Phosphor Thin Films Research Articles

Oxide thin-film electroluminescent devices and materials

This report reviews newly developed oxide phosphors shown to be promising as the emitting layer of thin-film electroluminescent (TFEL) devices. Since the first report of a high-luminance TFEL device using a Mn-activated Zn 2SiO 4 (Zn 2SiO 4:Mn) phosphor, high-luminance multicolor-emitting TFEL devices have been fabricated using various oxide phosphors activated with Eu or Mn. In addition, many oxides that consist of binary and ternary compounds and multicomponent oxides have been developed and shown to be promising as a host material for TFEL phosphors. This report focuses on Mn-activated Y 2O 3-based oxide phosphors: a binary compound and various ternary compounds and multicomponent oxides, composed of Y 2O 3 in combination with another binary compound such as Ga 2O 3 or GeO 2. TFEL devices of which every constituent was an oxide material were fabricated using oxide phosphor thin films deposited by r.f. magnetron sputtering, pulsed laser deposition or a sol–gel process. High luminances and luminous efficiencies comparable to those of TFEL devices using ZnS:Mn sulfide phosphor were realized using Mn-activated Y 2O 3-based oxide phosphors. Luminances above 7000 cd/m 2 (1 kHz-driving voltage) and luminous efficiencies of approximately 10 lm/W (60 Hz driving voltage) were obtained in yellow emitting TFEL devices fabricated using a Y 2O 3:Mn, a ((Y 2O 3) 0.6–(GeO 2) 0.4):Mn or a ((Y 2O 3) 0.5–(Ga 2O 3) 0.5):Mn thin film and driven by an ac sinusoidal wave voltage. Also, a high luminance above 1000 cd/m 2 for green emission was obtained in a ((Y 2O 3) 0.3–(Ga 2O 3) 0.7):Mn TFEL device driven at 1 kHz.

Electroluminescent ZnS–Cu films made by metal–organic chemical vapour deposition and thermodiffusion

ZnS, ZnS–Cu films were deposited using an original chemical method under atmospheric pressure on to glass substrates to form thin-film electroluminescent (TFEL) devices. The ZnS, ZnS–Cu films were doped with Cu, Cl by a thermodiffusion (thermal diffusion) method from a ZnS powder doped with Cu and Cl. The TFEL devices had a conventional double insulating structure. The investigated TFEL devices had performance parameters including blue colour emission (λmax = 455 nm) and a brightness of 10 cd m−2 under sine wave excitation at a voltage of 60 V and a frequency of 5 kHz. The composition of the spectra was studied and from these results it was shown that the relative intensity of the bands and the maximum location are determined from the growth conditions. There are two main types of electroluminescent (EL) spectra, which differ in the number and location of green emission bands. A set of conditions was found for the fabrication of stable ZnS–Cu, Cl devices. The degradation behaviour of the ZnS–Cu, Cl device fabricated using the new method is the same as that of a commercial thin-film phosphor. The possibility of obtaining a stable ZnS–Cu emitter is shown. The EL mechanism and degradation characteristics are discussed.

Photoluminescence behavior of pulsed laser deposited ZnGa 2 O 4 thin-film phosphors grown on various substrates

ZnGa2O4 thin-film phosphors have been grown on Si(100), Al2O3(0001) and MgO(100) substrates using pulsed laser deposition. The structural characterization was carried out on a series of ZnGa2O4 films grown on various substrates under various substrate temperatures and oxygen pressures. The films grown on these substrates not only have different crystallinity and surface morphology, but also different Zn/Ga composition ratio. The crystallinity and photoluminescence (PL) of the ZnGa2O4 films are highly dependent on the deposition conditions, in particular the stoichiometry ratio of Zn/Ga and the kind of substrate. The variation of Zn/Ga in the films also depends on not only the oxygen pressure but also the substrate temperature during deposition. The PL properties of pulsed laser deposited ZnGa2O4 thin films have indicated that Al2O3(0001) and MgO(100) are promising substrates for the growth of high-quality ZnGa2O4 thin films and that the luminescence brightness depends on the substrate. The luminescence spectra show a broad band extending from 350 to 600 nm and peaking at 460 nm.

Dependence of structural and luminescent characteristics of Y2O3:Er thin film phosphors on substrate

The dependence of the structural and cathodoluminescent (CL) characteristics of green-emitting Y2O3:Er thin films phosphors deposited by electron beam evaporation on substrate used for the Y2O3:Er thin film deposition has been investigated. Quartz glass, ITO glass and c-axis-oriented ZnO thin film substrates were used as the substrate. Best crystallinity and CL luminance were obtained from the Y2O3:Er thin film deposited on the ZnO thin film substrate. One of the reason for this fact might be due to high conductivity the substrate. The other might be due to better crystallinity of Y2O3:Er thin film deposited on the ZnO thin film substrate than that on the quartz and ITO substrates, because of the best crystallinity of the ZnO thin film substrate among three substrates. The Y2O3:Er thin film deposited at 500°C on the ZnO thin film and annealed at 800°C for 1h in O2 flow showed CL luminance of 70cd/m2 with pure green emission under excitation by electron beam with 3kV, 60μA/cm2.

Preparation of Mn-activated yttrium germanate phosphor thin films for electroluminescent devices

Manganese (Mn)-activated yttrium germanate phosphor thin films were prepared by conventional r.f. magnetron sputtering. The phosphor thin films prepared with a Y 2O 3 content of 33, 50 and 67 mol.% and postannealed above approximately 950 °C were crystallized and identified as Y 2Ge 2O 7, Y 2GeO 5 and Y 4GeO 8, respectively, whereas all as-deposited thin films were found to be amorphous. Thin-film electroluminescent (TFEL) devices were fabricated using the postannealed phosphor thin films. The obtainable electroluminescent (EL) characteristics were considerably affected by the Mn content and the postannealing temperature of the phosphor thin-film emitting layers. High luminances for yellow photoluminescence and EL emissions were obtained in TFEL devices using these ternary compound phosphors activated with Mn and postannealed at 1020–1045 °C. Maximum luminance of 2590, 3020 and 2500 cd/m 2 were obtained in 1 kHz-driven TFEL devices using Y 2Ge 2O 7:Mn, Y 2GeO 5:Mn and Y 4GeO 8:Mn thin-film emitting layers, respectively.

Photoluminescence characteristics of Li-doped Y2O3:Eu3+ thin-film phosphors onsapphire substrates

Y2O3:Eu3+ and Li-doped Y2O3:Eu3+ luminescent thin films have beengrown on sapphire substrates using a pulsed laser deposition technique.The thin-film phosphors were deposited at a substrate temperature of600°C under the oxygen pressures of 100, 200, and 300 mTorr. The filmsgrown under different deposition conditions have been characterized usingmicrostructural and luminescence measurements. The crystallinity andphotoluminescence (PL) of the films are highly dependent on the oxygenpressure. The PL brightness data obtained from Y2O3:Eu3+ films grownunder optimized conditions have indicated that sapphire is a promisingsubstrate for the growth of high-quality Y2O3:Eu3+ thin-film red phosphor. Inparticular, the incorporation of Li+ ions into Y2O3 lattice could induce aremarkable increase of PL. The highest emission intensity was observedwith LiF-doped Y1.84Li0.08Eu0.08O3 (Y2O3LiEu), whose brightness wasincreased by a factor of 2.7 in comparison with that of Y2O3:Eu3+ films.This phosphor may hold promise for application in flat-panel displays.

Photoluminescence behaviors in ZnGa 2O 4 thin film phosphors deposited by a pulsed laser ablation

ZnGa 2O 4 thin film phosphors have been deposited using a pulsed laser deposition technique on Si (1 0 0) and Al 2O 3 (0 0 0 1) substrates at a substrate temperature of 550 °C with various oxygen pressures 100, 200 and 300 mTorr, and various substrate temperatures of 450, 550 and 650 °C with a fixed oxygen pressure of 100 mTorr. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. Under the different substrate temperatures, ZnGa 2O 4 thin films show the different crystallinity and luminescent intensity. The crystallinity and photoluminescence (PL) of the ZnGa 2O 4 films are highly dependent on the deposition conditions, in particular, oxygen pressure, substrate temperature, a kind of substrates. The luminescent spectra show a broad band extending from 350 to 600 nm peaking at 460 nm. The PL brightness data obtained from the ZnGa 2O 4 films grown under optimized conditions have indicated that the sapphire is one of the most promised substrates for the growth of high quality ZnGa 2O 4 thin film phosphor.

Electron Beam Induced Degradation of CaS:Pb Thin Film Phosphor Grown by Atomic Layer Deposition

The effects of electron (e)-beam irradiation on the luminescent and the materials properties of CaS:Pb films were investigated using structural and compositional analysis techniques. Continuous e-beam irradiation on CaS:Pb thin film for 180 min resulted in an approximately 60% decrease of cathodoluminescence (CL) intensity. Transmission electron microscopic analysis indicated that e-beam irradiation induced the precipitation of Pb. The decrease of CL intensity by e-beam irradiation was mostly caused by the decrease of Pb 2 + luminescent center ion concentration due to the precipitation of Pb. E-beam irradiation also resulted in heavy carbonaceous contamination on the surface. The thickness of the carbonaceous layer was approximately 10 nm.

Doping Effects on Electrical and Luminescent Properties of Zinc Oxide-Based Nanocomposite Red Phosphor Thin Films

Doping Effects on Electrical and Luminescent Properties of Zinc Oxide-Based Nanocomposite Red Phosphor Thin Films

Photoluminescence of Li-doped Y2O3:Eu3+thin film phosphors grown by pulsed laser deposition

<TEX>$Y_2O_3:Eu^{3+}$</TEX> and Li-doped <TEX>$Y_2O_3:Eu^{3+}$</TEX> thin films have been grown on sapphire substrates using a pulsed laser deposition technique. The thin film phosphors were deposited at a substrate temperature of <TEX>$600^{\circ}C$</TEX> under the oxygen pressure of 100, 200 and 300 mTorr. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The crystallinity and photoluminescence (PL) of the films are highly dependent on the oxygen pressure. The PL brightness data obtained from <TEX>$Y_2O_3:Eu^{3+}$</TEX> films grown under optimized conditions have indicated that sapphire is one of the most promising substrate for the growth of high quality <TEX>$Y_2O_3:Eu^{3+}$</TEX> thin film red phosphor. In particular, the incorporation of <TEX>$Li^{+}$</TEX> ions into <TEX>$Y_2O_3$</TEX> lattice could induce a remarkable increase of PL. The highest emission intensity was observed with LiF-doped <TEX>$Y_{1.84}Li_{0.08}Eu_{0.08}O_3(Y_2O_3LiEu)$</TEX>, whose brightness was increased by a factor of 2.7 in comparison with that of <TEX>$Y_2O_3:Eu^{3+}$</TEX> films. This phosphor may promise for application to the flat panel displays.

Luminescence characteristics of pulsed laser deposited ZnGa 2O 4 thin film phosphors grown on various substrates

ZnGa 2O 4 thin film phosphors have been grown on Si (1 0 0), Al 2O 3 (0 0 0 1) and MgO (1 0 0) substrates using pulsed laser deposition. The structural characterization was carried out on a series of ZnGa 2O 4 films grown on various substrates under fixed substrate temperature and oxygen pressure 550°C and 100 mTorr, respectively. The films grown on these substrates not only have different crystallinity and surface morphology, but also the Zn/Ga composition ratio. The photoluminescence properties of pulsed laser deposited ZnGa 2O 4 thin films have indicated that Al 2O 3 (0 0 0 1) and MgO (1 0 0) are promising substrates for the growth of high quality ZnGa 2O 4 thin films and luminescence brightness depends on the substrate. The luminescent spectra show a broad band extending from 350 to 600 nm and peaking at 460 nm.

Blue cathodoluminescence from Ba2B5O9Cl:Eu phosphor thin films on glass substrates

Spray pyrolysis was used to deposit thin films of Ba2B5O9Cl:Eu from aqueous solutions containing Eu3+. Blue cathodoluminescence due to the abnormal reduction of Eu3+→Eu2+ in as-grown thin films was observed at the growth temperatures from 140 °C to 500 °C. Significant line narrowing was found as the growth temperature increased. Using either conventional or rapid thermal annealing of thin films in air enhanced the transition of the emission spectrum from several peaks to a sharp single peak. Our results also provide the possibility of tuning the blue emission at temperatures suitable for the use of glass substrates in flat panel applications.

Luminescent properties of rare-earth ion doped yttrium silicate thin film phosphors for a full-colour display

In this paper, we report our results on the sol–gel preparation and spectral properties of (RExY1−x)2SiO5 (RE3+ = Eu3+, Tb3+, Ce3+, x = 0.005, 0.01, 0.02, 0.03 and 0.05) thin films. Effects of annealing temperatures on the thin films structure and optical properties, including luminescence, decay kinetics and CIE colour coordinates have been investigated. Upon exposure to the UV source, films containing Eu3+ and Tb3+ have exhibited bright red- and green-phosphorescent colours, due to the prominent transitions of 5D0→7F2 at 613 nm of Eu3+ and 5D4→7F5 at 543 nm of Tb3+ arising because of the intra-4f n electronic transitions, respectively. The photoluminescence spectrum of (CexY1−x)2SiO5 film mainly shows a broader emission band at 488 nm, which originates from the 5d→4f electron transitions of Ce3+. Luminescence mechanisms of these phosphor thin films have been discussed in detail.

Enhanced luminescence of pulsed-laser-deposited Y2O3:Eu3+ thin-film phosphors by Li doping

Y 2 O 3 : Eu 3+ and Li-doped Y2O3:Eu3+ luminescent thin films have been grown on sapphire substrates using pulsed-laser deposition. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The photoluminescence (PL) brightness data obtained from Li-doped Y2O3:Eu3+ films grown under optimized conditions have indicated that sapphire is a promising substrate for the growth of high-quality Li-doped Y2O3:Eu3+ thin-film red phosphor. In particular, the incorporation of Li+ ions into Y2O3 lattice could induce a remarkable increase of PL. The highest emission intensity was observed with LiF-doped Y1.84Li0.08Eu0.08O3, whose brightness was increased by a factor of 2.7 in comparison with that of Y2O3:Eu3+ films. This phosphor may promise for application to the flat panel displays.

Luminescence of pulsed laser deposited Gd2O3:Eu3+ thin film phosphors on quartz glass substrates

Thin film phosphors of Gd2O3:Eu3+ were deposited on quartz glass plates by pulsed laser deposition and compared with typically used thin film phosphors composed of Y2O3:Eu3+ in terms of cathodoluminescence (CL) and photoluminescence (PL). Both the CL and PL of Gd2O3:Eu3+ thin film phosphor were superior to those of corresponding data on currently widely used Y2O3:Eu3+ red thin film phosphor. In particular, the Gd2O3:Eu3+ thin film phosphor showed a much better cathodoluminescence at low excitation energy (less than 1 keV) than a Y2O3:Eu3+ film of the same thickness, indicating that the Gd2O3:Eu3+ thin film phosphor is a much better candidate for use in field emission displays.

Sol–gel derived zinc silicate phosphor films for full-color display applications

Zn 2SiO 4 phosphor thin films doped with rare-earth ions including Tb 3+, Eu 3+ and Ce 3+ have been prepared using a wet chemistry sol–gel process. Optical properties and microstructure of these films were reported and discussed. Thin films containing Tb 3+ and Eu 3+ have shown bright green- and red-phosphorescent colors upon exposure to the UV source, due to the sharp and strong intra-4f n -shell electronic transitions of Tb 3+ ( 5D 4→ 7F 5) and Eu 3+ ( 5D 0→ 7F 2), respectively. Meanwhile, the photoluminescence of Zn 2SiO 4/Ce 3+ thin film mainly shows a broad band in the visible region peaked at around 489 nm, which results from 5d→4f electron transition of Ce 3+. The thermogravimetric analysis curve shows a remarkable weight loss in the temperature range of 50–450 °C, and slow loss continuing at higher temperature above 800 °C. The increase in fluorescence and decay lifetimes of rare-earth ions sensitive to films microstructure and chemical components corresponding to this weight loss are attributed to nanometer polycrystallites formation and OH removal by treatment of temperature.

Conductive Thin-Film Phosphors Prepared by a Sol-Gel Method

Conductive Thin-Film Phosphors Prepared by a Sol-Gel Method

Influence of Preparation Conditions on the Structural and Luminescent Properties of Blue-Emitting SrGa2 S 4 : Ce Thin-Film Phosphors

Blue-emitting ternary strontium thiogallate doped with Ce thin-film phosphor has been prepared by a multisource deposition technique by employing Sr, and as the source materials. The as-deposited films show a growth of single-phase polycrystalline strontium thiogallate with poor crystallinity. Various preparation conditions such as annealing temperatures, times, and Ce concentrations have been studied with respect to structural and luminescent properties of thin films. The film annealed at elevated temperature shows an increase in crystallinity of the which leads to dissociation to SrS on the surface. The photoluminescence spectra show a typical blue emission at 445 nm independent of annealing temperatures, whereas the cathodoluminescence spectra show blue emission at 800°C and a very broad band green emission peaked at 540 nm at 900°C. The results are discussed on the basis of formation of thiogallate, stability at high temperature, luminescent properties as a function of temperature, annealing atmosphere, and Ce concentrations. © 2002 The Electrochemical Society. All rights reserved.

Cathodoluminescence properties of blue-emitting SrGa2S4:Ce thin-films grown by low-temperature process

The cathodoluminescence (CL) properties of Ce-activated strontium thiogallate (SrGa2S4:Ce) thin films have been investigated aiming towards phosphor screen application in an emissive display under low to medium accelerating voltage (&amp;lt;5 kV) excitation. The SrGa2S4:Ce thin films were grown by multisource deposition using a molecular beam epitaxy system. The growth temperature of the CL phosphor thin films was 472.5 °C, which is the lowest value ever achieved. Several related properties were observed, including the CL spectra, luminance, luminous efficacy, and surface morphology of the thin films. A luminance of 1000 cd/m2 and an efficacy of 1 lm/W were obtained at an accelerating voltage of 5 kV with a current density of 60 μA/cm2. The light-outcoupling efficiency (ηout) of the film was 0.0531. In spite of this small ηout of the films compared to that of powder phosphors, the luminance and efficacy were comparable to the conventional ZnS:Ag, Cl powder phosphor. The average grain size of the films was 0.14 μm×0.04 μm. The high luminance and luminous efficacy of the films with their submicron grain size is useful to realize high-resolution emissive displays.

Luminescence characteristics of ZnGa 2O 4 thin film phosphors grown by pulsed laser deposition

ZnGa 2O 4 thin film phosphors have been deposited using a pulsed laser deposition technique on Si(100) substrates at a substrate temperature of 550 °C with various oxygen pressures and post-annealing temperatures. The structural characterization was carried out on a series of ZnGa 2O 4 films grown at an oxygen pressure range of 50–300 mTorr, and subsequently post-annealed at 600 and 700 °C. The optimum oxygen pressure for luminescent characteristics was about 100 mTorr. The luminescent spectra show a broad band extending from 350 to 600 nm peaking at 460 nm. A post-annealing treatment of ZnGa 2O 4 thin films led to the different shape of luminescent intensity and grain size. β-Ga 2O 3 phase appeared at an annealing temperature of 600 °C and increased with increasing annealing temperature. We have also investigated the effect of the ligand field strength on the resultant energy levels for ZnGa 2O 4 thin film phosphor. The annealing process at different temperatures may lead to different dominant emissions.