Eu Thin Films Research Articles

Cathodoluminescence of yttrium oxide and yttrium and zinc silicate films

We have studied the cathodoluminescent properties of Y2SiO5:Ce, Zn2SiO4:Ti, Zn2SiO4:Mn, Y2O3:Eu thin films obtained by high-frequency magnetron sputtering. Based on measurements of the luminescence spectra, we have shown that the films can be used as luminophores with blue emission (Y2SiO5:Ce, Zn2SiO4:Ti), green emission (Zn2SiO4:Mn), and red emission (Y2O3:Eu). We have studied the dependences of the luminescence intensity on the energy of the exciting electrons, the electron beam current density, and the exposure time. We hypothesize that the decrease in the luminescence intensity during electron bombardment is connected with formation of new oxide layers as a result of an electron-stimulated surface chemical reaction.

LaVO 4 : Eu Phosphor films with enhanced Eu solubility

Eu doped rare-earth orthovanadates are known to be good red phosphor materials. In particular, LaVO4:Eu is a promising candidate due to the low Eu-site point symmetry, and thus high dipole transition probability within Judd–Ofelt theory. However, the low solubility limit (<3 mol %) of Eu in LaVO4 prevents its efficient use as a phosphor. We present optical evidence of enhanced Eu solubility as high as 10 mol % in LaVO4:Eu thin films grown by pulsed laser deposition and postannealing. The photoluminescent intensity exceeded that of YVO4:Eu thin films when excited below the host bandgap, indicating stronger direct emission of Eu in LaVO4.

Multiferroic Properties of Rare-Earth Eu and Nd Doped BiFeO3 Thin Films

Pure BiFeO3 (BFO), Eu doped BFO (BEF), and Nd doped BFO (BNF) multiferroic films were prepared by pulsed laser deposition on Pt/Ti/SiO2/Si substrates. XRD analysis revealed that the films had the rhombohedral structure with doping-induced lattice distortion. The Eu and Nd doping significantly improved the dielectric, ferroelectric, and ferromagnetic properties of the BFO films. Saturated hysteresis loops were observed in BEF and BNF films with remnant polarization of 37 μC/cm2 and 60 μC/cm2, respectively. The magnetization was demonstrated with remnant magnetization of 0.10 emu/cm3 and 0.60 emu/cm3 for the BEF and BNF films, respectively. The improvements and mechanism of different element doping on the properties of the BFO films were discussed.

Preparation of Y2O3:Eu thin films by excimer-laser-assisted metal organic deposition

Europium-doped yttrium oxide (Y2O3:Eu) thin films were successfully deposited on quartz and ITO/glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) at low temperatures. The effects of laser wavelength and thermal temperature on the films’ crystallinity and photoluminescence properties were investigated. Films irradiated by an ArF laser at 80 mJ/cm2 and 400–500°C were highly crystallized compared with those prepared by thermal MOD. In contrast, when the film was irradiated by a KrF laser at 500°C, no crystalline Y2O3:Eu was formed. The Y2O3:Eu film irradiated by the ArF laser at 80 mJ/cm2 and 500°C showed typical PL spectra of Eu3+ ions with cubic symmetry and a 5D0→7F2 transition at ∼612 nm. The PL intensity at 612 nm was much higher for the film prepared with ELAMOD than for that prepared by the thermal-assisted process, and the photoemission intensity of the film prepared with ELAMOD strongly depended on the substrate material.

Photoluminescence of Eu3 + -Doped Ba0.7Sr0.3TiO3 Thin Film for Optoelectronic Application

The europium-doped barium strontium titanate (BST:Eu) films find application in ferroelectric as well as in optoelectronic devices. In this paper, we report the pulsed laser deposition (PLD) of BST:Eu thin films. The structural and optical properties of the PLD-grown BST film have been investigated and correlated. The photoluminescence spectra show the prominent transitions of ions at 550 nm , 615 nm , and 669 nm upon excitation with 408 nm. The luminescent properties of BST:Eu thin films follow a close correlation with the crystallinity of the thin films. Films deposited at a lower substrate temperature show good luminescent characteristics.

Electrical and magnetic properties of GaN codoped with Eu and Si

GaN thin films codoped with Eu and Si were grown on sapphire by solid source molecular beam epitaxy technique. Si incorporation changed GaN:Eu thin films from highly resistive to n-type conductive but not to levels normally achieved in conventional Si-doped GaN films. The magnetic properties of the codoped GaN films were measured by an alternating gradient magnetometer. While all samples exhibited hysteresis behavior at room temperature, there was a marked dependence on the Si codoping. At low-to-moderate Si doping levels, an increase up to approximately nine times in saturation magnetization was observed for films having higher conductivity, which also displayed an anomalous Hall effect. Under illumination at 371 nm, an increase in saturation magnetization was observed for all samples.

Effect of growth conditions on Eu 3+ luminescence in GaN

Eu-doped GaN thin films were in situ grown on sapphire substrates by RF plasma-assisted solid-source molecular beam epitaxy technique. Strong red emission at ∼622 nm from 5D 0– 7F 2 radiative transitions in Eu 3+ ions was observed for all samples. The effects of important growth parameters, such as III/V ratio (Ga flux), Eu cell temperature (Eu flux) and growth temperature, on Eu 3+ photoluminescence were studied. X-ray diffraction and secondary ion mass spectroscopy measurements were performed to investigate thin film quality and Eu doping profiles. The strongest Eu 3+ luminescence was obtained from GaN:Eu thin films grown under slightly N-rich condition (III/V<1), while the highest Eu 3+ emission efficiency was obtained in thin films grown under Ga-rich condition (III/V≥1). The optimum Eu doping concentration for Eu 3+ luminescence is ∼(0.1–1.0) at% for III/V≤1 ratio condition. Higher growth temperature (>750 °C) was also found to enhance Eu 3+ luminescence intensity and efficiency.

Preparation of High-luminance SrGa2S2:Eu Thin Film Phosphors by Laser Annealing

Preparation of green-emitting SrGa2S4:Eu thin film phosphors by low temperature process at lower than 600oC under an assist with a laser annealing technique after the deposition was investigated. It was shown that the crystallinity and emission intensity of the SrGa2S4:Eu film annealed at 500oC were improved considerably by the assist with laser annealing using KrF excimer laser. As a result, the film showed cathodoluminescent (CL) luminance of about 2,000 cd/m2 under excitation with 5kV and 60uA/cm2. It was found from these results indicate that the laser annealing technique assists the improvement of both structural and luminescent properties.

Preparation of High-Luminance SrGa2S4:Eu Thin Film Phosphors by Laser Annealing

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Linear and nonlinear optical properties of rare earth doped of Ba0.7Sr0.3TiO3 thin films

Ba0.7Sr0.3TiO3:Eu ferroelectric films were deposited on quartz substrates by pulsed laser deposition. The linear absorption coefficient and the linear refractive index calculated from the transmission spectrum at 532 nm were found to be 1.67×104 cm−1 and 1.82 respectively. The room temperature photoluminescence shows the characteristic emission of Eu3+ ions. The nonlinear optical properties of the film were investigated by a single beam Z-scan setup. The negative nonlinear refractive index and two photon absorption coefficient was found to be −1.508×10−6 m2/GW and 240 m/GW respectively. The real and imaginary part of the third order susceptibility of the thin films is 2.58×10−17 m2/V2 and 1.16×10−16 m2/V2 respectively. The BST:Eu thin films show good optical limiting property.

Templated growth of textured and luminescent CaS : Eu thin films by a low-temperature solvothermal process

The direct growth of luminescent sulfide thin films onto templated substrates was realized with a solvothermal synthesis method. The as-grown layers of SrS : Eu and CaS : Eu emit a bright and homogeneous photoluminescence, peaking at 610 nm and 650 nm, respectively. X-ray diffraction measurements showed that the layers grown at a temperature of only 200 °C are strongly crystalline, with (2 0 0) out-of-plane orientation. Using silicon substrates, almost epitaxial growth could be obtained. Electron microscopy was used to study the growth, morphology and texture of the thin films. The main advantages of this innovative approach for the production of sulfide layers are the low-temperature process and scalability.

Photoluminescence and electroluminescence from Eu-activated CaAl2O4-based multicomponent oxide thin-film phosphors

Photoluminescence (PL) and electroluminescence (EL) from newly developed Eu-activated CaAl2O4 -based multicomponent oxide phosphor thin films prepared by rf magnetron sputtering are described. Yellowish green and blue emissions in PL were obtained in as-deposited and postannealed ((CaAl2O4)1−x–(BaAl2O4)x):Eu and ((CaAl2O4)1−x–(MgAl2O4)x):Eu thin films, respectively. In addition, blue emission in EL was observed from thin-film electroluminescent (TFEL) devices fabricated by using ((CaAl2O4)1−x–(BaAl2O4)x):Eu thin films postannealed at 1000°C in an Ar+H2(5%) gas atmosphere. A luminance of 3.2cd∕m2 for blue emission was obtained in a ((CaAl2O4)0.44–(BaAl2O4)0.56):Eu TFEL device driven by a 1kHz sinusoidal wave ac voltage; the blue EL emission corresponds to the CIE color coordinates of (x=0.24, y=0.13).

Spatially resolved cathodoluminescence of luminescent materials using an EDX detector

Panchromatic cathodoluminescence (CL) maps were collected in a scanning electron microscope equipped with an EDX (energy dispersive x-ray analysis) detector. These CL maps can readily be correlated with elemental maps obtained by EDX. Although EDX detectors are designed to be insensitive to light and therefore not optimized for high sensitivity CL measurements, high-resolution images can be obtained from luminescent materials without the need for additional hard- or software. The method was tested on highly luminescent BaAl(2)S(4):Eu(2+) thin films that have a potential use in flat panel displays. The spectral response and linearity of the overall system was determined by means of monochromatic light sources, illuminating the sample through an optical fibre. We studied the response of the EDX detector to the intensity of the incoming light as well as the influence of the detector settings. The observations were explained by numerical simulations.

Magnetic properties of insulating RTiO3 thin films

The magnetic properties of epitaxial RTiO3 (R = Y, Eu) thin films are reported. The films were grown on various substrates with different lattice mismatches using the pulsed laser deposition technique. Ferromagnetic YTiO3 thin films could only be grown on LaAlO3 (110) substrates, while EuTiO3 films could be grown on various substrates. The magnetic properties of the grown films are discussed in light of the structural characterization.

Influence of annealing on the structure and stoichiometry of europium-doped titanium dioxide thin films

This work presents the influence of annealing on the structure and stoichiometry of europium (Eu)-doped titanium dioxide (TiO 2). Thin films were fabricated by magnetron sputtering from a metallic Ti–Eu target in oxygen atmosphere and deposited on silicon and SiO 2 substrates. After deposition the selected samples were additionally annealed in air up to 1070 K. Film properties were examined by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) and the results were analyzed together with the undoped TiO 2 thin films prepared under similar technological conditions. XRD results showed that depending on the Eu content, as-deposited thin films consisted of the TiO 2-anatase or TiO 2-rutile. An additional annealing will result in the growth of anatase crystals up to 35 nm, but anatase to rutile phase transformation has not been recorded. AFM images display high quality and a dense nanocrystalline structure. From the XPS Ti2p spectra the 4+oxidation state of Ti was confirmed. The O1s XPS spectra displayed the presence of an O 2− photoelectron peak accompanied by an additional broader peak that originates from hydroxyl species chemisorbed at the sample surface. It has been found that Eu dopant increases the OH − content on the surface of prepared TiO 2:Eu thin films. The calculated O/Ti ratio was in the range of 1.85–2.04 depending on the sample.

Cathodoluminescent Properties of Sol-Gel Derived Gd&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;:Eu Thin-Film Phosphors on Sapphire Substrates

Gd 2 O 3 :Eu thin-film phosphors were fabricated on sapphire substrates using a simple Pechini-type sol-gel process. The films were annealed at various temperatures between 700 and 1200°C for 2 hours in air after deposition. The sol-gel process enabled the synthesis of efficient Gd 2 O 3 :Eu thin-film phosphors with good optical properties, high crystallinities and smooth morphologies and a thickness of 1.5 μm. The Gd 2 Ο 3 :Eu thin film annealed at 1200°C had a thickness of 1.5 μm and exhibited a CL luminance of-124 cd/m 2 and CIE coordinates of (0.64, 0.35) under 5 kV e-beam excitation at 10 μA. A significant improvement (by a factor of-10) was found in the aging characteristics of the Gd 2 O 3 :Eu thin-film phosphors under 5 kV CL excitation (an electron dose of 10 μA/cm 2 DC for 1100 min) compared to those of commercialized Y 2 O 3 :Eu powder phosphors.

Hydrogen Plasma Process to Reduce the Eu-Doped Sr&lt;sub&gt;2&lt;/sub&gt;SiO&lt;sub&gt;4&lt;/sub&gt; Thin Films

As-grown Sr2SiO4:Eu thin films on Si (100) substrates have been reduced by hydrogen plasma reaction which was carried out by using radio frequency plasma enhanced chemical vapor deposition system. The photoluminescence spectra, the crystal structure and the surface morphologies of the plasma-reduced films were measured and compared with those of the as-grown films. At as-grown state, Eu3+ and Eu2+ ions co-exist so that the photoluminescence spectra of the films reveal several emission bands between 350 and 650 nm. They were due to f-f and f-d transitions within Eu3+ and Eu2+ ions. After the plasma-reduced process, the photoluminescence spectra of the films show a remarkable increase of blue-green emission from the transitions of Eu2+ ions and decrease of red emission from the transitions of Eu2+ ions.

P‐87: Flux Effects on BaAl2S4:Eu, F Blue‐phosphor

AbstractBlue‐emitting BaAl2S4:Eu phosphor thin‐films was achieved under low temperature annealing. Phosphor thin‐films are deposited with using EuF3 as a Eu‐source. Crystal structure of BaAl2S4:Eu thin films deposited with fluorine have orthorhombic structure. The relationship between the optical properties and crystal structure is also studied.

Optical Properties of Blue-Emitting BaAl 2S 4:Eu Thin-Films for Inorganic EL Display

The optical properties of blue emitting BaAl 2S 4:Eu thin-films were studied. The emission peak is around 470 nm, whose FWHM (full width at half maximum) is 35 nm. The dielectric constant is 3.03 from transmission spectrum, and the optical band gap is approximately 4.6 eV. It is found that the cubic phase and orthorhombic phase exist in fabricated thin-films. Furthermore, the energy band structure of BaAl 2S 4:Eu thin-films from X-ray photo-electron spectra (XPS) and the absorption spectra were analyzed.

Analysis of the factors governing the enhanced photoluminescence brightness of Li-doped Y2O3:Eu thin-film phosphors

The authors studied the Li concentration dependence of the internal efficiency and extraction efficiency contributions to the enhanced photoluminescence (PL) brightness of the Li-doped Y2O3:Eu thin films. Experiments conducted with excitation at a wavelength of 254nm showed that adding 20mol% Li2CO3 to conventional Y2O3:Eu thin films improved their PL brightness by a factor of over 7.0. This improvement is attributed to enhanced internal factors (crystallinity, grains, and substitution of interstitial oxygen) and the increased optical volume (thickness), as well as the reduction of photon trapping in the high-index guiding layers of the Y2O3:Eu thin films. They also discuss how to quantitatively determine the contributions of the internal efficiency, the extraction efficiency, and the optical volume to the enhanced PL brightness of the Li-doped Y2O3:Eu thin-film phosphors.