Phosphor Thin Films Research Articles

Synthesis and luminescence characterization of manganese-activated willemite gel films

Manganese-activated willemite (α-Zn 2 − x Mn xSiO 4; x = 0.05–0.20) phosphor thin films with bright green light emission were deposited on silicon wafers by a sol–gel process. Zinc chloride, tetraethylorthosilicate, and manganese chloride were employed as precursors. The sol–gel transition, crystallization process and photoluminescence of processed films were investigated. The level of manganese doping did not greatly affect the crystallinity, but did affect the gelation rate and luminescence of films. X-ray diffraction and infrared spectrum studies revealed that single-phase willemite started to crystallize at around 600 °C. After thermal annealing at 600°–1200 °C, the crystallinity of films increased with increasing heating temperature and thickness of films. The emission intensity of the film was strongly related to the crystallinity and deposition conditions. Controlling the dopant content, number of coating layers and annealing temperature could significantly enhance the brightness of the green emission. The luminescence properties of α-Zn 2SiO 4:Mn films are characterized by fluorescence spectra and decay lifetime measurements.

Greatly improved photoluminescence properties of the electrodeposited Y 2O 3:Eu 3+ thin film phosphors by the addition of Na + and K + ions

In this work, Y 2O 3:Eu 3+ thin film phosphors were prepared by electro-deposition method. The effect of Na + and K + ions on the photoluminescence properties of Y 2O 3:Eu 3+ thin film phosphor was studied in details. It was found that the addition of Na + and K + ions could improve the photoluminescence intensity by 3 to 4 times. The highly improved photoluminescence intensity may be caused by different factors. The improved crystallinity and the increased optical volume caused by the flux effect of Na + and K + ions could be the major reasons for the enhanced photoluminescence intensity. It was also found that the average lifetime of Y 2O 3:Eu 3+ thin film phosphors could be adjusted by the molar amount of Na + and K + ions.

P‐101: Synthesis of Transparent and Green‐emitting CaSO4: Tb3+, Na+ Thin Film Phosphors by RF Magnetron Sputtering

AbstractTransparent and green‐emitting CaSO4:Tb3+, Na+ thin film phosphors (TFPs) have been synthesized by RF magnetron sputtering, and their luminescence and optical properties were investigated. Transparent and green‐emitting CaSO4:Tb3+, Na+ TFPs were successfully synthesized at room temperature.

Color control of emissions from rare earth-co-doped La 2O 3:Bi phosphor thin films prepared by magnetron sputtering

Multicolor photoluminescence (PL) and electroluminescence (EL) were observed from developed Bi- and rare earth (RE)-co-doped La 2O 3 (La 2O 3:Bi,RE) phosphor thin films. The phosphor thin films were prepared with various contents of co-doped RE, such as Dy, Er, Eu, Tb and Tm, by a combinatorial radio frequency magnetron sputtering deposition method. The obtainable luminance in EL and PL intensities changed considerably as the kind and content of RE were varied. Color changes from blue and blue-green to various colors in PL and EL emissions, respectively, were obtained in postannealed La 2O 3:Bi,RE phosphor thin films: films prepared by co-doping Bi at a constant content with various REs at varying levels of content. However, all of the observed emission peaks in PL and EL from La 2O 3:Bi,RE phosphor thin films were assigned to either the broad emission originating from the transition in Bi 3+ or the visible emission peaks originating from the transition in the co-doped trivalent RE ion. The difference between PL and EL characteristics in La 2O 3:Bi,RE phosphor thin films is mainly attributed to the difference in the excitation mechanism.

Fabrication of Micro-Patterned 2D Nanorod and Nanohole Arrays by a Combination of Photolithography and Nanosphere Lithography

This paper reports a facile fabrication technique for micro-patterned two-dimensional (2D) nanorod and nanohole arrays. This technique is based on a combination of two simple and scalable processes: photolithography for micro-patterns and nanosphere lithography (NSL) for nano-patterns. Mixed patterns, such as micro-scale line patterned 2D SiO2 nanoarrays, can be routinely fabricated over a quartz substrate owing to the high reproducibility of this simple method. In micro-patterned 2D nanoarrays, the structural dimensions of micro-patterns can be controlled by general optimization of photolithography techniques; structural dimensions of nano-patterns can be controlled with the NSL technique. We demonstrate micro-patterned fluorescence images of SrGa2S4:Eu2+ thin-film phosphors (TFPs) by depositing TFPs on micro-patterned 2D SiO2 photonic crystal (PC) nanoarrays using rf-magnetron sputtering technique. It is expected that photolithography-assisted NSL will be incorporated easily in the fabrication of micro-patterned PC for the various photonic or optoelectronic devices.

Enhanced luminescence properties of Li-doped CaTiO 3:Pr 3+ thin films grown by PLD under various lithium ion contents

This paper reports the structural and luminescent properties of CaTiO 3:Pr 3+ and Li-doped CaTiO 3:Pr 3+ (0.0–5.0 wt.% Li) thin film phosphors deposited on an Al 2O 3 (0001) substrate using a pulsed laser deposition technique. The structural properties of these films were examined by X-ray diffraction, atomic force microscopy and Fourier transform infrared spectroscopy. The Li + concentration affected the crystallinity and surface morphology of the CaTiO 3:Pr 3+ thin films. The crystallinity and emission intensity increased with increasing Li + content from 0.0 wt.% to 1.0 wt.%. The dominant emission was from the 1D 2→ 3H 4 transition at 613 nm. 1D 2 emission quenching was also observed in the highly doped sample, which was related to the cross-relaxation process between Pr 3+ ions.

Luminescent Antireflective Coatings with Disordered Surface Nanostructures Fabricated by Liquid Processes

Antireflective phosphor coatings having disordered surface nanostructures were fabricated by a sol-gel dip coating method and a subsequent hot water treatment. Thin films of a Bi(3+),Eu(3+)-codoped YVO4 red phosphor were first prepared and effects of the addition of an aluminum source to precursor solutions on their microstructure and optical properties were examined. Optical transmittance of the YVO4:Bi(3+),Eu(3+) film was lower than that of a bare quartz glass substrate due to a higher refractive index of YVO4. The addition of the aluminum source and the hot water treatment resulted in a considerable increase of transmittance and its smaller angular dependence, which could generate an antireflective effect by the phosphor thin films. Observation of the microstructure revealed that the hot water treatment brought a remarkable change in the surface as well as the cross-section structure in the aluminum-added YVO4:Bi(3+),Eu(3+) film. The film density and hence the refractive index were gradually changed like a pseudo moth-eye structure, which explained the occurrence of the antireflective effect. The microstructural change was attributed to the dissolution of alumina present in the film and the reprecipitation of boehmite on the film surface during the hot water treatment. Photoluminescence of the YVO4:Bi(3+),Eu(3+) film could also be enhanced by the antireflective effect due to the suppression of surface Fresnel reflection of incident light and total internal reflection of emitted light.

ガラス基板上へのパターン化に成功した酸化亜鉛(ZnO)薄膜蛍光体 : スパッタリングによる薄膜成長、ウェットエッチング、熱処理を経て(発光型/非発光型ディスプレイ合同研究会)

ガラス基板上へのパターン化に成功した酸化亜鉛(ZnO)薄膜蛍光体 : スパッタリングによる薄膜成長、ウェットエッチング、熱処理を経て(発光型/非発光型ディスプレイ合同研究会)

Thin-film structure and fluorescence properties of sol-gel-synthesized Y2-xEuxO3 phosphors

Eu-doped yttria (Y2−xEuxO3) thin-film phosphors were prepared using a sol–gel process with post-annealing at 900°C. The Y2−xEuxO3 samples showed cubic bixbyite structure with a gradual increase in the lattice constant (≤0.5%) as x increases (≤0.22). The Eu-doped films exhibited strong photoluminescence (PL) near 2 eV at room temperature with well-resolved fluorescence peaks being ascribed to spin-flip f-f transitions, 5D0 → 7FJ (J = 0, 1, 2, 3, 4, 6), within trivalent Eu3+(f6) ion. Among the six fluorescence lines, the intensity of the strongest 2.03-eV line (J = 2) varies significantly with the Eu content and its optimum value for the maximum PL strength is likely to be near x = 0.1. The Eu-doped films on the Al2O3 substrates exhibited significantly higher PL intensities than those on the Si substrates despite no significant difference in structural properties between the two species being observed. It can be understood by comparing the change of complex refractive index for the Y2−xEuxO3/Al2O3 and Y2−xEuxO3/Si optical systems.

Novel Field Emission Organic Light Emitting Diodes with Dynode

This work presents novel field emission organic light emitting diodes (FEOLEDs) with dynode, in which an organic EL light-emitting layer is used instead of an inorganic phosphor thin film in the field emission display (FED). The proposed FEOLEDs introduce field emission electrons into organic light emitting diodes (OLEDs), which exhibit a higher luminous efficiency than conventional OLED. The field emission electrons emitted from the carbon nanotubes (CNTs) cathode and to be amplified by impact the dynode in vacuum. These field emission electrons are injected into the multi-layer organic materials of OLED to increase the electron density. Additionally, the proposed FEOLED increase the luminance of OLED from 10 820 cd/m^2 to 24 782 cd/m^2 by raising the current density of OLED from an external electron source. The role of FEOLED is to add the quantity of electrons-holes pairs in OLED, which increase the exciton and further increase the luminous efficiency of OLED. Under the same operating current density, the FEOLED exhibits a higher luminous efficiency than that of OLED.

Novel Field Emission Organic Light Emitting Diodes

This work presents a novel field emission organic light emitting diode (FEOLED), in which an inorganic phosphor thin film is replaced by an organic EL light-emitting layer in the configuration of a field emission display (FED). The field emission electrons emitted from the carbon nanotubes (CNTs) cathode of the proposed FEOLED intensify the electron density in the multi-layer organic materials of the OLED; thus, resulting a higher luminous efficiency than that of a conventional OLED. Additionally, the luminance of the proposed FEOLED can be further increased from 10,820 cd/m 2 to 27,393 cd/m 2 by raising the current density of OLED through an external electron source. A balanced quantity of electrons and holes in the OLED, which is achieved by the proposed FEOLED increases the number of excitons and attributes the enhancement of luminous efficiency of the OLED. Under the same operating current density, the proposed FEOLED exhibits a higher luminous efficiency than that of a conventional OLED.

Luminescent Properties of SrZnO2:Tb3+ Hybrid Thin Film Phosphors Grown by Pulsed Laser Deposition

Novel green-light-emitting Tb(3+)-doped SrZnO2 phosphor thin films were grown via the pulsed-laser-deposition technique. The films were grown at various substrate temperatures and oxygen pressures. The crystallinity and surface morphology of the films were investigated via X-ray diffraction (XRD) and atomic-force microscopy (AFM), respectively. The luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. The thin films showed a green emission radiated by the transitions from the 5D4 excited states to the 7FJ (J = 3-6) ground states of the Tb3+ ions found under ultraviolet excitation with a 272 nm wavelength. The crystallinity, surface morphology, and photoluminescence spectra of thin-film phosphors were found to be highly dependent on the deposition conditions, particularly the substrate temperature and oxygen pressure. The surface roughness and photoluminescence intensity of the films showed similar behaviors as a function of the substrate temperature and oxygen pressure.

High quality thin film phosphors of Y 2O 3:Eu 3+ deposited via chemical bath deposition

High transparency in visible region was required for red-light-emitting Y 2O 3:Eu 3+ thin film phosphors. Such films were obtained via chemical bath deposition on bare SiO 2 glass substrates through heterogeneous nucleation with further heat treatment. Thin amorphous yttrium basic carbonate films could be completely transformed to crystalline Y 2O 3 at 650 °C. X-ray diffraction and field-emission scanning electron microscopy were used to characterize these products. The deposition temperature and the post-annealing conditions were crucial factors for preparing high-quality thin films. The thin films prepared with optimized parameters emitted a bright red light around 612 nm. Meanwhile, these thin films exhibited optical transmittance of 90% to 95% in a wavelength range of 400 to 800 nm depending on the chemical deposition solution. These results clearly indicated that chemical solution deposition is a promising technique for large-scale production of thin film phosphors in application of display technology.

InGaN/GaN White Light-Emitting Diodes Embedded With Europium Silicate Thin Film Phosphor

This article describes the successful fabrication of europium-silicate thin film phosphor and its application to InGaN/GaN white light-emitting diodes (LEDs) in order to improve the photometric properties of the LEDs, including their correlated color temperatures (CCT) and color rendering index (CRI). The europium-silicate compounds are deposited on GaN templates grown on sapphire substrates by RF-sputtering and then annealed at 1000°C in an N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ambient to form a thin film phosphor that produces yellow or red emissions. The thin film phosphor is then patterned with stripes to grow a GaN buffer layer by epitaxially laterally overgrown GaN (ELOG) techniques, on which LED structures are grown by metal organic chemical vapor deposition. The ELOG sample shows no pits on the surface, and the full widths at half maximum (FWHMs) of its X-ray rocking curve for the (002) and (102) planes are as low as 249 and 416 arcsec, respectively. The optical spectrum from the embedded thin film phosphor is adjusted to have a maximum intensity at 560-600 nm and a FWHM as wide as 90 nm to make up for the low efficiency at these wavelengths of conventional YAG-based yellow phosphor. Finally, we observed a tristimulus coordinate (x, y) = (0.33, 0.39), CCT = 5607 K, and CRI = 77.6 from the white LEDs with thin film phosphor as compared with (x, y) = (0.30, 0.28), CCT = 8467 K, and CRI = 66.52 for the white LEDs without thin film phosphor.

An analysis of Y2O3:Eu3+ thin films for thermographic phosphor applications

A comparative study of the luminescent properties of Y2O3:Eu3+ phosphor powders and thin films sputtered from targets prepared from combustion synthesized powders is reported. Thin films of (Y0.96Eu0.04)2O3 were deposited on silicon substrates. Films deposited at 600 °C had both monoclinic and cubic phases of Y2O3, which developed to an oriented cubic phase after annealing. Films and powders showed a linear dependence of the intensity of the 5D7→7F2 (611 nm) transition with temperature in the range 26–660 °C with an average rate of change of 1.8×10−4 °C−1. The rate of change appears to be dependent on the Eu3+ concentration. This work shows that these thin films can be used as thermographic phosphors for remote temperature measurements.

Optical Properties and X-ray Absorption Fine Structure Analysis of ZnS:Cu,Cl Thin-Film Phosphors

ZnS:Cu,Cl thin-film phosphors have been studied for possible application to resin-free white light-emitting diodes (LEDs). The ZnS:Cu,Cl polycrystalline films grown by a molecular-beam deposition technique at relatively high substrate temperatures exhibit strong blue-green photoluminescence (PL). The films with a relatively high (∼1%) Cu concentration exhibit an enhanced near-UV excitation band as well as strong PL, making them suitable for excitation by UV LEDs; however, the transmission in the visible spectral range decreases. The X-ray absorption fine structure analysis of the phosphor films suggests that Cu atoms substitute for Zn sites at low Cu concentrations, whereas excess Cu atoms exist in a different form, possibly as CuS-like precipitates, at high Cu concentrations. The addition of Al donors to the phosphor films enhances the PL intensity and transparency, resulting from a reduction in the amount of the precipitates.

The growth of Y2SiO5:Ce thin films with pulsed laser deposition

Y2SiO5:Ce phosphor thin films were grown onto Si(100) substrates with pulsed laser deposition (PLD) using a 248-nm KrF excimer laser. Process parameters were varied during the growth process and the effect on the surface morphology and cathodoluminescence (CL) was analysed. The process parameters that were changed included the following: gas pressure (vacuum (5×10−6 Torr), 1×1−2 Torr and 1 Torr O2), different gas species (O2, Ar and N2 at a pressure of 455 mTorr), laser fluence (1.6±0.1 J cm−2 and 3.0±0.3 J cm−2) and substrate temperature (400 and 600°C). The surface morphology was investigated with atomic force microscopy (AFM). The morphology of the thin films ablated in vacuum and 10 mTorr ambient O2 showed more or less the same trend. An increase in the pressure to 1 Torr O2, however, showed a definite increase in deposited particle sizes. Ablation in N2 gas resulted in small particles of 20 nm in diameter and ablation in O2 gas produced bigger particles of 20, 30 and 40 nm as well as an agglomeration of these particles into bigger size clusters of 80 to 100 nm. Ablation in Ar gas led to particle sizes of 30 nm and the particles were much more spherically defined and evenly distributed on the surface. The higher fluence deposition led to bigger particle and grain sizes as well as thicker layers with respect to the lower fluence. The particle sizes of the higher fluence vary mainly between 130 and 140 nm and the lower fluence sizes vary between 50 and 60 nm. The higher fluence particles consist of smaller particles ranging from 5 to 30 nm as measured with AFM. The surface structure of the thin film ablated at 400°C substrate temperature is less compact (lesser agglomeration of particles than at 600°C). The increase in substrate temperature definitely resulted in a rougher surface layer. CL was measured to investigate the effect of the surface morphology on the luminescent intensities. The increased O2 ambient (1 Torr) resulted in a higher CL intensity compared to the thin films ablated in vacuum. The thin film ablated in Ar gas showed a much higher CL intensity than the other thin films. Ablation at a high fluence resulted in a higher CL intensity. The higher substrate temperature resulted in better CL intensities. The more spherically shaped particles and rougher surface led to increase CL intensities.

The effect of oxygen pressure on the structure, morphology and photoluminescence intensity of pulsed laser deposited Gd2O2S:Tb3+ thin film phosphor

Luminescent Gd2O2S:Tb3+ phosphor thin films were grown on Si (100) substrates, using the pulsed laser deposition technique. The films were grown in 100 to 300 mTorr oxygen gas (O2) atmospheres when the substrate temperature was kept constant at 400 or 600°C. The effect of the O2 ambient on the structure and morphological properties of the films were analyzed using x-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. Spherical nanoparticles deposited on the Si (100) substrates were shown to crystallize in the hexagonal structure of Gd2O2S. The photoluminescence (PL) spectra of all the films were characterized by a stable green emission peak with a maximum at 545 nm. Improved PL intensity was observed from the films deposited at higher oxygen pressures and higher substrate temperatures. Particles sizes of the nanoparticles deposited under the different conditions varied between 19 and 36 nm for the different samples. Smaller and more densely packet particles were produces at the higher O2 pressures and the higher temperature.

Cathodoluminescence degradation of PLD thin films

The cathodoluminescence (CL) intensities of Y2SiO5:Ce3+, Gd2O2S:Tb3+ and SrAl2O4:Eu2+,Dy3+ phosphor thin films that were grown by pulsed laser deposition (PLD) were investigated for possible application in low voltage field emission displays (FEDs) and other infrastructure applications. Several process parameters (background gas, laser fluence, base pressure, substrate temperature, etc.) were changed during the deposition of the thin films. Atomic force microscopy (AFM) was used to determine the surface roughness and particle size of the different films. The layers consist of agglomerated nanoparticle structures. Samples with good light emission were selected for the electron degradation studies. Auger electron spectroscopy (AES) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of the thin films. AES and CL spectroscopy were done with 2 keV energy electrons. Measurements were done at 1×10−6 Torr oxygen pressure. The formation of different oxide layers during electron bombardment was confirmed with X-ray photoelectron spectroscopy (XPS). New non-luminescent layers that formed during electron bombardment were responsible for the degradation in light intensity. The adventitious C was removed from the surface in all three cases as volatile gas species, which is consistent with the electron stimulated surface chemical reaction (ESSCR) model. For Y2SiO5:Ce3+ a luminescent SiO2 layer formed during the electron bombardment. Gd2O3 and SrO thin films formed on the surfaces of Gd2O2S:Tb3+ and SrAl2O4:Eu2+,Dy3+, respectively, due to ESSCRs.

PL and EL Characteristics in Bi- and Rare Earth-Co-Doped (La1-XGaX)2O3 Phosphor Thin Films Prepared by Magnetron Sputtering

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