States Of Er3 Research Articles

Energy transfer to Er 3+ ions in a‐Si 1− x C x :H alloys: emission at 1.54 mm wavelength

The energy transfer to Er3+ ions in a-Si1−xCx:H films has been studied by absorption, luminescence and magnetic resonance spectroscopy. Erbium is incorporated either by magnetron assisted co-sputtering of Si and Er in a silane plasma or by conventional plasma deposition of a metalorganic compound which yields films of very different defect density and Er environment. The data confirm Er ions as efficient radiative recombination centres in a-Si:H, which are excited by resonant energy transfer from electron hole pairs in the host and disprove that dangling bonds are needed for emission at 1.5 μm wavelength by Erbium ions. We propose a Forster energy transfer, which is based on resonant dipole coupling. Resonance to excited states of Er3+ is achieved as electrons thermalise in tail states and form pairs with localized holes and enables rapid energy transfer to Erbium ions while back transfer is inefficient due to lattice relaxation. Thermalisation and recombination rates in the host material control the excitation of Er ions and can be modified by alloying silicon with carbon. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Defect-mediated and resonant optical excitation of Er3+ ions in silicon-rich silicon oxide

Sensitization of the 4I13/2–4I15/2 Er3+ luminescence at 1.54 μm in silicon-rich silicon oxide (SRSO) is studied in the blue-green range. We show that defects due to excess Si in silica act as luminescence sensitizers. We also suggest that there exist two types of Er centers—isolated ones and others—strongly coupled to defects. In SRSO competition of direct, resonant excitation of Er3+ and indirect processes via defects is observed. Enhancement of the Er emission for off-resonant excitation does not seem to compensate losses in the direct channel of excitation to the 2H11/2 state of Er3+. We suggest that the emission efficiency of Er3+ is limited by distance-dependent transfer rate and little spectral overlap of the interacting states.

Confinement on energy transfer between luminescent centers in nanocrystals

The luminescence dynamics of optical centers in nanocrystals depends critically on the phonon density of states (PDOS), which is quite distinct from that of bulk materials. It is shown that energy transfer (ET) in nanocrystals is confined by discrete PDOS as well as direct size restriction. Temperature-, concentration-, and size-dependence of the fluorescence decay from the S3/24 state of Er3+ in Y2O2S nanocrystals have been investigated using laser spectroscopic experiments and computational simulations. A set of microscopic rate equations that govern the evolution of the excitation probability Pi(t) are solved iteratively using a Monte Carlo method. The simulations of ET based on a theoretical model with five parameters are in good agreement with the experimental results. It is shown that phonon-assisted ET processes in Er3+:Y2O2S nanocrystals contribute partly to the fluorescence decay at 295 K, and is negligible at 5 K. For applications, the nanoconfinement effects on ET may significantly reduce the efficiency of sensitized or upconversion luminescence due to the lack of low-frequency phonon modes and restricted excitation migration in nanophosphors.

The absorption spectra of gallium nitride crystals doped with erbium ions

We have measured the absorption spectra of Er3+ ions introduced by diffusion into bulk GaN crystals grown by vapor phase epitaxy in a chloride system. The wavelength interval of 518–527 nm corresponding to the region of the 4I15/2→2H11/2 transition was studied in detail at 293, 77, and 2 K. At 2 K, the spectrum of this transition displays six lines, which correspond to the theoretically possible number of sublevels of the 2H11/2 state of Er3+ ion occurring in a noncubic crystal field. The positions of levels in the 2H11/2 multiplet correspond to 2.360, 2.361, 2.365, 2.369, 2.379, and 2.386 eV. Both the number and narrow width of lines observed at 2 K indicate that Er3+ ions predominantly occupy the same regular position in GaN crystals. Most probably, erbium ions occupy gallium sites in the crystal lattice.

Temperature dependencies of excited states lifetimes and relaxation rates of 3–5 phonon (4–6 μm) transitions in the YAG, LuAG and YLF crystals doped with trivalent holmium, thulium, and erbium

Abstract The temperature dependencies of the nanosecond multiphonon relaxation (MR) rates of the 3 F 3 state of Tm3+ in the YLF crystal and of the 5 F 5 state of Ho3+ ion in the YAG and LuAG crystals and of the microsecond MR rates of the 4 F 9/2 ( 2 H 9/2 ) state of Er3+ ions in YLF were measured in the wide temperature range using direct laser excitation and selective fluorescence kinetics decay registration. For YLF the observed relations are explained by 4-phonon process in the frame of a single-frequency model with hω eff =450±30 cm −1 for the 3 F 3 state of Tm3+ and by 5-phonon process with hω eff =445 cm −1 for the 4 F 9/2 ( 2 H 9/2 ) state of Er3+. For YAG and LuAG crystals these dependencies are explained by the 3-phonon process with hω eff =630 cm −1 . The decrease of the relaxation rate with the temperature in the range from 13 to 80 K was observed for the 4 F 9/2 ( 2 H 9/2 ) state of Er3+ in the YLF crystal. It is explained by the redistribution of excited electronic states population of erbium ions over the higher lying Stark levels with different MR probabilities. A good fit of experimental temperature dependence (including the dropping part of the experimental curve) was obtained for single-frequency model ( hω eff =450 cm −1 ) with W 01 =8.0×10 4 s −1 and W 02 =4.7×10 4 s −1 accounting Boltzmann distribution of population over two excited Stark levels of the excited state of erbium ions. Employment of this model improves the fit between the experiment and the theory for the 5 F 5 state of Ho3+ ion in YAG as well. Strong influence of the parameters of the non-linear theory of MR, i.e. the reduced matrix elements U(k) of electronic transitions and the phonon factor of crystal matrix η on the spontaneous MR rates was observed experimentally. The smaller these parameters the slower the spontaneous MR W0. This fact can be used for searching new active crystal laser media for the mid-IR generation.

Site-selectivespectroscopy of Er3+ ions in the Bi12SiO20 piezoelectric crystal

Site-selective spectroscopy fluorescence experiments (emissionand excitation) in the near-infrared region associated with the4I15/2↔4I11/2 transitionsof Er3+ ions have been successfully used to show thepresence of two different Er3+ centres in theBi12SiO20 piezoelectric crystal. Green (545-570 nm),red (650-690 nm) and near-infrared (850-890 nm) up-converted emissions have been observed and resolved for each type ofcentre under excitation up to the 4I11/2 state. TheStark energy level schemes of the three lower energy states ofEr3+ ions have been determined and compared for bothcentres, showing two quite different crystalline fieldenvironments. The mechanisms responsible for the up-conversionprocess (excited state absorption and/or energy transfer up-conversion) are also analysed.

Intensities of optical transitions of Er3+ ions in a PbMoO4 crystal

On the basis of the analysis of absorption spectra of Er3+:PbMoO4 crystals made for the transitions from the ground 4I15/2 state to excited states of Er3+ ions by the Judd-Ofelt method, the main spectroscopic characteristics of the crystals were obtained, including the transition probabilities and the radiative lifetimes.

A STUDY ON ENERGY TRANSFER AND ENERGY MIGRATION MODELS FOR RE IONS LUMINESCENCE SYSTEM

By Application of the V-F-B model which is obtained by combining the Vasquez-Flint (V-F) model for donor-acceptor energy transfer and the model of Burshtein for donor-donor energy migration, the experimental luminescence decay curves of 4S3/2 state of Er3+ in LaF3 at 295K for four different concentrations are re-simulated successfully.It is found that in this system the donor-acceptor interaction is dipole-dipole interaction,and that the donor-acceptor interaction constant CDA is 4.75×10-41cm6/s. The results are all in agreement with the previous results of Okamoto. However, the hopping time τ0 obtained from the above simulation in proportional to xD-1.237 (xD is the donor concentration), which is different from the theoretical dependence on the donor concentration (that is τ0∝xD-2). In addition, by considering donor-acceptor energy transfer and donor-donor energy migration within the V-F model at the same time, we obtain the estimated values of the hopping time τ0′ for four different concentrations, which are in reasonable agreement with the values of τ0 obtained from the above simulation.It seems that the V-F-B model is rather self-consistent.

Comparison between the calculated and measured energy transfer rates of the S3/24 state in Er3+-doped fluorozirconate glasses

The dependence of the fluorescence lifetime of the S3/24 state of the Er3+ ion on the ErF3 concentration was measured in fluorozirconate glasses at room temperature. Energy transfer rates were calculated from optical parameters assuming that the Er3+ ions in fluorozirconate glasses were dispersed as the cubic, bcc, or fcc structure, and were inserted into the rate equation. The dependence of the total transition rate of the S3/24 state of the Er3+ ion on the ErF3 concentration was calculated by using the rate equation and compared with the total transition rate measured by the lifetime experiment. Although many studies have reported the energy transfer rates in various rare-earth ions, the reliability of the calculated energy transfer rates has been hardly discussed. The energy transfer rate can be derived from the total transition rate. The energy transfer rate estimated from the rate equation calculation was compared with the energy transfer rate obtained from the lifetime measurement. It could be shown that the calculated energy transfer rate assuming that the Er3+ ions were dispersed as the cubic structure was closer to the measured energy transfer rate than that as the bcc and fcc structures. With increasing the ErF3 concentration, the calculated energy transfer rate when the Er3+ ions were dispersed as the cubic structure was comparable to the measured energy transfer rate. It was suggested that at the lower concentration of ErF3 (⩽2 mol %), we needed to use the distance between Er3+ ions which was shorter than that as the cubic structure in the calculation of the energy transfer rate.

Resonant excitation of Er3+ by the energy transfer from Si nanocrystals

AbstractPhotoluminescence (PL) of SiO2 films co-doped with Si nanocrystals (nc-Si) and Er was studied. The average size of nc-Si was changed in a wide range in order to tune the exciton energy of nc-Si to the energy separations between the discrete electronic states of Er3+. PL from exciton recombination in nc-Si and the intra-4f shell transition of Er3+ were observed simultaneously. At low temperatures, periodic features were observed in the PL spectrum of nc-Si. The period agreed well with the optical phonon energy of Si. The appearance of the phonon structures implies that nc-Si which satisfy the energy conservation rule during the energy transfer process can resonantly excite Er3+. The effects of the quantum confinement of excitons in nc-Si on the energy transfer process are discussed.

Investigation of Coupling Mechanism between Erbium (Er3+) and Ytterbium (Yb3+) in Alumina (A12O3) Host

ABSTRACTPlasma-enhanced CVD (PECVD) deposited alumina (A12O3) thin films and single sapphire crystals were co-doped with both erbium and ytterbium using ion implantation. Yb3+ and Er3+ concentrations ranged from 2.4At% to 8At% and from 0.4At% to 0.8At%, respectively. The samples show relatively strong, broad, room-temperature photoluminescence (PL) at λ=11.53µm corresponding to the intra-4f transitions between the 4I13/2 (first excited) and the 4I15/2 (ground) state of Er3+. The full width at half maximum (FWHM) of the emission spectrum is as high as 67nm for the A12O3 thin films; for the sapphire crystals it is 45nm. The fluorescence lifetime of the samples has been measured to be as high as 4.2ms at 50mW laser pump power. The indirect pumping of erbium through the transfer of energy from ytterbium has been demonstrated and the PL peak intensity has been studied as a function of the Yb3+/Er3+ concentration ratio when the samples are pumped at 514nm and 850nm; the PL excitation spectrum (PL at 1.53gm as a function of pump wavelength) of an Er3+/Yb3+ co-implanted sample is also presented. Both the PL peak intensity at 1.53µm and the fluorescence lifetime have been studied as functions of annealing temperature. Luminescence spectra attributed to defects in the alumina matrix are presented for as-implanted samples and following thermal annealing.

Photoluminescence characterisation of Er3+/Yb3+ co-implanted alumina (Al2O3) thin films and sapphire crystals

Successful incorporation of both erbium and ytterbium in alumina by ion implantation is reported. Some evidence for indirect pumping of erbium through the transfer of energy from ytterbium has been observed. Both plasma-enhanced CVD deposited alumina thin films and sapphire crystals were employed as substrates. Yb3+ and Er3+ concentrations ranged from 2.4 At% to 8 At% and from 0.4 At% to 0.8 At%, respectively. The samples show strong, broad, room-temperature photoluminescence at λ = 1.53 µm corresponding to the intra-4f transitions between the 4I13/2 (first excited) and the 4I15/2 (ground) state of Er3+. The full width at half maximum of the emission spectrum is as high as 67 nm for the Al2O3 thin films; for the sapphire crystals it is 45 nm. The fluorescence lifetime of the samples has been measured to be as high as 4.2 ms at 50 mW pump power.

Fluorescence dynamics, excited-state absorption, and stimulated emission of Er^3+ in KY(WO_4)_2

The fluorescence dynamics from excited states of Er3+ in KY(WO4)2 are compared with Judd–Ofelt-theory calculations, and spectroscopic parameters of the promising laser transitions from the 4I13/2,4I11/2, and 4S3/2 levels are determined. The cw excited-state absorption spectra of Er3+-doped KY(WO4)2 are measured with a pump-and-probe technique and analyzed in the spectral range from 500 nm to 1800 nm. Energy transfer between Yb3+ and Er3+ ions in codoped KY(WO4)2 is investigated. Laser action near 1.54 μm under Ti:sapphire and diode-laser pumping is obtained in Er,Yb:KY(WO4)2.

Decay Kinetics from4I9/2State of Mixed 2,6 Pyridine Dicarboxylate-Acetylacetonate Complexes

Lanthanide ions are widely used as probes of their environment. The most useful ion in this respect is the Eu 3+ cation, because the emission generally occurs between a J = 0 state and the J = 0-6 levels of the ground state. The Tb 3+ cation is also useful but the high spherical degeneracies of the initial and terminal states greatly complicate tIe interpretation of the spectra. The 4F9/ 2 and 4I9/2 states of Er3+ are conspicuously long lived in high symmetry systems [1]. It was of interest to investigate whether emission from lower symmetry Er3+ complex ions could be detected and contained useful information.

Modulation of absorption and refractive index in Er3+-doped fibers

Abstract Modulation of the absorption and refractive index in Er3+-doped fibers for a signal wavelength in the 1550-nm band and a pump wavelength of 980 nm is investigated. The experimental results are compared with a model that takes into account optical transitions between the ground state and the metastable state in Er3+. Good agreement between the experiment and the model is obtained apart from a wavelength-independent constant in the refractive index modulation, which is discussed.

Ultraviolet emissions from Gd^3+ ions excited by energy transfer from pairs of photoexcited Er^3+ ions: upconversion luminescence from CsMgCl_3 crystals doped with Gd^3+ and Er3+

Crystals of CsMgCl3 containing Gd3+ and Er3+ exhibit UV emissions from excited Gd3+ ions when the 4S3/2(E) (546-nm) and the 2H11/2(F) (522-nm) states of Er3+ are pumped by pulsed laser excitation. The Gd3+ long-lived emissions that appear at 281 nm (τ = 6 ms) and 313 nm (τ = 3 ms) are assigned to the 6I7/2(C) and the 6P7/2(A) states, respectively. The luminescence dynamics indicate that the excited Gd3+ ions are produced by cooperative energy transfer from excited pairs of Er3+ ions. Direct excitation of the 4G9/2(T) state of Er3+ at 277 nm is shown to sensitize the Gd3+ emission at 281 nm. Excitation spectra that are observed when pumping the Er3+ states while monitoring the Gd3+ emissions indicate that there are spectroscopically distinct Er3+–Gd3+ clusters with slightly different absorption energies and noticeably different emission dynamics.

Effect of the Er3+ Concentration on the Luminescence of Ca1-xErxF2+x Thin Films Epitaxially Grown on Si(100)

AbstractCa1-xErxF2+x thin films, with a substitution rate, x, varying from 1 to 20%, were deposited on Si(100) substrates by sublimation of high purity solid solution powders under ultra-high-vacuum. Rutherford backscattering studies have shown that the films have the composition of the initial solid solution powders, are quite homogeneous and are epitaxially grown on the substrates.The optical properties of these films were studied by means of cathodoluminescence and photoluminescence. At room temperature, the emissions due to the de-excitations from the 4S3/2, 4F9/2, 4I11/2 and 4I13/2 excited levels to the 4I15/2 ground state of Er3+ (4f11) ions are easily detected (λ = 0.548, 0.66, 0.98 and 1.53 μm)The strong 1.53 μm infrared luminescence, which presents evident potential applications for optical communications, is maximum for an erbium substitution rate included between 15 and 17%. These Er concentrations are three or four orders of magnitude greater than the optimum ones in the case of Er-doped semiconductors, which are close to 1018 cm-3. In the visible range, the luminescences are also important.They allow us to detect high energy ion or electron beams. However their maximum efficiencies were observed for a relatively low erbium concentration, close to 1%. These different behaviours are explained by the cross relaxation phenomena, which depopulate the higher levels to the benefit of the 4I13/2 → 4I15/2 transition.The energy distribution of the Stark sublevels of the 4I15/2 state, which results from crystal field splitting, was deduced from a photoluminescence study at 2K. The obtained results show that the environment of the luminescent centres does not change with the erbium concentration.At last, it must be noted that the refractive index of the layers increases with the erbium concentration, leading to the realization of optical guides. Consequently opto-electronic components could be developed from such erbium doped heterostructures.

Energy transfer in Er 3+ /Pr 3+ -doped fluoride glass fibres and application to lasing at 2.7 μm

The influence of Pr3+ as a deactivating ion to shorten the lifetime of the 4I13/2 state of Er3+ is studied in fluoride glass (ZBLAN) fibres. The influence of clusters is shown to be of primary importance. Lasing performances of the Er3+4I11/2→4I13/2 transition at 2.7 μm with different Pr3+/Er3+ ratio are also reported.

Effects of energy transfer among Er^3+ ions on the fluorescence decay and lasing properties of heavily doped Er:Y_3Al_5O_12

Nonexponential fluorescence decay has been observed from both 4I11/2 and 4I13/2 states of Er3+ ions in heavily doped Er: YAG at room temperature. Processes of cross relaxation that originate in these states are shown to be responsible. Rate equations that include cross-relaxation processes are written and numerically solved, to result in the determination of the cross-relaxation coefficients. It is found that these coefficients do not change with Er3+ concentration. The effects of the cross-relaxation processes of Er3+ ions on fluorescence decay and lasing properties are discussed.

Experimental observation of the nonadditivity of various mechanisms of population inversion of the4I11/2→4I13/2transition of the Er3+ion in a YSGG:Cr3+:Er3+crystal

Experimental investigations were made of the threshold pump energy of a YSGG:Cr3+:Er3+ crystal as a function of the filtering wavelength of the pump radiation and the concentration of erbium ions. The contributions of two mechanisms of erbium ion excitation to population inversion of the 4I11/2 → 4I13/2 Er3+ transition in a YSGG:Cr3+:Er3+ crystal were nonadditive, as predicted previously. These mechanisms involved Cr→Er energy transfer and cross-relaxational depletion of the 4S3/2 state of Er3+.