in LuYAG and ascribed to high C 3i symmetry of Cr 3+ (Al 3+ ) sites that allows only a limited number of non-equivalent Cr 3+ centers in mixed environment. The energies and radiative lifetimes of 2 E states of locally identical Cr 3+ centers inside different Tb–Y–Lu mixed garnet matrices are studied; the observed dependences on Tb and Lu content are discussed in terms of lattice compression and dilation according to Vegard׳s law. Selective laser spectroscopy confirms the small number of non-equivalent Cr 3+ centers in garnet solid solutions.

Germanium: a new catalyst for diamond synthesis and a new optically active impurity in diamond.

Diamond attracts considerable attention as a versatile and technologically useful material. For many demanding applications, such as recently emerged quantum optics and sensing, it is important to develop new routes for fabrication of diamond containing defects with specific optical, electronic and magnetic properties. Here we report on successful synthesis of diamond from a germanium-carbon system at conditions of 7 GPa and 1,500–1,800 °C. Both spontaneously nucleated diamond crystals and diamond growth layers on seeds were produced in experiments with reaction time up to 60 h. We found that diamonds synthesized in the Ge-C system contain a new optical centre with a ZPL system at 2.059 eV, which is assigned to germanium impurities. Photoluminescence from this centre is dominated by zero-phonon optical transitions even at room temperature. Our results have widened the family of non-metallic elemental catalysts for diamond synthesis and demonstrated the creation of germanium-related optical centres in diamond.

Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback

We report on the feedback stabilization of the zero-phonon emission frequency of a single InAs quantum dot. The spectral separation of the phonon-assisted component of the resonance fluorescence provides a probe of the detuning between the zero-phonon transition and the resonant driving laser. Using this probe in combination with active feedback, we stabilize the zero-phonon transition frequency against environmental fluctuations. This protocol reduces the zero-phonon fluorescence intensity noise by a factor of 22 by correcting for environmental noise with a bandwidth of 191 Hz, limited by the experimental collection efficiency. The associated sub-Hz fluctuations in the zero-phonon central frequency are reduced by a factor of 7. This technique provides a means of stabilizing the quantum dot emission frequency without requiring access to the zero-phonon emission.

Anomalous discrete disorder response of high-symmetry impurity centers spectra in garnet solid solutions.

The zero-phonon electronic transitions in Cr(3+) and Ce(3+) impurity ions in a series of Lu3xY3-3xAl5O12 (0 < x < 1) garnet solid solution crystals were studied experimentally. It was observed that in contrast to the case of Ce(3+), the modification of zero-phonon R-line ((2)E-(4)A2) fluorescence spectra of Cr(3+) ions with changing x occurs in a discrete fashion and is not accompanied by strong inhomogeneous broadening, as usually happens in solid solutions. The effect is ascribed to the high C3i symmetry of the Cr(3+)(Al(3+)) sites that allows only a limited number of non-equivalent Cr(3+) centers in a mixed environment. The energies and radiative lifetimes of the (2)E states of locally identical Cr(3+) centers inside different mixed garnet matrices were studied and the observed dependences on the Lu content x are discussed in terms of lattice compression and dilation.

Deterministic coupling of a single silicon-vacancy color center to a photonic crystal cavity in diamond.

Deterministic coupling of single solid-state emitters to nanocavities is the key for integrated quantum information devices. We here fabricate a photonic crystal cavity around a preselected single silicon-vacancy color center in diamond and demonstrate modification of the emitters internal population dynamics and radiative quantum efficiency. The controlled, room-temperature cavity coupling gives rise to a resonant Purcell enhancement of the zero-phonon transition by a factor of 19, coming along with a 2.5-fold reduction of the emitter's lifetime.

High-resolution infrared spectroscopy of atomic bromine in solid parahydrogen and orthodeuterium

This work extends our earlier investigation of the near-infrared absorption spectroscopy of atomic bromine (Br) trapped in solid parahydrogen (pH2) and orthodeuterium (oD2) [S. C. Kettwich, L. O. Paulson, P. L. Raston, and D. T. Anderson, J. Phys. Chem. A 112, 11153 (2008)]. We report new spectroscopic observations on a series of double transitions involving excitation of the weak Br-atom spin-orbit (SO) transition ((2)P(1/2) ← (2)P(3/2)) in concert with phonon, rotational, vibrational, and rovibrational excitation of the solid molecular hydrogen host. Further, we utilize the rapid vapor deposition technique to produce pH2 crystals with a non-equilibrium mixture of face centered cubic (fcc) and hexagonal closed packed (hcp) crystal domains in the freshly deposited solid. Gentle annealing (T = 4.3 K) of the pH2 sample irreversibly converts the higher energy fcc crystal domains to the slightly more stable hcp structure. We follow the extent of this conversion process using the intensity of the U1(0) transition of solid pH2 and correlate crystal structure changes with changes in the integrated intensity of Br-atom absorption features. Annealing the pH2 solid causes the integrated intensity of the zero-phonon Br SO transition to increase approximately 45% to a value that is 8 times larger than the gas phase value. We show that the magnitude of the increase is strongly correlated to the fraction of hcp crystal domains within the solid. Theoretical calculations presented in Paper II show that these intensity differences are caused by the different symmetries of single substitution sites for these two crystal structures. For fully annealed Br-atom doped pH2 solids, where the crystal structure is nearly pure hcp, the Br-atom SO transition sharpens considerably and shows evidence for resolved hyperfine structure.

Electronic structure and magnetic symmetry in MnTiO3analyzed by second harmonic generation

Second harmonic generation (SHG) and linear absorbance spectra of MnTiO${}_{3}$ were measured and the 1.88, 2.41, 2.63, and 3.06 eV SHG features were identified as $d\ensuremath{-}d$ optical transitions from ${}^{6}{A}_{1g}$ to ${}^{4}{T}_{1g}{(}^{4}G)$, ${}^{4}{T}_{2g}{(}^{4}G)$, ${{}^{4}{E}_{g}$,${}^{4}{A}_{1g}{(}^{4}G)}$, and ${}^{4}{E}_{g}{(}^{4}D)$, respectively. These zero-phonon transitions were used to calculate the octahedral crystal field splitting energy (${\ensuremath{\Delta}}_{0}$) and the Racah parameters $B$ and $C$. The SHG spectra showed significant distinctions between the antiferromagnetic and the paramagnetic or spin-flop phases. The polarization dependence of the SHG in the spin-flop phase provided optical evidence that the spins canted from the $c$ axis toward the $a$ axis. These distinctions between the three magnetic phases could be useful for mapping 180${}^{\ensuremath{\circ}}$ antiferromagnetic domains in MnTiO${}_{3}$.

Phonon-induced dephasing of chromium color centers in diamond

We report on the coherence properties of single photons from chromium-based colour centres in diamond. We use field-correlation and spectral lineshape measurements to reveal the interplay between slow spectral wandering and fast dephasing mechanisms as a function of temperature. We show that the zero-phonon transition frequency and its linewidth follow a power-law dependence on temperature indicating that the dominant fast dephasing mechanisms for these centres are direct electron-phonon coupling and phonon-modulated Coulomb coupling to nearby impurities. Further, the observed reduction in the quantum yield for photon emission as a function of temperature is consistent with the opening of additional nonradiative channels through thermal activation to higher energy states predominantly and indicates a near-unity quantum efficiency at 4 K.

Coupling of Nitrogen-Vacancy Centers to Photonic Crystal Cavities in Monocrystalline Diamond

The zero-phonon transition rate of a nitrogen-vacancy center is enhanced by a factor of ∼70 by coupling to a photonic crystal resonator fabricated in monocrystalline diamond using standard semiconductor fabrication techniques. Photon correlation measurements on the spectrally filtered zero-phonon line show antibunching, a signature that the collected photoluminescence is emitted primarily by a single nitrogen-vacancy center. The linewidth of the coupled nitrogen-vacancy center and the spectral diffusion are characterized using high-resolution photoluminescence and photoluminescence excitation spectroscopy.

Electronic structures of organometallic complexes of f elements LXXIX: Truncated crystal field splitting patterns of monomeric pseudo trigonal planar Yb(η5-C5H4R)3 (R = Me, Et, tBu, SiMe3) complexes and polymeric [(η5-C5H5)2Yb(μ-η5:η1-C5H5)] as well as selected mono adducts

The absorption spectra of pseudo (ψ) trigonal planar tris(methylcyclopentadienyl)ytterbium(III) (Yb(C5H4Me)3) have been recorded at room temperature and circa 77 K. The vibronic transitions were separated from the expected three purely electronic ones by correlating the transition energies with observed and assigned vibrational transition frequencies in the infrared spectrum. With this knowledge, the zero-phonon transitions in the absorption spectra of Yb(C5H4R)3 (R = Et, tBu, SiMe3) and [(η5-C5H5)2Yb(μ-η5:η1-C5H5)] (YbCp3), the latter being known since 1967, could be separated from phonon-assisted ones. The first low temperature luminescence measurements of an organometallic YbIII compound were performed by means of powdered YbCp3•THF and YbCp3•CNC6H11, respectively, and in both cases purely electronic and vibronic transitions were separated. The wavefunctions resulting from a fit of the truncated crystal field splitting pattern of YbCp3•THF allowed interpretation of the spectroscopic splitting factors g||/g⊥ and the temperature dependence of the paramagnetic susceptibility of this compound as well as the susceptibility anisotropy χ|| − χ⊥ of YbCp3•B (B = CNnBu, γ-picoline) and Yb(C5H4Me)3•B (B = CNtBu).