Earth Ions In Crystals Research Articles

Quantum computation of the lowest-energy Kramers states and magnetic g-factors of rare earth ions in crystals

Quantum computation of the lowest-energy Kramers states and magnetic g-factors of rare earth ions in crystals

Insight into the thermal shifts of ten fluorescence peaks Y1–Y10 for Sm3+ ions in Y3Al5O12 crystal

The observed linear thermal shifts of ten fluorescence peaks Y1–Y10 from room temperature to about 1000 K for Y3Al5O12:Sm3+ (grown by the Czochralski method) were investigated by considering both the static effect owing to lattice thermal expansion and the dynamic effect stemming from electron–phonon interaction. The static effects were acquired by using the pressure dependences of these fluorescence peak positions. The static effects for the ten fluorescence peaks resulted in thermal blue shift, but the dynamic effects for all peaks except Y7 led to thermal red shift. The observed nature of thermal shift (i.e. red or blue) of a fluorescence peak was due to competition between the static and dynamic effects. Based on an approximate treatment, the static parameter A (characterizing the static effect) and electron–phonon coupling parameter αʹ (characterizing the dynamic effect) for these fluorescence peaks were estimated in the case where thermal shift curves from low temperature to near or higher than room temperature were not measured. Parameters A for all fluorescence peaks and αʹ for all peaks except Y7 were comparable in sign and magnitude with those of the sharp luminescence peaks of other rare earth ions in crystals and so were deemed to be reasonable. The causes of the exception for αʹ of Y7 spectral peak (including the very large observed thermal blue shift of this peak) remain unclear.

Spectroscopic detection of single Pr3+ ions on the 3H4−1D2 transition

Rare earth ions in crystals exhibit narrow spectral features and hyperfine-split ground states with exceptionally long coherence times. These features make them ideal platforms for quantum information processing in the solid state. Recently, we reported on the first high-resolution spectroscopy of single ions in yttrium orthosilicate nanocrystals via the transition at a wavelength of 488 nm. Here we show that individual praseodymium ions can also be detected on the more commonly studied transition at 606 nm. In addition, we present the first measurements of the second-order autocorrelation function, fluorescence lifetime, and emission spectra of single ions in this system as well as their polarization dependencies on both transitions. Furthermore, we demonstrate that by a proper choice of the crystallite, one can obtain narrower spectral lines and, thus, resolve the hyperfine levels of the excited state. We expect our results to make single-ion spectroscopy accessible to a larger scientific community.

Single molecule fluorescence resonance energy transfer scanning near-field optical microscopy: potentials and challenges.

A few years ago, single molecule Fluorescence Resonance Energy Transfer Scanning Near-Field Optical Microscope (FRET SNOM) images were demonstrated using CdSe semiconductor nanocrystal-dye molecules as donor-acceptor pairs. Corresponding experiments reveal the necessity to exploit much more photostable fluorescent centers for such an imaging technique to become a practically used tool. Here we report the results of our experiments attempting to use nitrogen vacancy (NV) color centers in nanodiamond (ND) crystals, which are claimed to be extremely photostable, for FRET SNOM. All attempts were unsuccessful, and as a plausible explanation we propose the absence (instability) of NV centers lying close enough to the ND border. We also report improvements in SNOM construction that are necessary for single molecule FRET SNOM imaging. In particular, we present the first topographical images of single strand DNA molecules obtained with fiber-based SNOM. The prospects of using rare earth ions in crystals, which are known to be extremely photostable, for single molecule FRET SNOM at room temperature and quantum informatics at liquid helium temperatures, where FRET is a coherent process, are also discussed.

Spectroscopic detection and state preparation of a single praseodymium ion in a crystal.

The narrow optical transitions and long spin coherence times of rare earth ions in crystals make them desirable for a number of applications ranging from solid-state spectroscopy and laser physics to quantum information processing. However, investigations of these features have not been possible at the single-ion level. Here we show that the combination of cryogenic high-resolution laser spectroscopy with optical microscopy allows one to spectrally select individual praseodymium ions in yttrium orthosilicate. Furthermore, this spectral selectivity makes it possible to resolve neighbouring ions with a spatial precision of the order of 10 nm. In addition to elaborating on the essential experimental steps for achieving this long-sought goal, we demonstrate state preparation and read out of the three ground-state hyperfine levels, which are known to have lifetimes of the order of hundred seconds.

Impurity trapped exciton states related to rare earth ions in crystals under high hydrostatic pressure

Emission related to rare earth ions in solids takes place usually due to 4fn → 4fn and 4fn−15d1 → 4fn internal transitions. In the case of band to band excitation the effective energy transfer from the host to optically active impurity is required. Among other processes one of the possibilities is capturing of the electron at excited state and hole at the ground state of impurity. Localization of electron or hole at the dopand site creates a long range Coulomb potential that attracts the second carrier which then occupies the localized Rydberg-like states. Such a system can be considered as impurity trapped exciton. Usually impurity trapped exciton is a short living phenomenon which decays non-radiatively leaving the impurity ion in the excited state. However, in several compounds doped with Eu2+ the impurity trapped exciton states become stable and contribute to the radiative processes though anomalous luminescence that appears apart of the 4f7 → 4f7 and 4f75d1 → 5f7 emission. In this contribution pressure effect on energies of the 4fn−15d1→5fn transitions in Ln doped oxides and fluorides as well as influence of pressure on the energy of impurity trapped exciton states is discussed. The latest results on high pressure investigations of luminescence related to Pr3+, and Eu2+ in different lattices are reviewed.

Polarization selection rules and optical transitions in terbium activated yttrium tantalate phosphor under x-ray, vacuum-ultraviolet, and ultraviolet excitations

The terbium-activated yttrium tantalite (YTaO(4):Tb(3+)) phosphor is of great interest due to the interesting spectroscopic properties of rare earth ions in crystals and also practical use in x-ray imaging. Using the group-theoretical approach, we analyze the selection rules for the transition between Stark components of Tb(3+) in symmetry of the actual crystal field and the polarization for the allowed transitions. The luminescence upon UV, vacuum-ultraviolet (VUV), and x-ray excitation is presented and discussed. The YTaO(4):Tb(3+) phosphors are found to be efficient VUV-excited luminescent materials that could be used not only in x-ray intensifying screens, but also in mercury-free fluorescent lamps or plasma display panels.

Electron paramagnetic resonance spectroscopy of Er3+:Y2SiO5 for coherent optical applications

Abstract Electron paramagnetic resonance spectroscopy of rare earth ions in crystals is an interesting tool to analyze the hyperfine structure of the rare earth ground state. This can be useful for coherent spectroscopy and quantum information applications where the hyperfine structure of the electronic levels is used. In this work, we give a detailed analysis of the hyperfine structure of the ground state ( I 4 15 / 2 ( 0 ) ) of Er3+ ions in Y2SiO5.

Orange avalanche upconversion for high-resolution laser spectroscopy

High resolution spectroscopy of quantum systems is a key point in the quantum information field. Rare earth ions in crystals are interesting candidates for this application because of the long coherence lifetime of some of their transitions. These ions can also be manipulated by optical excitation which has, however, to be produced by ultra-stable laser sources. This proves to be a very difficult task in the case of dye lasers which are necessary to excite Pr3+ doped crystals and especially Pr3+:Y2SiO5. This compound is by far the most used host in rare earth based quantum information studies. In this paper, we discuss the use of Pr3+,Yb3+ codoped materials to build an infrared pumped solid state laser suitable to excite Pr3+:Y2SiO5 around 606 nm. We show by the analysis of a rate equation model that avalanche upconversion is not very efficient to obtain a high power laser. This is more easily obtained if a second laser is set to pump resonantly Yb3+ ions. The spectroscopic properties of a new matrix Pr3+,Yb3+:PbF2 are also investigated. We found that this compound emits at 606.18 nm with a width of 5 nm and would be therefore suitable to excite Pr3+:Y2SiO5. Moreover, it can be excited at 857 nm and 975 nm, i.e. in the range of high power laser diodes.

Hyperfine interaction ofEr3+ions inY2SiO5: An electron paramagnetic resonance spectroscopy study

Electron paramagnetic resonance (EPR) spectroscopy of rare earth ions in crystals is a powerful tool to analyze the hyperfine structure of the rare earth ground state. This can be useful for coherent spectroscopy and quantum information applications where the hyperfine structure of the electronic levels is used. In this work, we give a detailed analysis of the hyperfine structure of the ground state $[^{4}I_{15∕2}(0)]$ of ${\mathrm{Er}}^{3+}$ ions in ${\mathrm{Y}}_{2}\mathrm{Si}{\mathrm{O}}_{5}$. The electronic Zeeman, hyperfine, and quadrupole matrices are obtained from angular variations of the magnetic field in three orthogonal crystal planes. An excellent agreement is obtained between experimental and simulated magnetic field positions and relative intensities of EPR lines.

Magnetic dipole transitions in crystals

The magnetic dipole transitions in rare earth ions in crystals are described in terms of a model based on the fourth order perturbation theory. An analysis of the perturbing influence of crystal field potential and spin-orbit interaction is made. In addition to intra-shell interactions, inter-shell interactions that include the influence of the excited configurations are analysed. The transition amplitude is defined in terms of effective operators expressed by double unit tensor operators. The radial integrals of all effective operators are defined within the perturbed function approach, therefore the complete radial basis sets of one-electron states of given symmetry are taken into account. Conclusions mainly focus on the possible importance of magnetic dipole transitions in the description of electric dipole 0 ⟷ 0 transition due to the so-called borrowing mechanism.

Magnetic Linear Birefringence in Rare Earth Systems. II. Third-Order Approach

The theory of linear magnetic birefringence of rare earth ions in crystals is extended here by the contributions that represent a direct perturbing influence of the crystal field potential surrounding the central ion. The basic assumptions of the theoretical model are the same as in the previous analysis of second-order terms. The third-order contributions introduced here break the free ionic system approximation, and they represent the impact due to configuration interaction. The effective operators include the perturbing influence of the excitations from the 4f shell to one-electron states of the same parity (as previously at the second order), and in addition, the excitations to states of opposite parity. All contributing terms are expressed by the effective operators that are defined within the perturbed function approach. The tensorial structure of these operators is discussed, and special attention is directed to newly defined radial integrals. The values of all radial integrals that are necessary for the third-order numerical analysis are presented in the case of all lanthanide ions.

A simple model for f→d transitions of rare-earth ions in crystals

Theoretical simulation and interpretation of f→d transitions of rare earth ions in crystals are more difficult than for f→f transitions, because f→d transitions involve many more energy levels and are further complicated by strong vibronic transitions, so the experimental spectra contain many fewer resolvable peaks. In order to better understand the structure of the spectra, a simple model is developed to take into account the main interactions in the fN−1d configuration. This model leads to quantum numbers characterizing the states and the associated transition selection rules. Relative transition intensities can be quantitatively estimated. The model is applied to Eu2+ and Sm3+ ions in crystals.

Rare earth doped yttrium aluminum garnet (YAG) selective emitters

As a result of their electron structure, rare earth ions in crystals at high temperature emit radiation in several narrow bands rather than in a continuous blackbody manner. This study presents a spectral emittance model for films and cylinders of rare earth doped yttrium aluminum garnets. Good agreement between experimental and theoretical film spectral emittances was found for erbium and holmium aluminum garnets. Spectral emittances of films are sensitive to temperature differences across the film. For operating conditions of interest, the film emitter experiences a linear temperature variation whereas the cylinder emitter has a more advantageous uniform temperature. Emitter efficiency is also a sensitive function of temperature. For the holminum aluminum garnet film the efficiency is 0.35 at 1446 K, but only 0.27 at 1270 K.

Rare earth doped high temperature ceramic selective emitters

As a result of their electron structure, rare earth ions in crystals at high temperature emit radiation in several narrow bands rather than in a continuous blackbody manner. This study develops a spectral emittance model for films of rare earth containing materials. Although there are several possible rare earth doped high temperature materials, this study was confined to rare earth aluminum garnets. Good agreement between experimental and theoretical spectral emittances was found for erbium, thulium and erbium–holmium aluminum garnets. Spectral emittances of these films are sensitive to temperature differences across the film. Emitter efficiency is also a sensitive function of temperature. For thulium aluminum garnet the efficiency is 0·38 at 1700 K but only 0·19 at 1262 K.

Relativistic contributions to the amplitude of electric dipole transitions in rare earth ions in crystals: I. Spin-orbit interaction

The third-order contributions to the amplitude of transitions caused by spin-orbit interaction are analysed. The atomic-like properties of the perturbed functions which are the first-order corrections to the free ion radial functions are discussed in the context of the lanthanide contraction. In addition, the values of the radial terms of the spin-orbit effective operators evaluated for complete radial basis sets of one-electron functions of given symmetry are presented for several lanthanide ions.

Uniform perturbation approach of the theory of one- and two-photon f↔ f transitions

A consistent theoretical background of published approaches, uniform for one- and two-photon electric dipole transitions in rare earth ions in crystals, is presented. Due to the special electronic structure of trivalent rare earth ions, the theoretical description of their spectroscopic properties is based on perturbation theory. In particular, Rayleigh–Schrödinger perturbation theory is applied, and the perturbing expansion of the wave functions is limited to second-order corrections. In the discussion of various models of f↔ f transitions special attention is directed to the detailed definition of the Hamiltonian and to partitioning of the space. The general expressions for various kinds of contributions to the transition amplitude are presented, including the perturbing influence of the crystal field potential, electron correlation effects and spin–orbit interaction.

Are the odd-rank crystal field parameters independent quantities?

The relation between various odd-rank crystal field parameters is discussed in the context of the theoretical description of the spectroscopic properties of rare earth ions in crystals.

Theoretical description of the spectroscopic properties of rare earth ions in crystals

In this article the present state of knowledge of the theory of one- and two-photon processes observed in rare earth ions in crystals is presented. The conclusions are based on the results of ab initio calculations performed for various ions across the lanthanide series. The model applied for the calculations is based on the Rayleigh–Schrödinger perturbation theory, and the amplitude of a certain electric dipole transition is expressed in terms of effective operators. The radial integrals of the effective operators are defined by the perturbed functions that contain the perturbing influence of single excitations from the 4f shell to all one-electron states of a given symmetry, discrete and continuum. In this approach the interactions between the 4f N and the excited configurations via the crystal field potential, the electron correlation operator and the spin–orbit interaction operator are discussed; it is believed that the presented theory contains the most important physical mechanisms responsible for the f↔f electric dipole transitions. Two alternative formulations of the theory of one-photon electric dipole transitions are presented. Consequently, the transition amplitude is defined within the standard theory based on the length formula and within a new approach which is based on the velocity form of the electric dipole radiation operator.

Rare Earth Doped Yttrium Aluminium Garnet (YAG) Selective Emitters

AbstractAs a result of their electron structure, rare earth ions in crystals at high temperature emit radiation in several narrow bands rather than in a continuous blackbody manner. This study presents a spectral emittance model for films and cylinders of rare earth doped yttrium aluminum garnets. Good agreement between experimental and theoretical film spectral emittances was found for erbium and holmium aluminum garnets. Spectral emittances of films are sensitive to temperature differences across the film. For operating conditions of interest, the film emitter experiences a linear temperature variation whereas the cylinder emitter has a more advantageous uniform temperature. Emitter efficiency is also a sensitive function of temperature. For holminum aluminum garnet film the efficiency is 0.35 at 1446K but only 0.27 at 1270 K.