Phosphor Thin Films Research Articles

Enhanced luminescence in ZnGa2O4-xSx:Mn2+ thin-film phosphors grown on MgO(100) substrate

Mn-doped ZnGa2O4-xSx thin-film phosphors have been grown using a pulsed laser deposition technique at varying growth conditions. Structural characterization was carried out on a series of ZnGa2O4-xSx:Mn2+ films grown on MgO(100) substrates using Zn-rich ceramic targets. Oxygen pressure was fixed at 100 mTorr and substrate temperatures were varied from 500 to 700 °C. The results of X-ray-diffraction patterns showed that the lattice constants of the ZnGa2O3.95S0.05:Mn2+ thin films decrease with the substitution of sulfur for the oxygen in ZnGa2O4. Measurements of photoluminescence (PL) properties of ZnGa2O4-xSx:Mn2+ thin films have indicated that MgO(100) is one of the most promising substrates for the growth of high-quality ZnGa2O4-xSx:Mn2+ thin films. In particular, the incorporation of sulfur into the ZnGa2O4 lattice could induce a remarkable increase of PL. The highest green-emission intensity was observed with ZnGa2O3.95S0.05:Mn2+ films, whose brightness was increased by a factor of 3.5 in comparison with that of ZnGa2O4:Mn2+ films. This phosphor may be promising for application to flat-panel displays.

Enhancement of cathodoluminescence of ZnGa2O4:Mn thin-film phosphor by energetic particle bombardment

Enhancement of cathodoluminescence of manganese-activated zinc gallate (ZnGa2O4:Mn) thin-film phosphor by energetic particle bombardment is reported. The ZnGa2O4:Mn thin-film phosphor was grown at room temperature on silicon (100) substrates by rf magnetron sputter deposition from a 2 mol % Mn-doped ZnGa2O4 target in an oxygen–argon mixture. After the deposition, the films were annealed at 800 °C for 3 h in air. The influence of energetic particle bombardment on cathodoluminescent (CL) properties of ZnGa2O4:Mn films was investigated by varying a gas pressure during the sputter growth. Our results have shown that CL brightness from ZnGa2O4:Mn films grown at 2 mTorr was more than eight times higher than that of films grown at 20 mTorr. The remarkable improvement in CL brightness from ZnGa2O4:Mn films grown at a low pressure is presumably due to the energetic particle bombardment of the growing film surface yielding a densely packed microstructure and a better crystalline quality with a highly [110]-textured structure.

Morphology-dependent luminescence behavior of Y2-xGdxO3:Eu3+ thin-film phosphors grown by a laser ablation

Y2-xGdxO3:Eu3+ luminescent thin films have been grown on Al2O3(0001) substrates using pulsed laser deposition. Films grown under different deposition conditions have been characterized using microstructural and luminescence measurements. The crystallinity, surface morphology and photoluminescence (PL) of the films are highly dependent on the amount of Gd present. The photoluminescence (PL) brightness data obtained from Y2-xGdxO3:Eu3+ films grown under optimized conditions have indicated that Al2O3(0001) is one of the most promising substrates for the growth of high-quality Y2-xGdxO3:Eu3+ thin-film red phosphors. In particular, the incorporation of Gd into the Y2O3 lattice could induce a remarkable increase of PL. The highest emission intensity was observed with Y1.35Gd0.60Eu0.05O3, whose brightness was increased by a factor of 3.1 in comparison with that of Y2O3:Eu3+ films. This phosphor may be promising for application in flat-panel displays.

Cathodoluminescence of rare-earth-doped zinc aluminate films

Eu-, Tb-, and Tm-doped zinc aluminate (ZnAl 2O 4) thin film phosphors were prepared by the spray pyrolysis technique at an ambient pressure. The effects of preparation conditions on the cathodoluminescence properties of the films were studied. Films containing Tb 3+ and Tm 3+ ions exhibited green and blue cathodoluminescence, respectively. For films doped with europium, both red emission lines from Eu 3+ and a broad blue–green emission band from Eu 2+ were observed. The CIE (Commission Internationale de L'Eclairage) chromatic coordinates, dominant wavelength, and color purity were determined for each phosphor. The luminance and efficiency of these phosphors at a current density of 57 μA/cm 2 are found to be linearly dependent on the excitation voltage.

Photoluminescence characteristics of pulsed laser deposited Y 2− xGd xO 3:Eu 3+ thin film phosphors

Y 2− x Gd x O 3:Eu 3+ phosphor thin films were grown on Si (1 0 0) and Al 2O 3 (0 0 0 1) substrates using a pulsed laser deposition (PLD) technique. Thin film phosphors were deposited by changing the substrates and the processing conditions (substrate temperature and oxygen pressure). The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The photoluminescence (PL) brightness data obtained from the Y 2− x Gd x O 3:Eu 3+ films grown under optimized conditions have indicated that Al 2O 3 (0 0 0 1) and Si (1 0 0) substrates are promising substrate for the growth of high quality Y 2− x Gd x O 3:Eu 3+ thin film red phosphor. The films were preferentially (2 2 2) oriented in both Si (1 0 0) and Al 2O 3 (0 0 0 1) cases and the films grown on Al 2O 3 (0 0 0 1) substrate exhibit the superior crystallization and photoluminescent properties. The highest emission intensity was observed with Y 1.35Gd 0.6O 3:Eu 3+ films grown on Al 2O 3 (0 0 0 1) substrate, whose brightness increased by a factor of 3.7 in comparison with that of the films grown on Si (1 0 0) substrate. The PL intensity of the Y 2− x Gd x O 3:Eu 3+ films are highly dependent on the crystallinity and surface roughness of the films. The PL intensity and surface roughness have similar behavior as a function of not only oxygen pressure but also substrate temperature. This phosphor may be promising for application to the flat panel displays.

Enhanced luminescence of Gd2O3:Eu3+ thin-film phosphors by Li doping

Gd 2 O 3 : Eu 3+ and Li-doped Gd2O3:Eu3+ luminescent thin films have been grown on Al2O3 (0001) substrates using pulsed-laser deposition. The films grown under different deposition conditions show different microstructural and luminescent characteristics. Both cubic and monoclinic crystalline structures were observed in Gd2O3:Eu3+ films, but only the cubic crystalline structure was observed for Li-doped Gd2O3:Eu3+ films grown under certain condition. The photoluminescence (PL) brightness data obtained from Li-doped Gd2O3:Eu3+ films indicate that sapphire is a promising substrate for growth of high-quality Li-doped Gd2O3:Eu3+ thin-film red phosphor. In particular, incorporation of Li+ ions into the Gd2O3 lattice can induce a remarkable increase of PL. The highest emission intensity was observed with LiF-doped Gd1.84Li0.08Eu0.08O3, whose brightness was a factor of 2.3 larger than that from Gd2O3:Eu3+ films. This phosphor is promising for applications in flat-panel displays.

Effects of substrates and heat treatment on growing behavior and luminescent characteristics of ZnGa2O4:Mn thin film

ZnGa2O4:Mn phosphor thin films were deposited on ZnO:Ga/glass, ZnO:Al/glass, ZnO/ITO/glass, and ITO/glass by rf magnetron sputtering. Effects of substrates and heat treatment on the structural and luminescent properties were investigated. The surface morphology, growing behavior, and luminescent properties of thin films depend on the crystallinity of the substrates. Thin film phosphors were heat-treated in a N2+vacuum, vacuum (∼10−3 Torr), and air atmosphere, respectively. The annealing conditions did not affect the surface morphology and crystallinity of the films. However, the Ga/Zn atomic ratios and luminescent characteristics were dependent on these conditions.

Luminescence characteristics of SrTiO 3:Pr,Ga phosphor synthesized by sol–gel process

The thin film phosphors of SrTiO 3:(0.004 mol Pr, 0.02 mol Ga) have been prepared by chemical solution deposition (CSD) method on the SiO 2/Si, alumina, and quartz substrates. The phase formation and photoluminescence (PL) property of thin films with crystallization temperature have been characterized by FE-SEM, XRD, and spectrophotometer. The SrTiO 3 (ST) phase was formed from 600 °C regardless of the type of substrate. The emission peak (611 nm) and excitation peak (370 nm) from the thin films were similar to those of the powder sample prepared by solid-state reaction. The SiO 2/Si substrate produced the strongest emission and excitation spectra.

Fabrication and characterization of a monolithic thin-film edge emitter device with zinc–oxide–tungsten-based thin-film phosphor

Advanced applications, such as space and geophysical exploration, medical and military applications, transportation and communications industries, and the goal of hang-on-the-wall television and computer monitors, have driven display technology toward a rapid advancement and development of the flat panel display (FPD) industry. Displays based on the principles of field emission have been regarded as a technology with a potential of replacing cathode ray tubes (CRTs) and liquid crystal displays. A field-emission display (FED) combines the best performance of a CRT in a configuration of a FPD because a FED offers high-power efficiency, high brightness and resolution, wide viewing angles, light weight, tolerance to temperature changes, and instant-on operation. However, commercial application of FEDs has been delayed because of the complex submicron processing involved in the fabrication of microtips for the cathode, early failure of cathodes due to sputter damage from uncontrolled emission current or current runoff, nonavailability of blue phosphors operating in low-voltage regimes, and lack of optimum sealing conditions. This article summarizes the development of a monochromatic monolithic thin-film edge emitter (MT-FEE) device while implementing a thin-film blue-light-emitting phosphor of zinc oxide and tungsten (ZnO:W). The device design reported here overcomes some of the above mentioned drawbacks of conventional FED designs. Performance of the MT-FEE devices was judged by controlling key parameters associated with the technology. Several test structures were fabricated by varying the dielectric, separating anode and cathode lines, in a range of 3–6 μm with emitter configurations as either saw-tooth or rectangular wedges to establish performance of the devices. Stable emission current of an approximate value of 200 nA per pixel was obtained at 300 V for 3 μm devices. Blue light was visible to the naked eye from several excited pixels in the 3 μm devices at voltages as low as 270 V.

PL and EL properties of Tm-activated vanadium oxide-based phosphor thin films

The preparation of high-luminance blue emitting Tm-activated multicomponent oxide phosphor thin films is described. The phosphor thin films were deposited on thick BaTiO 3 ceramic sheets by r.f. magnetron sputtering using powder targets. A very high photoluminescence (PL) intensity in blue emission could be observed in postannealed Tm-activated gadolinium oxide–vanadium oxide Gd 0.5–V 0.5–O:Tm thin films prepared using Tm 2O 3-doped (Gd 2O 3) 0.5–(V 2O 5) 0.5 targets (V 2O 5 content of 50 mol.%). It should be noted that thin films of this phosphor postannealed at 1100 °C in air exhibited higher PL intensity than those from commercially available blue BaMgAl 14O 23:Eu (BAM) phosphor powder and Gd 0.5–V 0.5–O:Tm powders. In addition, a Gd 0.5–V 0.5–O:Tm thin-film electroluminescent device exhibited a blue emission that was the same as the PL emission.

Oxide phosphor and dielectric thin films for electroluminescent devices

Since its inception in the early 1990s, the field of high brightness, high stability oxide phosphor electroluminescence (OPEL) continues to develop with efforts now underway in several groups around the world. Green-emitting phosphors Zn 2SiO 4:Mn, Zn 2Si 1− x Ge x O 4:Mn and ZnGa 2O 4:Mn achieve efficiencies of 0.5–2.5 lm/W. Lifetimes of 50 000 h in air are achieved, even without control of humidity. Red emission from Ga 2O 3:Eu and MgGa 2O 4:Eu has also been realized, with efficiencies approaching 1 lm/W. Recently, higher efficiencies of up to 10 lm/W have been reported in yellow emitting Y 2O 3:Mn and (Y 2O 3) x (GeO 2) y :Mn. Commercialization of OPEL for flat panel displays and lamps on glass substrates requires the development of phosphors that may be deposited at temperatures of 700 °C or lower. Several approaches are described here. A vacancy mechanism is shown to control the enhancement of crystallization in ZnGa 2O 4 by the introduction of CdO to form compounds of Zn 1− x Cd x Ga 2O 4:Mn. Here, sputtering targets and as-deposited thin films contain Cd atoms, but the annealed thin films undergo complete loss of Cd as they crystallize. It is also shown that a flux such as LiF maybe added to Zn 2SiO 4:Mn to lower crystallization temperature. Here it is likely that point defects Li Zn and F o permit charge compensation while lowering the crystallization temperature. High breakdown strength, high dielectric constant and transparent dielectric layers have been developed to permit long life OPEL on Corning 1737 glass substrates. Whereas it is commonly reported that SrTiO 3 and other perovskite titanate and zirconate dielectrics are not self-healing, it has been shown that a SrTiO 3 dielectric of thickness 2 μm prepared using three sub-layers does achieve self-healing. In conjunction with a Zn 2Si 0.5Ge 0.5O 4:Mn phosphor, excellent steep-threshold electroluminescence (EL) behaviour is observed with L50, the brightness 50 V over threshold at 60 Hz of over 300 cd/m 2. Finally, results for a new phosphor system Ga 2− x In x O 3:Eu on glass substrates are reported, in which the electric field for EL is reduced.

Luminescence properties of RP 1− xV xO 4: A (R=Y, Gd, La; A=Sm 3+, Er 3+x=0, 0.5, 1) thin films prepared by Pechini sol–gel process

Thin film phosphors with compositions of RP 1− x V x O 4: A (R=Y, Gd, La; A=Sm 3+, Er 3+; x=0, 0.5, 1) have been prepared by a Pechini sol–gel process. X-Ray diffraction, atomic force microscopy (AFM), photoluminescence excitation and emission spectra were utilized to characterize the thin film phosphors. The results of XRD showed that a solid solution formed in YV x P 1− x O 4: A film series from x=0 to x=1 with zircon structure, which also held for GdVO 4: A film. However, LaVO 4: A film crystallized with a different structure, monazite. AFM study revealed that the phosphor films consisted of homogeneous particles ranging from 90 to 400 nm depending on the compositions. Upon short ultraviolet excitation, the films exhibit the characteristic Sm 3+ 4G 5/2– 6H J ( J=5/2, 7/2, 9/2) emission in the red region and Er 3+ 2H 11/2, 4S 3/2– 4I 15/2 emission in the green region, respectively. With the increase of x values in YV x P 1− x O 4: Sm 3+ (Er 3+) films, the emission intensity of Sm 3+ (Er 3+) increases due to the increase of energy transfer probability from VO 4 3− to Sm 3+ (Er 3+). Due to the structural effects, the Sm 3+ (Er 3+) shows similar spectral properties in YVO 4 and GdVO 4 films, which are much different from those in LaVO 4 film.

Improved Cathodoluminescence Output Coupling of ZnS:Tb Thin-Film Phosphors Deposited on 2D SiO2 Corrugated Glass Substrate

A simple fabrication method of 2D corrugated layers and their suitability to enhance output coupling efficiency of a ZnS:Tb thin-film phosphor layer in an anode part of field emission display (FED) devices is discussed. For patterning of 2D dotted arrays of films, we used two-step irradiated hologram lithography and reactive ion etching. The formation of a wavelength-scale uniform 2D dotted array was confirmed by morphological analysis. We presented the finite-difference time-domain analysis for calculating the output light resulting from the insertion of a 2D corrugated layer into the interface between the glass substrate and the ZnS:Tb thin-film phosphor. A significant enhancement (a factor of 4.0-4.7) of the output coupling cathodoluminescence (CL) efficiency is reported in the low-voltage (0.5-4.5 kV) characteristics under electron-beam excitation for the ZnS:Tb thin-film phosphor deposited on a 2D corrugated substrate. The computational analysis, CL characterizations, and far-field measurement demonstrated that the 2D corrugated substrate served as diffraction scattering layers, increasing the output coupling efficiency, which is critically important for development of commercial FEDs employing thin-film phosphors. © 2003 The Electrochemical Society. All rights reserved.

Photoluminescence behavior of ZnGa 2O 4− xSe x:Mn 2+ thin film phosphors

Mn-doped ZnGa 2O 4− x Se x thin film phosphors have been grown using pulsed-laser ablation at the various growth conditions. Structural characterization was carried out on a series of ZnGa 2O 4− x Se x :Mn 2+ films grown on MgO(1 0 0) substrates using Zn-rich ceramic targets at various substrate temperatures and oxygen pressures. The films grown under different conditions not only have different crystallinity and surface morphology but also different Zn/Ga composition ratio. The luminescent results indicated that MgO (1 0 0) is one of the most promised substrates for the growth of high quality ZnGa 2O 4− x Se x :Mn 2+ films and the luminescent brightness is sensitive to the substrate temperature and oxygen pressure. In particular, the incorporation of Se into ZnGa 2O 4:Mn 2+ lattice induced a remarkable increase of photoluminescence (PL). The highest green emission intensity was observed with ZnGa 2O 3.925Se 0.075:Mn 2+ films, whose brightness was increased by a factor of 3.1 in comparison with that of ZnGa 2O 4:Mn 2+ films. This phosphor is promising for applications in flat panel displays.

Porous Phosphor Thin Films of Oxyfluoride SiO2–BaMgF4: Eu2+ Glass–Ceramics Prepared by Sol–Gel Method

Abstract Eu2+ ions were incorporated into SiO2–BaMgF4 glass–ceramic thin films using a sol–gel method. The addition of N,N-dimethylformamide to a starting solution resulted in a porous microstructure of the film prepared. The films exhibited blue emission peaking at 420 nm by excitation at 290 nm. The emission was effectively enhanced in the porous film owing to scattering absorption of the excitation light.

High-luminance thin-film electroluminescent devices using Y 2O 3:Mn phosphor

Mn-activated yttria (Y 2O 3:Mn) phosphor thin films, consisting of monoclinic Y 2O 3 host material, were prepared by r.f. magnetron sputtering. High-luminance yellow photoluminescence and electroluminescence emissions were obtained using Y 2O 3:Mn thin films prepared with a Mn content of 2 at.% at a substrate temperature of approximately 350 °C and postannealed at approximately 1020 °C in an Ar atmosphere. The obtainable electroluminescent (EL) characteristics of Y 2O 3:Mn thin-film EL (TFEL) devices were mainly related to the crystallinity of the thin-film emitting layers used in the devices. The obtained maximum luminance and luminous efficiency increased as the crystallinity of the monoclinic Y 2O 3:Mn thin-film emitting layers was improved. A luminance of 5110 cd/m 2 was obtained in a 1 kHz-driven TFEL device fabricated with monoclinic Y 2O 3:Mn phosphor thin film prepared under the optimized conditions.

Infrared emission from zinc sulfide: Rare-earth doped thin films

Infrared (IR) electroluminescent (EL) thin film phosphors were radio frequency magnetron sputter deposited by cosputtering of an undoped ZnS target together with ZnS: 1.5 mole % ErF3 or ZnS: 1.5 mole % NdF3 targets. The ZnS:ErF3 and ZnS:NdF3 thin film phosphors were annealed in a N2 ambient at temperatures ranging from 350 to 475 °C for 1 h to increase radiance. The maximum EL radiance observed was 28 μW/cm2 at 1550 nm for ZnS:ErF3, and 26 μW/cm2 at 910 nm and 15 μW/cm2 at 1060 nm for ZnS:NdF3 (at 40 V above the threshold voltage) after a 425 °C, 1 h anneal in nitrogen. For anneals above 425 °C visible emission increased, while near infrared (NIR) emission from both ZnS:ErF3 and ZnS:NdF3 was either constant or decreased. For ZnS:ErF3, the 1550 nm NIR peak decreased, but the 990 nm peak remained constant in intensity. The crystallinity of ZnS was improved by annealing, and these results are consistent with the postulate that residual defects limit the acceleration of “hot” electrons for anneals at ⩽425 °C. Under these conditions, hot electrons only have sufficient energy to excite Er+3 into the lower lying I413/2 excited state which leads to 1550 nm NIR emission. With increasing annealing temperatures, hot electrons can excite from the I415/2 ground state into higher energy excited states (e.g., the F47/2 state for 990 nm emission). The NIR emissions from ZnS:NdF3 at 910 and 1060 nm originate from the same excited state and both peaks exhibited maximum NIR intensities after annealing at 425 °C. While the emission spectra from Er were independent of annealing temperature, peak shifts were observed for Nd. These shifts were discussed in terms of the nephelauxetic effect and hybridization of the 5d–4f orbitals.

Enhanced green emission in ZnGa2O4:Mn thin film phosphors by Se doping

Mn-doped ZnGa2O4−xSex thin film phosphors have been grown using pulsed-laser ablation under various growth conditions. The structural characterization was carried out on a series of ZnGa2O4−xSex:Mn2+ films grown on MgO(100) substrates using Zn-rich ceramic targets. Zn-rich ceramic targets have been prepared to compensate the vaporization loss of Zn. The oxygen pressure was fixed at 100 mTorr and substrate temperatures were varied from 500 to 700 °C. The luminescence results indicated that MgO (100) is one of the most promised substrates for the growth of high-quality ZnGa2O4−xSex:Mn2+ films. In particular, the incorporation of Se into the ZnGa2O4 lattice induced a remarkable increase of photoluminescence. The highest green emission intensity was observed with ZnGa2O3.925Se0.075:Mn2+ films whose brightness was increased by a factor of 3.1 in comparison with that of ZnGa2O4:Mn2+ films. This phosphor may promise for application to the flat panel displays.

Ga-doping effects on electrical and luminescent properties of ZnO:(La,Eu)OF red phosphor thin films

Red thin-film phosphors were fabricated based on a ZnO:(La,Eu)OF nanocomposite structure where (La,Eu)OF nanoparticles were dispersed in a ZnO film matrix. The films were deposited on glass substrates by a sol-gel method at a low temperature of 600 °C using trifluoroacetic acid as a fluorine source. Doping gallium into the films suppressed the grain growth of ZnO, increased the optical band gap, and decreased electrical resistivity, which indicates that Ga3+ was selectively incorporated into the ZnO lattice. Eu3+ was practically doped in the LaOF lattice. As a result, strong red emissions due to the D05→F27 transition of Eu3+ were observed in both photo- (PL) and cathodoluminescence (CL) measurements. The efficiency of ultraviolet light excitation at 274 nm was promoted by the charge transfer from O2− to Eu3+ in PL. Ga doping was found to increase the CL intensity of the film, which was attributed to suppression of charge accumulation on the films.

Strong photoluminescence and cathodoluminescence due to f–f transitions in Eu3+ doped Al2O3 powders prepared by direct combustion synthesis and thin films deposited by laser ablation

In this letter, we report on fabrication and luminescent properties of phosphor powders and thin films of Eu3+ doped alumina Al2O3. The powders were fabricated by combustion synthesis process at a low temperature, 280 °C and showed strong photoluminescent and cathodoluminescent emissions. Powders of Eu3+ doped Al2O3 of concentration 1.0 mol % were deposited on quartz-glass substrates to form thin films by means of laser ablation. Under ultraviolet excitation and electron beam excitation, these samples containing microcrystalline structures showed strong luminescence due to f–f transitions, and the dominant transition was the hypersensitive D40→F72 red emission of Eu3+.