Phosphor Thin Films Research Articles

Preparation of Blue Emitting BaMgAl[sub 10]O[sub 17]:Eu[sup 2+] Thin-Film Phosphors by Pulsed Laser Deposition

BaMgAl 10 O 17 :Eu 2+ (BAM) phosphors in the form of thin films have not yet been realized by physical vapor deposition methodologies due to technical difficulties. We report here on the preparation of thin-film-type BAM phosphors using a pulsed laser deposition technique. The luminescent and structural properties of BAM thin-film phosphors were monitored as a function of key processing parameters such as oxygen partial pressure, deposition time, laser energy density, and the type of postdeposition treatments used. By optimizing these processing parameters, BAM thin films with large homogenous areas (∼ 150 mm 2 ) and an acceptable photoluminescence could be produced.

Crystalline-phase-dependent red emission behaviors of Gd2O3:Eu3+ thin-film phosphors

Gd2O3:Eu3+ luminescent thin films have been grown on Al2O3(0001) substrates using pulsed-laser deposition. The films grown at different deposition conditions showed different crystalline phases, surface morphologies and luminescent characteristics. Both cubic and monoclinic crystalline phases were observed for the Gd2O3:Eu3+ films, and the crystalline structure and the surface morphology of the films were highly dependent on the oxygen pressure and substrate temperature. The cubic system showed a higher luminescence than the monoclinic system. The luminescence characteristics were strongly influenced by not only the crystalline structure but also the surface morphology of the films. The photoluminescencebrightness data obtained from Gd2O3:Eu3+ films indicate that Al2O3(0001) is a promising substrate for growth of high-quality Gd2O3:Eu3+ thin-film red phosphor. In particular, the Gd2O3:Eu3+ films showed a much better photoluminescence behavior than a Y2O3:Eu3+ films with the same thickness.

Enhanced luminescence of Gd 2O 3:Eu 3+ buffer-layered Y 2O 3:Eu 3+ thin films

Y 2O 3:Eu 3+ thin films have been grown on Si (1 0 0) substrates using Gd 2O 3:Eu 3+ as a buffer layer to reduce the lattice mismatch by pulsed laser deposition. The crystallinity, surface morphology and photoluminescence of the films are highly dependent on the thickness of buffer layer. The photoluminescence results obtained from Y 2O 3:Eu 3+ films grown on the Gd 2O 3:Eu 3+ buffer layer under optimized conditions have indicated that reducing lattice mismatch is very important factor for the growth of high quality Y 2O 3:Eu 3+ thin film phosphor. In particular, the incorporation of Gd 2O 3:Eu 3+ buffer layer induced an improved crystallinity, surface roughness and an increase of photoluminescence. The highest emission intensity was observed Y 2O 3:Eu 3+ films with 121 nm Gd 2O 3:Eu 3+ buffer layer, whose brightness was a factor of 2.1 larger than that from Y 2O 3:Eu 3+ films without buffer layer.

Highly enhanced photoluminescence and X-ray excited luminescence of Li doped Gd 2O 3:Eu 3+ thin films

Transparent Li-doped Gd 2O 3:Eu 3+ thin-film phosphors were prepared by a modified sol–gel method. The effect of the Li + ions on luminescent properties of the thin film was investigated. The results indicated that incorporation of Li + ions into Gd 2O 3 lattice could result in a remarkable increase on photoluminescence or X-ray excited luminescence, and the strongest emission was observed from Gd 1.84Li 0.08Eu 0.08O 3− δ film, in which the intensity was increased by a factor of 1.9 or 2.3 in comparison with that of Gd 1.92Eu 0.08O 3 film. And it could be achieved the highest intensity for sintering the Gd 1.84Li 0.08Eu 0.08O 3− δ film at 700 °C. Such a temperature is much lower than the typical solid-state reaction temperature for its powder phosphors. This kind of transparent thin-film phosphors may promise for application to micro X-ray imaging system.

A novel hydrate-based thin-film phosphor: low-temperature growth process and properties

Thin films of barium chloride hydrate doped with cerium were deposited by spray pyrolysis of aqueous solutions. The cathodoluminescence (CL) spectrum consists of two peaks at 443 and 485 nm due to 4f–5d transitions of the cerium ion in thin films without post-heat treatment. The CL depended dramatically on deposition temperature between 250 °C and 500 °C. The phenomenon is directly related to the change of crystallinity and Cl concentration of the thin films. The CL spectra of thin films of BaCl2·2H2O:Ce were compared on various substrates. The relaxation behavior of CL was also observed in thin-film phosphor. Our results indicate that the material studied as thin-film phosphor is unique since it contains water. It seems that the 4f–5d transition in Ce is so energetic that the O–H phonons cannot disturb it, indicating that barium chloride hydrate is a novel host in which Ce has a higher efficiency.

High-Luminance EL Devices Using Zn2Si1-XGeXO4:Mn Thin Films Prepared by Combinatorial Deposition by r.f. Magnetron Sputtering with Subdivided Powder Targets

A new technique incorporating combinatorial deposition to develop thin-film phosphors by r.f. magnetron sputtering is demonstrated using subdivided powder targets. In comparison with development using conventional r.f. magnetron sputtering, the atomic ratios of Si and Ge as well as the Mn content in Zn 2 Si 1-X Ge X O 4 :Mn thin film phosphors could be more efficiently optimized in order to obtain the highest intensity in electroluminescent and photoluminescent emissions. High luminances of 11800 and 1536 cd/m 2 were obtained in Zn 2 Si 0.6 Ge 0.4 O 4 :Mn thin-film electroluminescent devices fabricated under optimized conditions and driven at 1 kHz and 60 Hz, respectively.

Photoluminescence characteristics of Se-doped ZnGa2O4:Mn2+ thin-film phosphors grown by pulsed laser deposition on Al2O3(0001) substrates

Se-doped ZnGa2O4:Mn2+ thin-film phosphors have been grown using a pulsed laser deposition technique at various growth conditions. Structural characterization was carried out on a series of Se-doped ZnGa2O4:Mn2+ films grown on Al2O3(0001) substrates using Zn-rich ceramic targets. The results of X-ray diffraction patterns showed that the lattice constants of the films decrease with the substitution of Se for the oxygen in the ZnGa2O4. Photoluminescence (PL) of Se-doped ZnGa2O4:Mn2+ thin films has indicated that Al2O3(0001) is a promising substrate for the growth of high-quality Se-doped ZnGa2O4:Mn2+ films. The emission spectra of Se-doped ZnGa2O4:Mn2+ films show a broad band extending from 479 to 550 nm and peaking at 508 nm. In particular, the incorporation of Se into the ZnGa2O4 lattice could induce an increase in the PL. The PL peak intensity of the Se-doped ZnGa2O4:Mn2+ films is a factor of 2.8 larger than that of the ZnGa2O4:Mn2+ films. This phosphor is promising for applications in flat-panel displays.

The effects of substrates and deposition parameters on the growing and luminescent properties of Y3Al5O12:Ce thin films

Abstract YAG:Ce (Ce doped Y 3 Al 5 O 12 ) phosphor thin films were deposited by rf magnetron sputtering on quartz and sapphire substrates. The effects of sputtering parameters, annealing conditions, and substrates on the crystallinity and the luminescent properties were investigated. Oxygen partial pressure in sputtering gas strongly contributed to the crystallinity and atomic ratio of Al/Y, and the luminescent properties of YAG:Ce films accordingly depended on it. Stoichiometric and polycrystalline YAG:Ce films could be obtained at the gas ratio of 50% oxygen. After annealing process, amorphous YAG:Ce films were not only transformed to crystalline phases, but also activated to exhibit the yellow emission peak at 550 nm with the excitation wavelength of 450 nm. The films deposited on c -plane sapphire substrates exhibited higher PL intensity than those on quartz substrates due to the superior crystallinity.

Crystallinity and morphology dependent luminescence of Li-doped Y2−xGdxO3:Eu3+ thin film phosphors

Abstract The influence of lithium doping on the crystallization, the surface morphology, and the luminescent properties of pulsed laser deposited Y 2− x Gd x O 3 :Eu 3+ thin film phosphors was investigated. The crystallinity, the surface morphology, and the photoluminescence (PL) of films depended highly on the Li-doping and the Gd content. The relationship between the crystalline and morphological structures and the luminescent properties was studied, and Li + doping was found to effectively enhance not only the crystallinity but also the luminescent brightness of Y 2− x Gd x O 3 :Eu 3+ thin films. In particular, the incorporation of Li and Gd into the Y 2 O 3 lattice could induce remarkable increase in the PL. The highest emission intensity was observed Li-doped Y 1.35 Gd 0.6 O 3 :Eu 3+ thin films whose brightness was increased by a factor of 4.6 in comparison with that of Li-doped Y 2 O 3 :Eu 3+ thin films.

Surface morphology and photoluminescence characteristics of Eu-doped YVO4 thin films

Abstract Surface morphology and crystallinity of YVO4:Eu3+ thin films have influenced on the photoluminescence characteristics. The YVO4:Eu3+ films have been deposited on Al2O3 (0 0 0 1) substrates using pulsed laser deposition method. The films were grown at the various substrate temperatures and oxygen pressures. The substrate temperatures were changed from 500 to 700 °C and the range of oxygen pressures was 100–400 mTorr. The crystallinity and surface morphology of the films were investigated using X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. The results of XRD showed that YVO4:Eu3+ films had zircon structure and AFM study revealed that the films consisted of homogeneous grains ranging from 100 to 400 nm depending on the deposition conditions. The photoluminescence spectra were measured at room temperature using a luminescence spectrometer and the emitted radiation was dominated by the red emission peak at 620 nm radiated from the transition of 5D0–7F2. The crystallinity, surface morphology and photoluminescence spectra of thin-film phosphors were highly dependent on the deposition conditions, in particular, the substrate temperature and oxygen pressure. The surface roughness and photoluminescence intensity of the films showed similar behavior as a function of substrate temperature and oxygen pressure.

Blue-violet phosphate phosphor thin films for EL

Photoluminescence (PL) and electroluminescence (EL) in blue-violet emission were observed in newly developed phosphate phosphor thin films such as Ba 3(PO 4) 2:Eu and Ba 3(PO 4) 2:Ti. These phosphate phosphor thin films were first deposited on thick BaTiO 3 ceramic sheets by r.f. magnetron sputtering using powder targets and then post-annealed in various atmospheres. Blue-violet PL and EL emissions were obtained in Ba 3(PO 4) 2:Eu and Ba 3(PO 4) 2:Ti phosphor thin films that were deposited in an Ar + H 2 (10%) gas atmosphere and then post-annealed above about 900 °C in an Ar + H 2 (10%) gas atmosphere. In particular, the EL observed in Ba 3(PO 4) 2:Eu thin films exhibited two peaks, a red emission peaking at about 615 nm and a blue-violet emission peaking at about 420 nm. A luminance of 2.0 cd/m 2 in blue-violet emission was obtained in a thin-film EL device using a two step post-annealed Ba 3(PO 4) 2:Eu thin-film emitting layer: step 1, post-annealing at 1000 °C in air for 1 h, and step 2, post-annealing at 1000 °C in an Ar + H 2 atmosphere.

Improving the cathodoluminescent properties of thin films of Y2O3:Eu by doping with zinc and laser annealing

The development of thin-film phosphors with good color and brightness characteristics is one of the most important aspects in improving the technology of field emission displays. This paper discusses how doping with zinc and laser annealing affects the properties of thin films of europium-doped yttrium oxide. It is shown that doping makes it possible to improve the purity of the luminescence color, while laser annealing substantially increases the cathodoluminescence intensity. © 2005 Optical Society of America

ZnO:Zn phosphor thin films prepared by face-to-face annealing

ZnO:Zn phosphor thin films were prepared by face-to-face annealing at 450 °C in air. The effects of the face-to-face annealing on the structural and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. Measurement results showed that the crystal quality of ZnO films was improved by face-to-face annealing. Both UV light emission and visible light emission were enhanced compared to those of open annealing films. The UV emission peak was observed to have a blueshift towards higher energy. The optical band-gap edge of as-annealed films shifted towards longer wavelength.

Growth and optical properties of nanocrystalline Gd 3Ga 5O 12:Ln [formula omitted] powders and thin films via Pechini sol–gel process

Rare earth (Eu 3+, Tb 3+, Er 3+)-doped gadolinium gallium garnet (Gd 3Ga 5O 12, GGG) nanocrystalline powder and thin film phosphors were prepared by the Pechini sol–gel process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) as well as photoluminescence (PL) spectra were used to characterize the resulting powder and film samples. Both the powders and the coatings crystallized completely at 800 °C. The dopant rare earth ions show their characteristic emissions in Gd 3Ga 5O 12 phosphors, i.e., 5D 0– 7F J ( J = 1 , 2 , 3 , 4 ) transitions for Eu 3+, 5D 4– 7F J ( J = 3 , 4 , 5 , 6 ) transitions for Tb 3+ and ( 2H 11/2– 4I 15/2, 4S 3/2– 4I 15/2) transitions for Er 3+, respectively. In addition, the near infrared emission spectra (NIR) and the near infrared to visible upconversion (anti-Stokes) luminescence of Er 3+ were also observed in the Er 3+-doped Gd 3Ga 5O 12 samples. Possible mechanism responsible for the upconversion luminescence of Er 3+ was proposed.

Combinatorial deposition of EL phosphor thin films by r.f. magnetron sputtering using a subdivided powder target

A new technique incorporating combinatorial deposition by r.f. magnetron sputtering was used to develop new Eu-activated multicomponent oxynitride thin-film phosphors for electroluminescence. By sputtering with a powder target that is subdivided into two parts, phosphor thin films with a chemical composition that varied across the substrate surface could be successfully prepared. Thin-film electroluminescent (TFEL) devices were fabricated incorporating various Eu-activated phosphor host materials such as multicomponent oxynitrides: GaN, AlN or Si 3N 4 combined with Ga 2O 3, CaO or ZnO. In ((AlN) 1− X –(CaO) X ):Eu thin films, for example, the chemical composition (CaO content ( X)) could be optimized to obtain higher electroluminescent and photoluminescent emission intensities by using only one deposition with the new technique. As a result, a luminance of 170 cd/m 2 for red emission was obtained in an ((AlN) 0.1–(CaO) 0.9):Eu TFEL device driven at 1 kHz. High luminances were also obtained in red-emitting-TFEL devices using either a ((GaN) 0.9–(Ga 2O 3) 0.1):Eu or a ((GaN) 0.8–(ZnO) 0.2):Eu thin film prepared with an optimized composition.

Luminescence of Pulsed-Laser-Deposited SrAl2O4 : Eu ,Dy Thin Film and Its Role as a Stress Indicator

The ultimate goal of the present investigation was to develop an ,Dy thin-film phosphor on the surface of mechanical test specimens to act as a stress or crack indicator during testing. As a preliminary step, ,Dy thin-film phosphors were deposited on several conventional substrates such as quartz glass, Si(111), Si(001), and corrugated quartz glass using a pulsed laser deposition (PLD) technique. Processing parameters were optimized, in an attempt to enhance the efficiency of luminescence of the ,Dy thin-film phosphor. The optimal PLD processing conditions for the ,Dy thin-film phosphor were different from that for other conventional oxide thin-film phosphors in that an oxygen supply during the PLD process was not necessary, a postdeposition annealing in an oxidizing atmosphere was ineffective, and the corrugated substrate did not have a significantly enhanced extraction efficiency. By adopting the best PLD processing conditions, based on the preliminary depositions on conventional substrates, the ,Dy thin-film phosphor was deposited on the surface of a compact tension specimen composed of polycrystalline and the applicability of the ,Dy thin-film phosphor as a stress or crack indicator was verified in an actual mechanical test.

Growing Behavior and Luminescent Properties of Y3Al5O12:Ce Phosphor Thin Films grown by rf Magnetron Sputtering

Trivalent cerium<TEX>$(Ce^{3+})$</TEX> activated YAG (yttrium aluminum garnet, <TEX>$Y_3Al_5O_{12})$</TEX>) thin films phosphor were deposited on quartz glass substrates by rf magnetron sputtering. The effects of sputtering parameters, annealing atmosphere, and substrates on growing behaviors and luminescent properties were investigated. The sputtering parameters were <TEX>$O_2/(Ar+O_2)$</TEX> gas ratio, rf power, and deposition time. XRD (X-ray diffractometery) spectra exhibited that as-deposited films were amorphous, while they were transformed to the crystalline phases by post-annealing. The crystallinity and the atomic ratio strongly depended on the sputtering gas ratio <TEX>$O_2/(Ar+O_2)$</TEX>. High quality YAG:Ce thin films could be obtained at the gas ratio of <TEX>$50\%$</TEX> oxygen. After annealing process, PL (Photoluminescence) spectra excited at 450nm showed a yellow single band at 550nm. The films deposited at the sputtering gas ratio of 50% oxygen exhibited the highest PL intensity.

Photoluminescence behavior of Eu3+ activated Sr2SiO4 thin-film phosphors grown by pulsed-laser deposition

Sr2SiO4:Eu3+ thin films have been grown on Al2O3 (0001) substrates using pulsed-laser deposition. The Sr2SiO4:Eu3+ thin films were grown at various oxygen pressures and substrate temperatures. The crystallinity and surface morphology of the films were investigated using x-ray diffraction and atomic-force microscopy. The crystallinity and surface roughness of the films are highly dependent on the deposition conditions. The photoluminescence spectra were measured at room temperature using a luminescence spectrometer and excitation by a broadband incoherent ultraviolet-light source with a dominant-excitation wavelength of 254 nm. Measurements of photoluminescence properties of Sr2SiO4:Eu3+ thin films have indicated that Al2O3 (0001) is a promising substrate for the growth of high-quality Sr2SiO4:Eu3+ films. The photoluminescence (PL) spectra exhibit a broadband emission extending from 565 to 670 nm and appear to be composed of several overlapping emission bands. The PL peaks are located at 582, 597, and 620 nm and the PL intensity increases with increasing oxygen pressure and reaches a maximum at 150 mTorr. This phosphor is promising for applications in flat-panel displays.

Effect of the extinction coefficient on the extraction efficiency of ZnS:Mn thin-film phosphors grown on two-dimensional nanorod substrates

We have studied the effects of varying the extinction coefficient of two-dimensional (2D) nanorod-assisted ZnS:Mn thin-film phosphors on their photoluminescence extraction efficiency. The finite-difference time-domain method was employed for the design and analysis of 2D nanorod-assisted thin-film phosphors. Using a nanorod pattern with a depth of 200 nm, a lattice constant of 600 nm, and a radius of 180 nm, the extraction efficiency of a transparent ZnS:Mn thin-film phosphor is predicted theoretically to increase by a factor of more than ∼9.1. Experiments have shown that incorporation of the 2D SiO2 nanorod layer only improves the light extraction efficiency over that of a conventional ZnS:Mn thin-film phosphor by a factor of ∼4.0. We discuss the reasons for this mismatch between the theoretical and experimental extraction efficiencies, in order to further improve the extraction efficiency of ZnS-based thin-film phosphors.

Photoluminescence behaviors of Eu-doped GdVO 4 thin film phosphors grown by pulsed laser ablation

GdVO 4:Eu 3+ thin films have been grown on Si (1 0 0) substrates using pulsed laser deposition. The films deposited at the different conditions show different microstructural and luminescent characteristics. The crystallinity, surface morphology and photoluminescence of the films are highly dependent on the deposition conditions, oxygen pressure and substrate temperature. The photoluminescence results obtained from GdVO 4:Eu 3+ films grown under optimized conditions have indicated that Si (1 0 0) is promising substrate for the growth of high quality GdVO 4:Eu 3+ film phosphor. In particular, the surface morphology and photoluminescence of GdVO 4:Eu 3+ films show very similar behavior as a function of oxygen pressure. The emitted radiation was dominated by the red emission peak at 620 nm and this phosphor is promising for applications in flat panel displays.