Er Impurities Research Articles

Optical polarizability of erbium-oxygen complexes in sol-gel-based silica films

For erbium (Er)-doped amorphous oxides, such as those that are used in compact lightwave devices interfaced with silicon, values of the refractive indices are commonly obtained empirically. This work, combining experimental and theoretical studies, examines silica as the exemplary host and the influence of Er doping on the refractive index. Analysis of data is presented for the spectral refractive index in the ultraviolet to near infrared wavelength range of heavily Er-doped silica thin films prepared by spin coating a sol-gel precursor on silicon and subsequent vacuum annealing. Effective medium Lorentz–Lorenz data analysis determines that the dopant component has a refractive index of 1.76 ± 0.24 with wavelength dispersion constrained to within 2%. Considering the dopant as a localized ErO6 impurity complex, a corresponding theoretical refractive index of 1.662 is derived by calculating the optical polarizability and volume of the impurity. Data presented for room-temperature (∼293 K) photoluminescence in the vicinity of 1.54 μm are shown to be consistent with random variability in impurity sites. Inherent advantages of studying colloid-based materials are discussed. To the best of the authors’ knowledge, such a detailed study of the refractive index associated with Er impurities in silica is being reported for the first time in the literature.

Detection of Two Phenomena Opposite to the Expected Ones

Both phenomena mentioned in the title were revealed by the electron paramagnetic resonance (EPR) method. The first phenomenon was found in superconducting La metal with Er impurities—the spin relaxation rate of the erbium impurities was sharply decreasing after transition into the superconducting state instead of the expected, i.e., the well-known Hebel–Slichter peak. The second unexpected phenomenon was discovered in the YbRh2Si2 compound—an excellent EPR signal from the Yb ions was observed at temperatures below the Kondo temperature determined thermodynamically, while according to the existing belief the EPR signal should not be observed at these temperatures due to the Kondo effect. In this tribute to K. Alex Müller, I describe the nature of the detected phenomena.

27a-N-12 GaAs中のErと複合欠陥

27a-N-12 GaAs中のErと複合欠陥

Effect of potassium and erbium co-doping on the structural, electronic, optical and magnetic properties of zinc oxide

Electronic and optical properties of (K, Er) co-doped ZnO were investigated by using FP-LAPW method with LSDA and LSDA+mBJ approximations. The lattice parameter of undoped ZnO was found in a good agreement with the experimental work; it was increased by doping ZnO with K and Er impurities. In this work, we showed the p-type doping ZnO from the band structure and density of states calculations. The band gap of ZnO was found to be decreased by co-doping with K and Er elements. We presented also the optical properties such as, the real and imaginary part of dielectric function, the refractive index and the absorption coefficient. This p-type appears by K and Er co-doping which occurs much shallow above the Fermi level. Er co-doping leads to the formation of magnetism in ZnO:K. ZnO has an absorption peak in UV region. Hence, (K, Er) co-doping leads to an optical peak in infrared region (IR) at about 1.75eV (equivalent to 775nm). The peak was found experimentally, and may improve the optical properties of ZnO-based devices.

Spectroscopy of the Er-doped lithium tetraborate glasses

The electron paramagnetic resonance (EPR), optical absorption, and luminescence (emission and excitation) spectra as well as luminescence kinetics of the Er-doped glasses with Li2B4O7 composition were investigated and analysed. The high optical quality glasses with Li2B4O7:Er composition containing 0.5 and 1.0mol.% Er2O3 were obtained from corresponding polycrystalline compound by standard glass synthesis. The EPR spectroscopy in the 4.2–300K temperature range and optical spectroscopy at 300K show that the Er impurity is incorporated into the network of Li2B4O7 glass as Er3+ (4f11, 4I15/2) ions, exclusively. The local structure of the Er3+ luminescence centres in Li sites of the glass network is proposed. Based on the standard Judd–Ofelt theory the oscillator strength (Pcal) and experimental oscillator strength (Pexp) for observed absorption transitions as well as phenomenological intensity parameters (Ω2, Ω4, Ω6) for Er3+ centres in the Li2B4O7:Er glass containing 1.0mol.% Er2O3 were calculated. Spectroscopic parameters of relevance for laser applications, including emission probabilities of transitions (Wr), branching ratios (β), and radiative lifetime (τrad) have been calculated for main observed emission transitions of the Er3+ centres in Li2B4O7:Er glasses. Experimental and calculated lifetimes were compared and quantum efficiency (η) for green (4S3/2→4I15/2 transition) and infrared (4I13/2→4I15/2 transition) emission bands has been estimated.

Hybrid density functional study of optically active Er3+ centers in GaN

Understanding the luminescence of GaN doped with erbium (Er) requires a detailed knowledge of the interaction between the rare-earth dopant and the nitride host, including intrinsic defects and other impurities that may be present in the host material. We address this problem through a first-principles hybrid density functional study of the structure, energetics, and transition levels of the Er impurity and its complexes with N and Ga vacancies, substitutional C and O impurities, and H interstitials in wurtzite GaN. We find that, in the interior of the material, Er$_{\rm Ga}$ is the dominant Er$^{3+}$ center with a formation energy of 1.55 eV; Er$_{\rm Ga}$-$V_{\rm N}$ possesses a deep donor level at 0.61 eV which can assist in the transfer of energy to the 4$f$-electron core. Multiple optically active Er$^{3+}$ centers are possible in Er-doped GaN.

Effect of ion irradiation on the structure and luminescence characteristics of porous silicon impregnated with tungsten-telluride glass doped by Er and Yb impurities

Using transmission electron microscopy and elemental analysis, it has been shown that tungsten telluride glass (TTG) containing erbium and ytterbium as impurities penetrates into pores of porous silicon (PS) when melted in vacuum at 500°C. It has been found that the intensity of photoluminescence (PL) of erbium at the wavelength of 1.54 μm in PS: TTG layers increases by a factor of up to 5 in the layers irradiated by P+ and Ar+ ions. This is assigned to ion mixing which favors interaction among the Er ions and PS-embedded Si nanocrystals initiating sensitization of the PL, as well as to broadening of the glass-impregnated PS region. Implantation of the lighter Ne+ ions affects only weakly the PL of erbium ions.

The processes of erbium impurity excitation in Si/Si1−xGex:Er/Si heteroepitaxial structures

We report a study into the photoluminescence excitation spectra of Er3+ ions in Si/Si1−xGex:Er/Si heteroepitaxial structures containing 10–31% germanium. The structures of this type are of interest for a laser realization on Si basis. It is shown that a characteristic maximum in the 1040–1050nm region that appears in these structures is related with the backscattering effects of radiation in the silicon substrate. The excitation efficiency of Er impurity in Si/Si1−xGex:Er/Si structures is investigated in conditions of band-to-band and sub-bandgap optical pumping with the photon energies smaller than the bandgap of a Si1−xGex solid solution. The effective excitation cross-section of erbium ions is shown to depend on the excitation mechanism, the excitation energy, and the parameters of Si1−xGex:Er layers. The values of the effective excitation cross-section of Er3+ ions in Si/Si1−xGex:Er/Si structures were found to vary from 4×10−15 to 0.5×10−16cm2 at T=77K. These values are comparable with the highest values obtained for the excitation cross-section of Er3+ ions in silicon and exceed by several orders of magnitude the effective cross-section of Er3+ ions under direct (intra-atomic) excitation.

Photoinduced Current Transient Spectroscopy of TlInS2Layered Crystals Doped with Er, B, and Tb Impurities

Photoinduced Current Transient Spectroscopy of TlInS₂Layered Crystals Doped with Er, B, and Tb Impurities

Dependence of the concentration of ionized donors on epitaxy temperature for Si:Er/Si layers grown by sublimation molecular-beam epitaxy

The dependence of the concentrations of the Er impurity and ionized donors on the epitaxy temperature has been studied before and after annealing of Si:Er/Si layers grown by sublimation molecular-beam epitaxy. n-Si:Er layers have been grown in the temperature range 400–800°C and annealed in hydrogen atmosphere at a temperature of 800°C for 30 min. The possible nature of the donor centers is discussed.

Electrical Charge Transfer in Complex Oxides

In this paper, it is considered the experimental data of study of crystals with dierent structure types, from the point of view of behaviour of electrically active structural defects in complex oxides under the external electrical field. The electronic part of electrical transfer is investigated. The features of electric and dielectric properties caused partly by complex point defects and their temperature behaviour in Ca3Ga2Ge3O12 and Ca3Ga2Ge4O14 single crystals (with the garnet (CGGG) and Ca-gallogermanate (CGG) structure, respectively), and in AWO4:PbWO4 (PbWO), CaWO4 (CaWO), and CdWO4 (CdWO) (with the sheelite and volframite structure, respectively) are also considered. In this work, main emphasis is paid to investigation of undoped crystals. In the case of CGGG measurements were carried out also for the crystals containing the introduced Cr, Mn, Co, Nd, Er impurities. The mentioned oxides are well-known compounds as

Spatial distribution of defects and the kinetics of nonequilibrium charge carriers in GaN wurtzite crystals doped with Sm, Eu, Er, Tm, and supplementary Zn impurities

By analyzing time-resolved and steady-state photoluminescence spectra, it is established that the spatial distribution of rare-earth ion dopants in wurtzite GaN crystals doped with Sm, Eu, Er, or Tm is governed by the type and concentration of defects in the initial semiconductor matrix as well as by the type of the impurity (its capacity for segregation). Doping with multicharged rare-earth impurities and additionally introduced Zn impurity leads to an intensification of emission. The effect of intensification of emission in the case of n-and p-GaN crystals is considered with the use of the model of isoelectronic traps.

EPR and optical measurements of weakly doped LiNbO 3: Er

Optical spectroscopy measurements of the congruent LiNbO 3 (LN) single crystals, weakly doped with Er (0.1–0.3 wt%) and Er (0.3 wt%) and Yb (0.5 wt%), have been carried out. The shape of the optical absorption and additional absorption bands registered after γ-irradiation suggests the presence of Er 3+ ion pairs. EPR investigations were performed for LN single crystal doped with Er (0.1 wt%). Unusual behaviour of the temperature dependence of the intensity and linewidth of the main EPR line—corresponding to the fine transition of evenEr 3+—ions, is reported. The main EPR line appears to be a superposition of several paramagnetic centres originating from isolated evenEr 3+ ions and evenEr 3+– evenEr 3+ pairs of ions. In low temperature region (below 20 K), the main EPR signal is dominated by signals arising from evenEr 3+– evenEr 3+ pairs of ions. The inverse intensity of the EPR line at low temperature region fulfils the Curie–Weiss law and enabled to determine the Curie–Weiss constant Θ=1.5±0.5 K. The positive sign of Θ suggests that the ferromagnetic interactions arise in the system of evenEr 3+– evenEr 3+ ion pairs in LN. Our results suggest that the distribution of Er ions in congruent LN is not homogeneous and Er impurity ions can form clusters in host lattice even in the case of weak erbium doping.

Monitoring delamination of plasma-sprayed thermal barrier coatings by reflectance-enhanced luminescence

Plasma-sprayed thermal barrier coatings (TBCs) present a challenge for optical diagnostic methods to monitor TBC delamination, because the strong scattering exhibited by plasma-sprayed TBCs severely attenuates light transmitted through the TBC. This paper presents a new approach that indicates delamination in plasma-sprayed TBCs by utilizing a luminescent sublayer that produces significantly greater luminescence intensity from delaminated regions of the TBC. Freestanding coatings were produced with either a Eu-doped or Er-doped yttria-stabilized zirconia (YSZ) luminescent layer below a plasma-sprayed undoped YSZ layer. A NiCr backing layer was added to represent an attached substrate in some sections. For specimens with a Eu-doped YSZ luminescent sublayer, luminescence intensity maps showed excellent contrast between unbacked and NiCr-backed sections. Discernable contrast between unbacked and NiCr-backed sections was not observed for specimens with a Er-doped YSZ luminescent sublayer, because luminescence from Er impurities in the undoped YSZ layer overwhelmed luminescence originating from the Er-doped YSZ sublayer.

Hydrogenation effect on enhancement of photoluminescence of Er and Si nanocrystallites in Er-doped SiO2 synthesized by laser ablation

Significant enhancement of photoluminescence (PL) was attained for Er ions and Si nanocrystallites (nc-Si) in SiO2 films by two kinds of hydrogenation, using H2 molecules or H atoms. Er-doped SiO2 films containing Er impurities and a high density of nc-Si were fabricated by laser ablation of Er films deposited on Si substrate in an O2 gas atmosphere, followed by annealing at high temperatures in flowing Ar gas. Hydrogenation at 300–500 °C was found to effectively increase the PL intensity of Er ions as well as that of nc-Si. In particular, the hydrogen atom treatment dramatically shortens the hydrogenation time for the enhancement of Er PL compared to the hydrogen molecule treatment. Spectra of electron spin resonance showed a decrease in residual defects, namely, Pb-type defects located at the interfaces between nc-Si and SiO2 by hydrogenation. These results clearly show the effectiveness of hydrogen passivation for Si nanostructures; i.e., the increase in the Er PL and nc-Si PL due to hydrogen passivation of the nonradiative recombination centers located at the interfaces between nc-Si and SiO2.

Laser and Properties of Nanostructured Materials

We review optical and electronic properties of Si-based nanostructured materials, such as O-dimensional Si nanocrystallites with sizes from 1 nm to 10 nm and 1-dimensional Si nanowires, that are synthesized using laser ablation techniques. Characteristics of clusters consisting of several atoms to hundreds of atoms are also described in order to understand the physical and chemical properties of Si-based nanostructured materials. Si nanocrystallites with sizes below 5 nm widen band gaps arising from the quantum confinement effect. P and Er impurities exhibit novel properties in SiO2 matrices including Si nanocrystallites. Si nanowire can be grown via vapor-liquid-solid mechanism. Quantized conductance and Coulomb blockade are described for the nanowires having interesting quantum properties.

Impurity centers of rare-earth ions (Eu, Sm, Er) in GaN wurtzite crystals

Gallium nitride (GaN) was doped with Eu, Sm, and Er impurities using the diffusion method. The behavior of rare-earth impurities (the formation of donor or acceptor levels in the GaN band gap) correlates with the total concentration of defects, which is determined from optical measurements, and with the position of the Fermi level in starting and doped crystals. The intensity of emission lines, which are characteristic of the intracenter f-f transition of rare-earth ions, is controlled by the total defect concentration in the starting semiconductor matrix.

Optically active erbium–oxygen complexes in GaAs

Density functional modeling of Er and Er–O complexes in GaAs show that Er impurities at the Ga site are not efficient channels for exciton recombination, but decorative O atoms play crucial roles in inhibiting Er precipitation and in creating the necessary conditions for electron-hole capture. Among the defects studied, the ErGaOAs and ErGa(OAs)2 models have the symmetry and carrier trap location close to the defect responsible for the strong 1.54 μm photoluminescence band in Er, O codoped GaAs.

Photoluminescence of AgGaS 2 and CuGaS 2 doped with rare-earth impurities

Photoluminescence (PL) related to rare-earth (RE) impurities (Ho, Er and Eu) in AgGaS 2 and CuGaS 2 crystals has been studied. In Ho-doped AgGaS 2 and CuGaS 2, two series of PL lines are observed in 1.86–1.92 eV region and 2.24 eV region, and they are assigned to 5F 3– 5I 7 and 5S 2– 5I 8 transitions of the Ho 3+ ion, respectively. Similarly, in Er-doped AgGaS 2 and CuGaS 2, Er 3+-related two PL series are observed: 1.83–1.88 eV region ( 4F 9/2– 4I 15/2) and 2.22–2.26 eV region ( 4S 3/2– 4I 15/2). For both Ho and Er impurities, the profile of the PL spectrum in AgGaS 2 is complex, and PL exhibited large number of lines compared with that in CuGaS 2. The differences in PL spectra between this two compounds are related to the crystal field at the cation site and the local atomic arrangement of the RE impurities. This work also refers to the PL band at 2.28 eV observed for the Eu-doped AgGaS 2 crystal.

Electronic structure of light emitting centers in Er doped Si

Ab-initio calculations are carried out for the Er-related electrically active centers in Si. Our proposed microscopic model is consistent with photoluminescence measurements on Si:Er and Si:Er:O samples. For isolated Er, the tetrahedral interstitial site is the stable configuration, being related to the photoluminescence lines in Si:Er. Several configurations containing oxygen and fluorine atoms, surrounding the Er impurities, are proposed to simulate the effects of co-implantation. The results suggest that six oxygen atoms around substitutional Er can stabilize the center, which can be related to the strong photoluminescence lines in Si:Er:O samples. On the other hand, no configuration containing fluorine atoms could explain the stronger photoluminescence lines resulting from fluorine co-implantation.