Intrashell Transitions Research Articles

Photoluminescence and semiconductor properties of two novel lanthanide-mercury compounds with one-dimensional chain-like structures

Two novel lanthanide-mercury compounds [Ln(IA)3(H2O)2]n(Hg3Cl9)n·4nH2O (Ln = Eu (1) and Tb (2); IA = isonicotinic acid) have been synthesized under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction. Both complexes exhibit one-dimensional (1D) chain-like structure with a novel isolated (Hg3Cl9)3– anion. Solid-state diffuse reflectance spectroscopy reveals the presence of wide optical band gaps of 2.81 eV and 3.47 eV, suggesting that they are potentially wide band gap organic semiconductor materials. Solid-state photoluminescence measurements uncover that they show red or green light emission bands, respectively. The emission bands can be assigned to the characteristic emission of the 4f electrons intrashell transitions of 5D0 → 7FJ (Eu3+, J = 2 and 4) and 5D4 → 7FJ (Tb3+, J = 6, 5, 4 and 3), respectively. Energy transfer mechanism is explained by the energy level diagram of Eu3+ ion, Tb3+ ion and isonicotinic acid ligand. The title compounds have remarkable CIE chromaticity coordinates of (0.6438, 0.3559) and (0.3172, 0.4773). This suggests that they may be potential candidates with red or green light emitting materials for white light emitting diodes (LEDs).

Syntheses, structures, photoluminescence and semiconductor properties of two novel mercury-lanthanide complexes with a three-dimensional open framework

Two novel mercury-lanthanide complexes [Hg3Cl6(u-IA)3Ln(H2O)2]n (IA = isonicotinic acid anion; Ln = Pr (1) and Sm (2)) have been synthesized under hydrothermal conditions and structurally determined by single crystal X-ray diffraction. Complexes 1 and 2 are isostructure and feature a three-dimensional (3-D) open framework with two types of one-dimensional (1-D) chains. Based on the condensed 3-D open framework, there is a large void space being 1010.3 Å3 and 1018.1 Å3 which occupy 27.2% and 27.4% of the unit-cell volume for complexes 1 and 2, respectively. Solid-state UV/Vis diffuse reflectance spectroscopy reveals that there is a wide optical band gap of 3.51 eV and 3.54 eV for complexes 1 and 2, respectively. Photoluminescence measurements using solid-state samples discover that both complexes display red light emission. The emission bands can be ascribed to the characteristic emission of the 4f electron intrashell transitions of the Ln3+ ions, i.e. 1D2 → 3H4 and 3P0 → 3F3 transitions for complex 1, as well as 4G5/2 → 6H5/2, 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2 transitions for complex 2.

Electroluminescence color tuning between green and red from metal–oxide–semiconductor devices fabricated by spin-coating of rare-earth (terbium + europium) organic compounds on silicon

Color tunable electroluminescence (EL) from metal–oxide–semiconductor devices with the rare-earth elements Tb and Eu is reported. Organic compound liquid sources of (Tb + Ba) and Eu with various Eu/Tb ratios from 0.001 to 0.4 were spin-coated on an n+-Si substrate and annealed to form an oxide insulator layer. The EL spectra had only peaks corresponding to the intrashell Tb3+/Eu3+ transitions in the spectral range from green to red, and the intensity ratio of the peaks was appropriately tuned using the appropriate Eu/Tb ratios in liquid sources. Consequently, the EL emission colors linearly changed from yellowish green to yellowish orange and eventually to reddish orange on the CIE chromaticity diagram. The gate current +IG current also affected the EL colors for the medium-Eu/Tb-ratio device. The structure of the surface insulator films analyzed by cross-sectional transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS) has four layers, namely, (Tb4O7 + Eu2O3), [Tb4O7 + Eu2O3 + (Tb/Eu/Ba)SiOx], (Tb/Eu/Ba)SiOx, and SiOx-rich oxide. The EL mechanism proposed is that electrons injected from the Si substrate into the SiOx-rich oxide and Tb/Eu/Ba-silicate layers become hot electrons accelerated in a high electric field, and then these hot electrons excite Tb3+ and Eu3+ ions in the Tb4O7/Eu2O3 layers resulting in EL emission from Tb3+ and Eu3+ intrashell transitions.

Synthesis, second-harmonic generation (SHG), and photoluminescence (PL) properties of noncentrosymmetric bismuth selenite solid solutions, Bi2-xLnxSeO5 (Ln = La and Eu; x = 0–0.3)

A series of La3+ or Eu3+-doped noncentrosymmetric (NCS) bismuth selenite solid solutions, Bi2-xLnxSeO5 (x = 0.1, 0.2, and 0.3), have been successfully synthesized via standard solid-state reactions under vacuum with Bi2O3, La2O3 (or Eu2O3), and SeO2 as starting materials. Crystal structures and phase purities of the resultant materials were thoroughly characterized by powder X-ray diffraction using the Rietveld method. The results clearly show that the reported materials crystallize in the orthorhombic space group, Abm2 (No. 39), and exhibit pseudo-three-dimensional frameworks consisting of BiO3, BiO5, and SeO3 polyhedra that share edges and corners. Detailed diffraction studies indicate that the cell volume of Bi2-xLnxSeO5 decreases with an increasing amount of Ln3+ on the Bi3+ sites. However, no ordering between Ln3+ and Bi3+ was observed in the Bi2-xLnxSeO5 solid solutions. Powder second-harmonic generation (SHG) measurements, using 1064 nm radiation, reveal that SHG efficiencies of Bi2-xLnxSeO5 solid solutions continuously decrease as more Ln3+ cations are added to the sites of polarizable Bi3+ cations. Photoluminescence (PL) measurements on Bi2-xEuxSeO5 exhibit three specific emission peaks at 592, 613, and 702 nm (5D0 → 7F1, 2, 4) owing to the 4f-4f intrashell transitions of Eu3+ ions.

Rapid solution combustion synthesis of sponge like mesoporous Ce3+ doped yttrium aluminium oxide

We present here an effective and facile method to synthesize hierarchical sponge-like mesoporous trivalent cerium (Ce3+) doped cubic (YAG (Y3A5O12)) and monoclinic (YAM (Y4A2O9)) yttrium aluminium oxide (YAlO) by a single step self propagating low temperature combustion technique without any post heating. The X-ray diffraction study revealed the formation of YAG and YAM structures and optimum incorporation of dopant is confirmed through precipitated secondary phase at higher Ce3+ concentration. Raman spectra of undoped and Ce3+ doped YAlO shows the characteristics peaks of YAG and YAM structure. The field emission scanning electron micro graphs (FESEM) reveal highly porous sponge-like surface with individual pore size of about 12–15 nm. The photoluminescence studies show efficient single band emission spectra centered at 568 and 550 nm for Ce3+ doped YAG and YAM respectively due to intra-shell transitions of the rare earth atom, compared to negligible emission in visible region for undoped YAlO due to defects present in the host lattice. Influence of dopant and the changes observed in structural, morphological and luminescence studies due to differences in crystal field environment (cubic and monoclinic) are explained in detail. Such highly stable mesoporous material with luminescence in visible region is suited for applications in illumination devices like white LEDs for indoor and outdoor lighting and also high end biomedical applications such as tumor targeting.

Characteristics of thulium doped gallium oxide films grown by pulsed laser deposition

Thulium (Tm) doped Ga2O3 films were deposited on sapphire substrates by pulsed laser deposition (PLD) with changing Tm compositions in the targets. Energy dispersive spectroscopy results reveal that films with different Tm compositions can be tailored by changing the Tm composition in the targets. X-ray diffraction and Raman spectra analysis indicate that all films have the monoclinic structure. Photoluminescence measurements demonstrate that the emission peaks at 460, 650 and 800nm are observed from the Tm3+ 4f intrashell transitions from 1G4 excited states to the 3H6, 3F4, and 3H5 states, respectively. The results suggest that PLD is a promising method for obtaining high quality Tm doped Ga2O3 films, which paves the way for the fabrication of optoelectronic devices based on Ga2O3 films.

Surface localization of the Er-related optical active centers in Er doped zinc oxide films

Er-doped ZnO films were grown on c-plane sapphire by employing the pulsed laser deposition method. In accordance with the previously reported literature studies, post-growth annealing was required to activate the optical emission originated from the intra-shell transitions of the Er atoms. Importantly, the present systematic studies revealed that the thermal activation of the optical activity is due to the atomistic rearrangements occurring only in the vicinity of the film surface. The processes exhibit a distinct signature of changing oxygen coordination with the Er atom, as observed by the x-ray photoemission study.

Photoluminescence and structure of sputter-deposited Zn2SiO4:Mn thin films

Mn-doped Zn2SiO4 thin films were deposited on Si (100) substrates by radio-frequency (RF) magnetron sputtering. The deposited films were then annealed at temperatures ranging from 600 to 1200 °C in an air ambient for 1 hour. The as-deposited Zn2SiO4:Mn films exhibited an amorphous structure having a smooth surface and showed no photoluminescence (PL). Annealing at 600 °C was found to have little effect on the properties of the films. The films still remained amorphous with no PL. After annealing at 800 °C, the films were crystallized in a mixture of orthorhombic β-Zn2SiO4 and rhombohedral α-Zn2SiO4 phases. These films showed a PL emission spectrum that could be resolved into two bands, one centered at 520 nm in the green region and the other at 571 nm in the yellow region. The green PL emission originated from the 4T1 → 6A1 intrashell transition of Mn2+ ions in the α-Zn2SiO4 phase while the yellow emission was attributed to Mn2+ ions in β-Zn2SiO4. The films annealed at and above a temperature of 900 °C exhibited only the α-Zn2SiO4 phase, and the PL spectra of these films showed only the green emission band with a peak maximum at around 523 nm. The PL emission intensity increased with increasing annealing temperature, which was due to the better crystalline quality and the rougher surface morphology of the Zn2SiO4:Mn films annealed at higher temperatures.

Structural, diffused reflectance and photoluminescence study of cerium doped ZnO nanoparticles synthesized through simple sol–gel method

Cerium ion doped ZnO (ZnO:Ce3+) nanomaterials were successfully synthesized via inexpensive sol–gel method. The effect of Ce ion doping on the structural and optical properties of ZnO nanoparticles were investigated in detail. Crystallography and morphology were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). X ray diffraction results revealed that increasing cerium concentration from 0.3 to 1.0mol%, a gradual increment in lattice parameters followed by the reduction in average crystallite size from 20nm to 16nm was observed. The XRD patterns demonstrate that the ZnO nanoparticles are highly crystalline and cerium ions were successfully incorporated into the lattice position of ZnO. Formation of ZnO:Ce3+ nanoparticles were observed from the transmission electron microscopy. Furthermore, optical absorption and photoluminescence (PL) spectroscopy measurements confirm this finding. Optical band gap energy of undoped ZnO was ∼3.18eV which decreased to 3.14eV by introducing cerium ion (0.3mol%), moreover, the band gap reduced to 3.13eV as a result of increasing cerium concentration up to 1.0mol% which leads to the formation of various optically active sub-levels. Photoluminescence spectroscopic results revealed that UV emission originated from near-band-edge transitions. The shift in the near-band-edge emissions towards lower wavelength attributed to the change in the carrier concentration or strain induced by doping. The intense band ∼545nm and 564nm for ZnO:Ce1.0mol% may be due to charge transfer of ZnO lattice to the cerium ion. The band ∼613 (2.02eV) nm may be due to 4f–4f intra-shell transition 5D0→7F2 confirms the incorporation of Ce3+ in to wurtzite ZnO host by substitution on the Zn sub lattice.

Facile combustion synthesized orthorhombic GdAlO3:Eu3+ nanophosphors: Structural and photoluminescence properties for WLEDs

Nanoparticles of Eu3+ doped (1–11mol%) GdAlO3 were prepared using low temperature (350°C) solution combustion technique with gadalonium nitrate as oxidizer and oxalyl di-hydrazide (ODH) as a fuel. The synthesized samples were calcined at 1000°C for 3h and used for Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and UV–visible absorption (UV–vis) characterization techniques. A pure orthorhombic was obtained in calcined samples. The average crystallite sizes were estimated using Scherrer's formula, W–H and size–strain plots and found to be in the range 25–50nm and the same was confirmed by Transmission electron microscopy (TEM) studies. The phosphors exhibit bright red emission upon 395nm excitation. The characteristic emission peaks recorded at ~591, 612, 654 and 694nm (5D0→7Fj=1,2,3,4) were attributed to the 4f–4f intra-shell transitions of Eu3+ ions. The CIE chromaticity co-ordinates were calculated from emission spectra, the values (x, y) were very close to NTSC standard value of red emission. Further, the average CCT value was found to be ~2369K, as a result the prepared nanophosphor was highly useful for red component of white light emitting devices and also for solid state display applications.

Ray-tracing simulations of spherical Johann diffraction spectrometer for in-beam X-ray experiments

The results of the Monte-Carlo ray-tracing simulations for a Johann-type Bragg spectrometer with spherically curved-crystal designed to detect the X-rays from a fast-moving source are reported. These calculations were performed to optimize the X-ray spectrometer to be used at the gas-target installed at ion storage ring for high-resolution X-ray experiments. In particular, the two-dimensional distributions of detected photons were studied using the Monte-Carlo method both for the stationary and moving X-ray sources, taking into account a detailed description of X-ray source and X-ray diffraction on the crystal as well as a role of the Doppler effect for in-beam experiments. The origin of the asymmetry of observed X-ray profiles was discussed in detail and the procedure to derive a precise (sub-eV) X-ray transition energy for such asymmetric profiles was proposed. The results are important for the investigations of 1s2pP23→1s2sS13 intrashell transition in excited He-like uranium ions in in-beam X-ray experiments.

Ultraviolet and white electroluminescence from metal–oxide–semiconductor devices fabricated by spin-coating of gadolinium organic compounds on silicon

Ultraviolet (UV) and white electroluminescence (EL) from metal–oxide–semiconductor (MOS) devices with indium–tin oxide (ITO)/[(Gd/(Gd + Dy/La/Ca/Ba)–Si–O] insulator layers/n+-Si substrate are reported. The insulator layers were fabricated from mixtures of organic liquid sources of (Gd) or [Gd+(Dy/La/Ca/Ba)], which were spin-coated on the n+-Si substrate and annealed at 950 °C for 30 min in air. The current IG under EL emission corresponded to the Fowler–Nordheim (FN) tunnel current. The EL intensity increased proportionally to IG to the n-th power, where n was about 1.2, and the EL spectra were independent of IG. The MOS device with the [(Gd + Dy)–Si–O] layer had the weakest EL in the UV range among the measured devices, while it had the strongest EL in the visible wavelength range. The UV and visible range EL originated from the intrashell transitions of 6P7/2–8S7/2 in Gd3+ and 4F9/2–6HJ/2 (J = 9, 11, 13, and 15) in Dy3+, respectively. The devices with [(Gd/(Gd + La/Ca/Ba)–Si–O] layers emitted strong UV EL, which originated from the intrashell transitions of 6P7/2–8S7/2 in Gd3+, and had the moderate intensity of EL in the visible range. The insulator layers of EL devices had a thickness of 25–30 nm and the double layer structure, whose top surface layer contained [Gd2O3+DyOx+(Gd + Dy)–Si–O]/[Gd2O3+La2O3/CaO/BaO+(Gd + La/Ca/Ba)–Si–O] silicate, while the underlayer was composed of SiOx-rich oxide with various rare earth and alkaline earth oxides.

Interference effects and Stark broadening in XUV intrashell transitions in aluminum under conditions of intense XUV free-electron-laser irradiation

Quantum mechanical interference effects in the line broadening of intrashell transitions are investigated for dense plasma conditions. Simulations that involved $LSJ$-split level structure and intermediate coupling discovered unexpected strong line narrowing for intrashell transitions $L$-$L$ while $M$-$L$ transitions remained practically unaffected by interference effects. This behavior allows a robust study of line narrowing in dense plasmas. Simulations are carried out for XUV transitions of aluminum that have recently been observed in experiments with the FLASH free-electron laser in Hamburg irradiating solid aluminum samples with intensities greater than ${10}^{16}$ W/cm${}^{2}$. We explore the advantageous case of Al that allows, first, simultaneous observation of $M$-$L$ transitions and $L$-$L$ intrashell transitions with high-resolution grating spectrometers and, second, has a convenient threshold to study interference effects at densities much below solid. Finally, we present simulations at near solid density where the line emission transforms into a quasicontinuum.

Evidence of multicenter structure of cerium ions in gadolinium gallium garnet crystals studied by infrared absorption spectroscopy

Low temperature, infrared absorption spectra of gadolinium gallium garnet crystals doped with Ce are presented. In the region of intraconfigurational 4$f$-4$f$ transitions the spectra exhibit existence of at least two different, major Ce${}^{3+}$ related centers in the GGG crystals and also some other centers at lower concentration. The spectrum of 4$f$-4$f$ intrashell transitions of Ce${}^{3+}$ ions extends up to about 3700 cm${}^{\ensuremath{-}1}$ due to the large splitting of the ${}^{2}$${F}_{7/2}$ excited state. In the visible region the absorption spectrum shows influence of symmetry-related selection rules. The absorption coefficient changes in the region of 4${f}^{1}$-5${d}^{1}$ transitions due to thermal population of the second level, belonging to the ${}^{2}$${F}_{5/2}$ ground state. This suggests that the symmetry of the site occupied by Ce${}^{3+}$ ions, which substitute Gd${}^{3+}$, is higher than ${D}_{2}$ expected for garnet hosts.

Optical and magnetic properties of ZnCoO layers

Optical and magneto-optical properties of ZnCoO films grown at low temperature by Atomic Layer Deposition are discussed. Strong wide band absorption, with onset at about 2.4eV, is observed in ZnCoO in addition to Co-related intra-shell transitions. This absorption band is related to Co 2+ to 3+ photo-ionization transition. A strong photoluminescence (PL) quenching is observed, which we relate to Co recharging in ZnO lattice. Mechanisms of PL quenching are discussed.

Unidentified transitions in one-photon intrashell dynamics in Rydberg atoms

One-photon intrashell transitions in strongly driven Li ($n=25$) atoms are studied experimentally. The degeneracy of the $n$ shell is lifted by orthogonal dc electric and magnetic fields, which also define the eccentricity of the initial coherent elliptic state. The transitions are driven by a radio frequency pulse linearly polarized parallel to the major axis of the ellipse. A small dc electric field component parallel to the magnetic field splits the one-photon resonance into two, and transitions in between are studied by state-selective field ionization. Unexpected lines in the ionization spectra relating to unknown transitions are found and discussed.

Effects of mineralizing agent on the morphologies and photoluminescence properties of Eu 3+-doped ZnO nanomaterials

Eu-doped ZnO nanomaterials with different morphologies were successfully synthesized with various mineralizing agents by the mild hydrothermal method. The mineralizing agent was found to have strong effect on the crystal structures, morphologies and photoluminescence properties of the samples. Transmission electron microscopy and scanning electron microscopy images showed the Eu-doped ZnO nanorods, nanoneedles and cactus-like microspheres based on nanosheets can be fabricated by choosing NaOH, C 6H 12N 4 and (NH 2) 2CO as the mineralizing agents, respectively. The results from X-ray diffraction and X-ray photoelectron spectroscopy indicated europium ions with trivalent valence were successfully doped into the crystal lattice of ZnO matrix. In the PL spectra from the Eu-doped ZnO nanomaterials synthesized with mineralizing agents of NaOH or (NH 2) 2CO, three separated red emissions can be obviously observed, which can be attributed to the 4f–4f intrashell transitions of 5D 0 → 7F 0, 5D 0 → 7F 1 and 5D 0 → 7F 2 of Eu 3+ ions, respectively. The intensity of red emission was found to be related with the concentration of intrinsic defects, especially O-vacancies, which could assist the energy transfer from the ZnO host to the Eu 3+ ions.

Suppression of multiphoton intrashell resonances in Li Rydberg atoms

Multiphoton intrashell transitions in strongly driven Li ($n=25$) Rydberg atoms are studied experimentally. Orthogonal dc electric and magnetic fields lift the degeneracy of the $n$ shell and define the eccentricity $e$ of the initial coherent elliptic states, which are formed by laser excitation and subsequent adiabatic transformation. The intrashell transitions are driven by a time-harmonic electric field linearly polarized parallel to the major axis of the ellipse. $N$-photon resonances with $N=1\ensuremath{-}9$ are studied as a function of $e$. All resonances with $N\ensuremath{\geqslant}3$ are suppressed at certain $e$ values in between $0$ and $1$. A similar system was analyzed by Yabuzaki et al. [Phys. Rev. A 10, 1955 (1974)] who found a simple pattern of suppressions that applies also for the present experiments. The results of these experimentally confirm that each time $N$ is increased by two, an additional suppression is observed.

Differential energy measurement between He- and Li-like uranium intra-shell transitions

We present the first clear identification and highly accurate measurement of the intra-shell transition 1s2p 3P2→1s2s 3S1 of He-like uranium performed via x-ray spectroscopy. The present experiment was conducted at the gas-jet target of the ESR storage ring in GSI (Darmstadt, Germany), where a Bragg spectrometer, with a bent germanium crystal, and a Ge(i) detector were mounted. Using the ESR deceleration capabilities, we performed a differential measurement between the 1s2p 3P2→1s2s 3S1 He-like U transition energy, at 4510 eV, and the 1s22p 2P3/2→1s22s 2S1/2 Li-like U transition energy, at 4460 eV. By a proper choice of the ion velocities, the x-ray energies from the He- and Li-like ions could be measured, in the laboratory frame, at the same photon energy. This allowed for a drastic reduction of experimental systematic uncertainties, principally due to the Doppler effect, and for a comparison with theory without the uncertainties arising from one-photon quantum electrodynamics predictions and nuclear size corrections.

Green/Red Electroluminescence from Metal–Oxide–Semiconductor Devices Fabricated by Spin-Coating of Rare-Earth Organic Compounds on Silicon

Current–voltage (IG–VG) characteristics and green/red electroluminescence (EL) from metal–oxide–semiconductor (MOS) devices with indium–tin oxide (ITO)/[(Tb/Ba–Si–O)/(Tb/Eu–Si–O)] layers/n+-Si substrate are reported. The (Tb/Ba–Si–O) and (Tb/Eu–Si–O) layers were fabricated from the mixtures of organic liquid sources of (Tb+Ba) and (Tb+Eu), respectively, which were spin-coated on the n+-Si substrate and annealed at 850 °C for 30 min in air. IG currents under EL emission correspond to Fowler–Nordheim (FN) tunnel current. The MOS devices with the (Tb/Ba)–Si–O layer and the (Tb/Eu)–Si–O layer emitted green and red EL, which originated from the intrashell transitions of 5D4–7FJ (J = 6, 5, 4, and 3) of Tb3+ ions and 5D0–7FJ (J = 1, 2, 3, and 4) of Eu3+ ions, respectively. EL intensity increased proportionally to IG to the n-th power, where n was about 1.3, and the EL spectra were independent of the currents. The oxide layers on the Si substrate for the green and the red devices have the total thicknesses of about 40 and 30 nm, which consist of [Tb2O3 and (Tb/Ba–Si–O)] and [Tb2O3/Eu2O3 and (Tb/Eu–Si–O)] mixtures, respectively.