Eu Thin Films Research Articles

A research on growth and characterization of CdS:Eu thin films

Chemical spray pyrolysis-grown CdS thin films including various quantities of Eu atoms (from 0 to 10 at.%) were synthesized on glass slides. The detailed physical properties of the produced CdS and CdS:Eu thin films were explored. Structural analysis showed that Eu-doping enhanced the crystal quality of CdS thin films until 10 at.% Eu-doping and further Eu-doping treatment led to a distortion in the CdS structure. In addition, the crystallite sizes of CdS thin films dropped from 36.2 to 32.4 nm as Eu-doping level increased to 10 at.%. Morphological data showed that increasing Eu-doping remarkably varied the surface morphology of CdS thin films forming smaller grains. Chemical content examinations approved the presence of Eu atoms in CdS structure. From the optical measurements, it was obtained that more transparent CdS thin films with a maximum transmittance of 68% at 820 nm were created after 10 at.% Eu-doping and bandgap values of samples reduced from 2.58 to 2.47 eV with rising of Eu-doping from 0 to 10 at.%. Room temperature photoluminescence data demonstrated the formation of two essential peaks for all the samples, which are in turn related to green and yellow bands. Electrical investigation pointed out that Eu-doping enhanced the carrier density of CdS thin films from 4.38 × 1013 cm− 3 to 2.46 × 1014 cm− 3 and dropped the resistivity of CdS samples from 2.59 × 104 Ω cm to 5.85 × 103 Ω cm until 6 at.% and further increment of Eu-doping paved the way to get worse electrical data. Thus, it can be brought a conclusion that Eu-doping not only improved the optical properties of CdS thin films, but also restored the electrical properties, which are able to use in the opto-electronic devices.

Structure and Cathodoluminescence of Y2O3:Eu Thin Films obtained at Different Conditions

Structure and Cathodoluminescence of Y₂O₃:Eu Thin Films obtained at Different Conditions

Structure and Cathodoluminescence of Y2O3:Eu Thin Films obtained at Different Conditions

Structure and Cathodoluminescence of Y2O3:Eu Thin Films obtained at Different Conditions

Efficient optical activation of Eu3+ ions doped in ZnGa2O4 thin films: Correlation between crystalline phase and photoluminescence

The physicochemical properties of Eu-doped zinc gallate (ZnGaxO1+1.5x:Eu) (1 < x < 6) thin films were investigated by means of photoluminescence (PL) triggered by band-to-band transitions of the host crystal at λ = 325 nm. Close correspondence between PL spectra and crystalline phases was verified by performing combinatorial measurements over four-inch substrates on which there was a spread of Ga/Zn composition ratios. The phase formation kinetics for deposition with H2O as an oxygen source gas followed by post annealing were similar to those of hydrothermal synthesis. ZnGa2O4 preferentially formed for a wide range of compositions between 1 < x < 4 and post annealing temperatures between 400 and 800 °C; intense emissions from Eu3+ ions were observed from the films. In contrast, the phase formation kinetics for deposition with O2 gas followed by post annealing were similar to those of solid-state reactions. Vacuum annealing above 500 °C caused preferential losses of Ga atoms and precipitation of Zn2Ga2O5 crystallites at x < 4, whereas ZnGa2O4 formed when a large amount of Ga (x > 6) was initially contained in the as-deposited state. The resulting PL spectra from Zn2Ga2O5 exhibited only a broad emission band from 450 to 700 nm, which was ascribed to defects in the poorly crystallized Zn:Ga = 1:1 phase. When the films deposited with O2 were post annealed in an O2 ambient, Zn atoms were lost, producing β-Ga2O3 as the primary phase accompanied with ZnGa2O4. The resulting Eu3+ emission was very weak, possibly because the Eu3+ ions attached to Ga2O3 domains were not emission-active and/or could not be efficiently excited due to wide bandgap (5 eV). When ZnGa2O4:Eu films were crystallized during deposition at elevated temperatures, weak emissions only from Eu3+ ions were observed. Taken together, these experimental results indicate that Eu3+ ions attached to ZnGa2O4 are highly emission-active; i.e., ZnGa2O4 is a particularly good host crystal with which to secure optical activation of doped Eu3+ ions.

Structure and Cathodoluminescent Properties of Y2O3:Eu Thin Films at Different Activator Concentrations

The surface structure and cathodoluminescence (CL) spectra of thin films of Y2O3:Eu obtained by HF ion plasma sputtering were investigated by varying the activator concentration in the range of 1.0–7.5 mole%. The possibility of creating irregular solutions of yttrium and europium oxides and the structural features of the small and large crystallites that form the Y2O3:Eu film were demonstrated on the basis of the shape of the CL spectra at different activator concentrations. The critical distance for interaction between the Eu3+ ions at nodes with C2 and C3i point symmetry was estimated, and a mechanism of energy migration between these centers was proposed.

Electrical and Ferroelectric Properties of Rare-earth-doped Na$_{0.5}$Bi$_{4.0}RE_{0.5}$Ti$_4$O$_{15}$ ($RE$ = Eu, Gd and Dy) Thin Films

Electrical and Ferroelectric Properties of Rare-earth-doped Na$_{0.5}$Bi$_{4.0}RE_{0.5}$Ti$_4$O$_{15}$ ($RE$ = Eu, Gd and Dy) Thin Films

Cathodoluminescence of Y2O3:Eu Thin Films Obtained by RF Sputtering

The cathodoluminescent (CL) properties of Y2O3:Eu thin films obtained by RF magnetron sputtering were investigated. The number of Eu3+ ions in C2 states of lower symmetry was hypothesized to be greater in the film bulk than on the surface based on studies of the CL spectral intensity as a function of the exciting-electron energy and current density. It was shown that film structural defects and the excitation conditions influenced the kinetic characteristics of the red emission of Y2O3:Eu at 612 nm that was due to the electric dipole transition 5D0 –7F2.

Photoluminescence study of Eu+3 doped ZnO nanocolumns prepared by electrodeposition method

Europium doped ZnO (ZnO:Eu) nanocolumns were grown on indium tin oxide substrates (ITO) by electrodeposition method in zinc nitrate aqueous solution with different concentration of Eu. According to XRD results electrodeposited ZnO:Eu films exhibit thigh crystalline quality with a preferential orientation parallel to c-axis. Moreover, the (002) peak position shifts toward to lower angles confirming the incorporation of Eu+3 ions into the ZnO lattice. The crystallite size of a pure ZnO decreases when increasing the Eu doping. SEM images reveal a well dense nanocolumns arrays perpendicular to the surface. Furthermore, doping with Eu+3 ions leads to a change in the top of nanocolumns from hexagonal to conic-hexagonal shape. The average diameters of nanocolumns are found to be around 200nm and 180nm for undoped ZnO and Eu doped ZnO, respectively. Photoluminescence (PL) emission from ZnO:Eu thin films reveals the typical peaks related to excitons and intrinsic defects in ZnO and four narrow peaks in the red region attributed to 4f-shell transition in Eu+3 ions. As Eu doping increased, PL peaks related to Eu+3 emission showed an increase in intensity and a shift in its wavelength position. A schematic drawing of the excitation mechanism and related emission process is proposed.

Influence of Obtainment Conditions and Excitation Into Spectral and Kinetic Characteristics of Cathodoluminescence in Y2O3:Eu Thin Films

The spectra and kinetics of the rise and decay of the cathodoluminescence (CL) of thin films of Y2O3:Eu obtained by RF-magnetron sputtering were investigated. Based on the shape of the CL spectra at different excitation energies, it showed the possibility of creating irregular solutions of yttrium and europium oxides and the structural features of the surface and bulk layers. The time constant for the decay CL for 612 nm emission was determined and the value of which is within the range (1.8 - 4.1) ms. This value is a complex function of the type of film deposition atmosphere, the activator concentration, and the duration of the exciting pulses was shown. The features of the risen CL and the proposal based on the delayed rise CL analyze structural perfection of Y2O3:Eu thin films.

Physicochemical analysis of Bi2Te3 – (Fe, Eu) – Bi2Te3 junctions grown by molecular beam epitaxy method

Topological insulators (TI) are a class of materials gaining in importance due to their unique spin/electronic properties, which may allow for the generation of quasiparticles and electronic states which are not accessible in classical condensed-matter systems. Not surprisingly, TI are considered as promising materials for multiple applications in next generation electronic or spintronic devices, as well as for applications in energy conversion, such as thermo-electrics. In this study, we examined the practical challenges associated with the formation of a well-defined junction between a model 3D topological insulator, Bi2Te3, and a metal, Fe or Eu, from which spin injection could potentially be realized. The properties of multilayer systems grown by molecular beam epitaxy (MBE), with Fe or Eu thin films sandwiched between two Bi2Te3 layers, were studied in-situ using electron diffraction and photoelectron spectroscopy. Their magnetic properties were measured using a SQUID magnetometer, while the in-depth chemical structure was assessed using secondary ion mass spectroscopy. An examination of impact of Bi2Te3 structure on chemical stability of the junction area has been realized. For Fe, we found that despite room temperature growth, a reaction between the Fe film and Bi2Te3 takes place, leading to the formation of FeTe and also the precipitation of metallic Bi. For the Eu tri-layer, a reaction also occurs, but the Te chemical state remains intact.

Pure and strong red photoluminescence from Na0.5Gd0.5TiO3: Eu ferroelectric thin films under ultraviolet light excitation

A series of novel photoluminescent ferroelectric thin films Na0.5Gd0.5TiO3: xEu (NGT: Eu) with various Eu3+ doping concentrations were prepared at various heat-treated temperature, which have single pseudo-cubic perovskite structure at proper heat-treated temperature from 700 °C to 800 °C according to X-ray diffraction results. There existed narrow and intensive emission bands located at red light region ascribed to 5D0 → 7F2 and 5D0 → 7F1 transitions of Eu3+ by 283 nm excitation. The strong energy absorption of NGT host and efficient energy transfer to Eu3+ should be primarily responsible for the emissions. Gd3+ acts as sensitizer which has an important role on the energy transfer from the host NGT to Eu3+. The luminescence from NGT: 0.25Eu thin films is the strongest for all the NGT: Eu films, and its color coordinate is (0.65, 0.32) close to ideal red light. The quenching concentration in NGT: Eu films reaches as high as 25%. The lifetime of emissive energy level Eu3+: 5D0 in NGT: 0.1Eu and NGT: 0.5Eu thin films is 1.024 ms and 0.931 ms, respectively. Finally, the ferroelectric property of NGT: 0.25Eu thin films was tested and the remanent polarization (2Pr) is 7.10 μC/cm2 lower than that of Na0.5Bi0.5TiO3.

Effect of europium content on physical properties of In2O3 thin films for sensitivity and optoelectronic applications

In2O3 : Eu thin films were successfully grown by spray pyrolysis. XRD studies showed that the films had In2O3 cubic structure with (004) preferential orientation and best crystal properties at 1.5% Eu doping level. The optical band gap energy decreased with Eu content around 4.1 eV. Urbach energy was of the order of 278 meV, it decreased with Eu content which indicates a decrease in the defects by doping. The dispersion of the refractive index was discussed. Raman spectroscopy showed the band positions corresponding to In2O3 cubic phase with a small shift related to europium incorporation within In2O3 matrix. PL measurements showed a large band which was located at 410 nm and related to the band-to-band transitions and other bands related to impurity levels. Finally, the electric conductivity was investigated depending on the effect of temperature. Activation energy was found to range from 45 to 60 meV for films which were prepared with 1% Eu content.

Guided-mode resonance assisted directional emission of a wavelength-shifting film for application in scintillation detection.

Thin-film luminescent layers as wavelength shifters using in the scintillation detection system suffer with low efficiency due to the total internal reflection and the non-directional emission. In the present work, we design and fabricate a photonic crystal on the surface of LuTaO(4):Eu(3+) thin-film which is a newly developed luminescent material using in radiation detection systems. The entire structure shows guided-mode resonances with only one TE and TM mode. As a result, the emitting light is effectively extracted. Furthermore, due to only two modes existing in the layer, the directionality of emission is strongly controlled. This result enables the structured LuTaO(4):Eu(3+) thin-film to be a potential wavelength shifter with high-efficiency.

Nanoscale determinant to brighten up GaN:Eu red light-emitting diode: Local potential of Eu-defect complexes

Emission sites in GaN:Eu red light-emitting diodes (LEDs) were investigated using a new spectroscopy technique, namely, site-selective pulse-driven emission spectroscopy (PDES). The PDES, in which the emission intensity of a pulse-driven LED is recorded with respect to the pulse frequency, revealed the charge-trapping dynamics of the Eu emission sites. We found that a determinant of the emission intensity of the sites was not their relative abundance, but rather the spatial extent of the local potential, which determines the effectiveness of the capture of injection charges. Minor sites with wider potentials enhanced the emission intensity of the LED, resulting in emission spectra that differ from those obtained using the photoluminescence of a GaN:Eu thin film. The potential curve is determined by the atomic structure of the complexes, which consist of a Eu dopant and nearby defects in the GaN host. The extent was characterized by a parameter, namely, cutoff frequency, and the emission sites with the wider and narrower potentials in the GaN:Eu LED were found to have cutoff frequencies of 400 kHz and 3 MHz, respectively. The cutoff frequency of 3 MHz was found to be the upper limit for emission sites in the LED. The emission site with the wider potential is useful for slower devices such as light fixtures, while the site with the narrower potential is useful for faster devices such as opto-isolators.

Effect of Post-Annealing on the Properties of Eu Doped ZnO Nano Thin Films

Europium (Eu) doped nanostructure ZnO thin films are prepared by using spray pyrolysis technique. The ZnO:Eu thin films are deposited at a substrate temperature of 623K on glass substrates, using europium nitrate as a Eu source. The as-prepared ZnO:Eu films are annealed in air at 673K and 723K for 1h. The effect of post-annealing on the structural, electrical and optical properties of the films has been studied. XRD measurements show that all the films are nanocrystallized in the hexagonal wurtzite structure and exhibit a preferential orientation along (002) plane, the intensity of preferentially oriented (002) peak is apparently improved. The resistivity of annealed film is larger than the as-deposited. ZnO:Eu film annealing at 723K for 60min exhibits lowest resistivity of 3.62×10-4Ω cm. In addition, the ZnO:Eu film shows good optical transmittance of 94%.

Long lasting blue phosphorescence and photostimulated luminescence in 12CaO⋅7Al2O3:Eu thin films grown by pulsed laser deposition

Long lasting blue emitting Eu-doped 12CaO⋅7Al2O3 thin films have been prepared on quartz substrates by pulsed laser deposition combined with post-annealing. The 12CaO⋅7Al2O3 phase is formed after annealing the films above 900°C in vacuum ambient. Upon 323nm excitation, the thin films exhibit a blue long lasting emission peaked at 444nm, assigned to the 5d–4f transitions of Eu2+. The films annealed at 950°C have stronger luminescence and longer lasting time than that annealed at 900°C. The phosphorescence intensity of vacuum annealed film is better than that annealed in H2/N2 atmosphere, which might be due to the increase of shallow trap numbers during the vacuum annealing process. Thermoluminescence curves demonstrate that vacuum and H2/N2 atmosphere annealing could introduce a large number of both shallow and deep traps into 12CaO⋅7Al2O3:Eu thin films. After UV irradiation, excellent photostimulated luminescence can be observed under 980nm excitation. Our results suggest that 12CaO⋅7Al2O3:Eu phosphor may serve as a promising blue luminescent materials used in fabrication of optical storage and illumination in dark environments.

Tunable photoluminescent properties of Eu-doped β-Ga2O3 phosphor thin films prepared via excimer laser-assisted metal organic decomposition

A Ga2O3:Eu thin film was prepared via excimer laser-assisted metal organic decomposition (ELAMOD) using an ArF laser at RT, and the effects of temperature and laser fluence during irradiation on the photoluminescent (PL) properties were investigated. Direct irradiation of the precursor film comprising metal organic compounds was found to be effective for obtaining excellent PL properties. Moreover, as the laser fluence of the ArF laser used changed, the PL intensity ratio of the peaks at 511 and 614 nm accordingly changed. The color coordinates of the β-Ga2O3:Eu3+ thin films prepared by ELAMOD were x = 0.43 and y = 0.38. On the other hand, β-Ga2O3 films prepared via ELAMOD at fluences of 100 and 150 mJ/cm2 exhibited a strong broad blue-green emission band with a peak wavelength of approximately 421 nm. The emission mechanism of the Ga2O3:Eu films prepared via ELAMOD was also investigated.

Structural and electrical studies on rare-earth-element-substituted (Bi0.9 A 0.1)(Fe0.975Ti0.025)O3+δ (A = Nd, Gd, Eu) thin films

Pure BiFeO3 (BFO) and rare-earth-metal-ion co-substituted (Bi0.9A0.1)(Fe0.975Ti0.025)O3+δ (A = Nd, Gd and Eu, denoted by BNdFTi, BGdFTi, and BEuFTi, respectively) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates via a chemical solution deposition method. A perovskite-based-distorted rhombohedral structure for the thin films were confirmed by using an X-ray diffraction and a Raman scattering analysis. Significant improvements in the electrical and the ferroelectric properties were observed for the co-substituted thin films. For the BGdFTi and the BEuFTi thin films, the measured leakage current densities were 8.17 × 10−5 A/cm2 and 4.96 × 10−5 A/cm2 at an applied electric field of 100 kV/cm, respectively, which are approximately three orders of magnitude lower than that of the pure BFO thin film. Furthermore, a large remnant polarization (2Pr) of 99.0 µC/cm2 at 1470 kV/cm was measured for the BGdFTi thin film.

Wet chemical preparation of YVO4:Eu thin films as red-emitting phosphor layers for fully transparent flat dielectric discharge lamp

Highly transparent YVO4:Eu thin films were deposited via dip coating of liquid nanoparticle dispersions on glass substrates. Annealing of the nanoparticle layers resulted in restructuring of the material into oriented crystalline films. The crystallinity was confirmed using powder X-ray diffraction. Film thickness was adjusted to 467nm by multiple deposition. The resulting coatings show >99% absorbance for wavelength below 300nm and >90% transmission in the visible spectral range. Under UV-light excitation a bright red photoluminescence with a quantum efficiency of 20% is observed. A planar, transparent dielectric barrier discharge lamp was constructed using YVO4:Eu coated glasses and transparent electrodes made from antimony-doped tin dioxide thin films.

Growth of europium-doped gallium oxide (Ga2O3:Eu) thin films deposited by homemade DC magnetron sputtering

Europium-doped gallium oxide (Ga2O3:Eu) thin films have successfully been grown using direct current magnetron sputtering by means of Eu concentration variation. Energy-dispersive X-ray spectroscopy spectra indicate gallium, oxygen, and europium elements as the growing films' chemical compositions. Based on scanning electron microscopy images, the morphology of Ga2O3:Eu thin film is seemingly like a granulated nano-size configuration. In this study, UV-visible spectrophotometer results show that the variation of Eu doping concentration inflicted no change toward the optical bandgap of the growing films. The optical bandgaps of undoped Ga2O3 film and Ga2O3:Eu film were seen to be relatively similar, i.e., approximately 3.4 eV. Yet, the presence of Eu doping in Ga2O3 configuration had led to blueshift phenomenon when the concentration was 2% and redshift phenomenon when it was 5%. Photoluminescence emissions of all samples were observed in the red area with the emission peak between 593 and 602 nm.