Phosphor Thin Films Research Articles

Characterization of sol‐gel SiO2:Ce,Tb powder and pulsed laser deposited thin film phosphors

AbstractThin films of SiO2:Ce,Tb (Ce = Tb = 0.5 mol%) nanoparticulate phosphor (nanophosphor) were ablated on Si (100) substrates using either the conventional pulsed laser deposition (PLD) or pulsed reactive crossed beam laser ablation (PRCLA) technique. Morphology and surface topography of the films were analysed with scanning electron microscopy (SEM) and atomic force microscopy (AFM) respectively. The chemical composition and thicknesses of the films were determined by Rutherford backscattering spectroscopy (RBS). Luminescence properties of the films were studied with cathodoluminescence (CL) spectroscopy and a 325 nm HeCd laser. Enhanced green cathodoluminescence and photoluminescence (PL) associated with 5D4→7F4 transitions in Tb3+ was observed at ∼540 nm in powder and thin film samples, and is attributed to non‐radiative energy transfer from co‐doped Ce3+. Luminescence intensities of the films and that of the SiO2:Ce,Tb powder used to make the films are compared. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication of Carbon Nanofiber Emitters for Excitation of Organic Phosphor Thin Films

For applications to a novel low-voltage acceleration field emission display, carbon nanofiber (CNF) emitters were fabricated using a screen printing method. The two types of CNF of different lengths, normal-length CNFs, and cut CNFs were examined. A current density of 1.4 mA/cm2 was achieved at 10 V/µm in CNF emitters prepared from the paste composed of normal-length CNFs (1 wt %), glass paste (6 wt %), and gold nanometal ink (30 wt %). The field enhancement factor β in the Fowler–Nordheim equation was ca. 5800. CNF emitters without gold nanometal ink showed low performance. Emitter performance was determined on the basis of the results of scanning electron microscopy (SEM) and field emission characteristics.

アパタイト構造La9.33(Si6O24-xNx)O2:Tb3+酸窒化物蛍光体薄膜の作製

アパタイト構造La9.33(Si6O24-xNx)O2:Tb3+酸窒化物蛍光体薄膜の作製

Pechinin synthesis and luminescence properties of Y 3Ga 5O 12(YGG):Tb thin film

YGG:Tb thin films were successfully prepared by Pechni sol–gel process. The structure, surface morphology, evolution of film crystallization and their luminescent properties were investigated. We find the annealing process is very important to the YGG:Tb film crystallization. Uniform crack-free films can be obtained by conventional annealing for 1 h after rapid thermal treating for 10 min at 800 °C. The excitation and emission spectra of photoluminescence (PL) were used to characterize the luminescent properties. The excitation spectrum of YGG:Tb is dominated by the 4f–4f5d transition of Tb 3+at 260 nm. The emission peaks of phosphor thin film lie at 488 and 543 nm. It can be used as a promising phosphor material for FED or ELD application.

Strong perturbation of the guided light within Y2O3:Eu3+ thin-film phosphors coated with two-dimensional air-hole photonic crystal arrays

Two-dimensional (2D) triangular-lattice air-hole nanoarrays of either SiO2 or SiNx were fabricated with nanosphere lithography as photonic crystal layers (PCLs) on sol-gel derived Y2O3:Eu3+ thin-film phosphors (TFPs). The effects of varying the air fill factor of the 2D PCLs on the light extraction efficiency of the TFPs were investigated. The integrated and normally directed photoluminescence extraction efficiencies were found to be improved by coating with 2D SiNx PCLs by factors of above 5.9 and 9.4, respectively; the 2D SiNx PCLs perturb the guided light more effectively than the 2D SiO2 PCLs because of their larger refractive index contrast.

SURFACE MORPHOLOGY AND PHOTOLUMINESCENCE CHARACTERISTICS OF Sm-DOPED YVO4 THIN FILMS

Surface morphology and crystallinity of YVO 4: Sm 3+ thin films have an influence on the photoluminescence characteristics. The YVO 4: Sm 3+ films have been deposited on Al 2 O 3 (0001) substrates using pulsed laser deposition method. The films were grown at the various substrate temperatures changing from 500 to 700°C. The crystallinity and surface morphology of the films were investigated using X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. The results of XRD showed that YVO 4: Sm 3+ films had a 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 and the emitted radiation was dominated by the red emission peak at 620 nm radiated from the transition of 5 D 0-7 F 2. The crystallinity, surface morphology, and photoluminescence spectra of thin-film phosphors were highly dependent on the substrate temperature. The surface roughness and photoluminescence intensity of the films showed similar behavior as a function of substrate temperature.

Full‐Color Mesophase Silicate Thin Film Phosphors Incorporated with Rare Earth Ions and Photosensitizers

Full-color mesophase silicate thin film phosphors incorporated with rare earth ions and photosensitizers exhibit multicolor photoluminescence that covere the whole visible range under UV excitation. The multiple colors can be finely tuned by varying the relative concentrations of the RE trivalent ions and photosensitizers. The mesophase silica thin films have promising applications in display field.

Effect of Substrate Temperature on the Structural and Luminescent Characteristics of RF-Magnetron-Sputtered ZnGa2O4 : Dy3 + Thin Films

phosphor thin films were deposited on quartz substrates by radio frequency (rf) magnetron sputtering and the effect of substrate temperature on its structural and luminescent properties was investigated. Polycrystalline film could be deposited even at room temperature. The crystalline behavior, ratio, and surface morphology of the films were found to be highly sensitive to substrate temperature. Under UV illumination, the as-deposited films at and above gave white luminescence even without any postdeposition treatments. The photoluminescent (PL) emission can be attributed to the combined effect of multicolor emissions from the single luminescence center via host-sensitization. Maximum PL emission intensity was observed for the film deposited at , and the CIE chromaticity coordinates of the emission were determined to be .

Study on X-ray Absorption Near Edge Structure of Eu Centers in CaAl2O4:Eu Phosphor Thin Films Prepared by Pulsed Laser Deposition

X-ray absorption fine structure and photoluminescence studies of CaAl2O4:Eu phosphor thin films prepared by pulse laser deposition have been carried out. The ratio of the Eu2+/Eu3+ content is estimated from the Eu-LIII edge X-ray absorption near-edge structure spectra. It has been found that Eu2+ predominates in the as-deposited films. The ratio of Eu2+ is further increased to 95% by post-annealing only for the films deposited under an almost stoichiometric condition in the laser-induced plasma, which is crystallized as CaAl2O4 and emits blue light due to Eu2+ in CaAl2O4 crystal. For the film deposited under a non-stoichiometric condition, The Eu3+ ratio is increased by post-annealing even in a reducing atmosphere, resulting in poor luminescence intensity and a color shift of Eu2+.

Structural and Luminescent Properties of Eu-Doped GdVO4 Thin-Film Phosphors Grown on Various Substrates by Using Pulsed Laser Deposition

Structural and Luminescent Properties of Eu-Doped GdVO4 Thin-Film Phosphors Grown on Various Substrates by Using Pulsed Laser Deposition

Efficiency enhancement by aluminum addition to CaTiO3:Pr3+ phosphor thin films

The mechanism of enhancement of the red emission efficiency from CaTiO3:Pr3+ thin film by Al addition has been investigated. Al-ions have been attracting interest as a sensitizer to improve the luminescent efficiency of phosphors. Also, influence of Al-doping on the crystallization, surface morphology and luminescent properties of CaTiO3:Pr3+ thin films have been discussed. CaTiO3:Pr3+ and Al-doped CaTiO3:Pr3+ films were grown using pulsed laser deposition technique on Al2O3 (0001) substrates under different substrate temperatures and oxygen pressures. The crystalline phase and surface morphology of the films were very dependent on the oxygen pressure and substrate temperature and they affected the luminescent brightness of the films. The crystalline structure and microstructure of these films have been characterized by X-ray diffraction and electron microscopy and their luminescent properties have been evaluated at room temperature using a luminescence spectrometer and excitation by a broadband incoherent ultraviolet light source with a dominant excitation wavelength of 325 nm. In particular, the incorporation of Al3+ ions into CaTiO3 lattice could induce a remarkable increase of photoluminescence. The enhancement of luminescence for Al-doped films may result not only from the improved crystallinity but also from the reduced internal reflections caused by rougher surfaces. Also, the luminescent intensity and surface roughness of the films exhibited similar behavior as a function of oxygen pressure.

Enhanced extraction efficiency of Y2O3:Eu3+ thin-film phosphors coated with hexagonally close-packed polystyrene nanosphere monolayers

A hexagonally close-packed, two-dimensional (2D) polystyrene (PS) nanosphere photonic crystal (PC) monolayer was built on a sol-gel derived Y2O3:Eu3+ thin film in an attempt to improve the efficiency of light extraction from the phosphor side of the Y2O3:Eu3+ thin film. The effects of crystallinity and particle size of the 2D PS nanosphere/air PC layer on the extraction efficiencies of the Y2O3:Eu3+ thin-film phosphors were investigated. The integrated photoluminescence extraction was improved by a factor of over 3.7 compared to that of a conventional Y2O3:Eu3+ thin film, by adding a 2D PS monolayer array of 580nm sized nanospheres with high crystallinity.

Sol–gel synthesis and luminescence property of ZnO:(La,Eu)Cl nanocomposite thin films

A kind of ZnO:(La, Eu)Cl nanocomposite thin film phosphor with strong red emission was synthesized by the sol–gel process. X-ray diffraction and scanning electron microscopy characterization indicate that the films were composed of nano-sized grains and a LaOCl phase appeared accompanying with (100) oriented ZnO phase after annealed at 600 °C in oxygen. The photoluminescence properties were investigated by measuring the excitation and emission spectra. These luminescence results suggested that Eu 3+ ions could incorporate into the LaOCl lattice and charge transfer occurred between LaOCl phase and Eu 3+ ions. La co-doping with Eu-Cl leads to the improvement of the red luminescence of Eu 3+ and also suppressed the broad green emission of ZnO host.

Structural effect of a two-dimensional SiO2 photonic crystal layer on extraction efficiency in sputter-deposited Y2O3:Eu3+ thin-film phosphors

We determined the effects of varying the structural parameters of two-dimensional (2D) square lattice SiO2 photonic crystal (PC) arrays on the efficiency of extraction of the photoluminescence (PL) of sputter-deposited Y2O3:Eu3+ thin films, in which the interface between the phosphor layer and the quartz substrate was modified with the 2D SiO2 PC pattern. The structural parameters of the 2D PC pattern were optimized according to their effects on the light extraction efficiency and similar trends were found for both the as-grown and the post-annealed samples; the samples with lattice constants in the range 400−600 nm exhibit the largest enhancement, there is increased enhancement with pattern height increases up to ∼420 nm, and the samples with a filling ratio of ∼0.20 exhibit the maximum enhancement of the extraction efficiency. For 2D PC patterns with a depth of 420 nm, a lattice constant of 600 nm, and a filling ratio of 0.2, the optimum PL extraction efficiencies of as-grown (350 °C) and post-annealed (900 °C) Y2O3:Eu3+ thin-film phosphors were improved by factors of more than 8.6 and 4.8, respectively, with respect to those of flat Y2O3:Eu3+ thin films. We investigated the reasons for this difference between the enhancements of the extraction efficiencies of the as-grown and post-annealed Y2O3:Eu3+ thin films deposited on 2D PC quartz substrates, in order to determine the factors affecting the extraction efficiencies of 2D PC layer assisted thin-film phosphors.

Cathodoluminescence degradation of Y2SiO5:Ce thin films

Cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y2SiO5:Ce) phosphor thin films grown by pulsed laser deposition were investigated for possible application in low voltage field emission displays (FEDs). A thin layer of tin oxide (SnO2) was ablated on some of the films in order to investigate the effect of the coated layer on the degradation of the CL intensity. 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 2keV energy electrons and with beam current densities of 26 and 52mAcm−2. Measurements were done in high vacuum and in oxygen pressures of 1×10−8, 1×10−7, and 1×10−6Torr. Residual gas mass analysis showed that the adventitious carbon (C) was removed from the surface as volatile gas species, which is consistent with the electron stimulated surface chemical reaction model. The SnO2 coated thin films resulted in a lower but more stable CL intensity than the uncoated thin films. The degradation of the CL intensity was much less for the thin films after the same time period than for the Y2SiO5:Ce powders.

Cathodoluminescent Properties of Sol-Gel Derived Gd<sub>2</sub>O<sub>3</sub>: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.

Structural and luminescence properties of pulsed laser deposited green-emitting Zn 2SiO 4:Mn phosphor thin films

The structural and photoluminescent (PL) properties of Zn 2(1− x ) Mn x SiO 4 (1 ⩽ x ⩽ 5) thin film phosphors grown using a pulsed laser deposition technique have been investigated. The effect of systematic variation of oxygen partial pressures (O 2 pp) (100, 300, 500 and 700 mTorr) during the growth of these thin films has been studied. Thin film grown on silicon substrate at 750 °C and in situ annealed in 300 mTorr of O 2 pp exhibits superior PL property; ex situ annealing at higher temperatures improves the PL intensity.

Improved photoluminescence of pulsed-laser-ablated Y1-xGdxVO4:Eu3+ thin film phosphors by Gd substitution

Gd-substituted Y1-xGdxVO4:Eu3+ luminescent thin films have been grown on Al2O3(0001) substrates using pulsed-laser deposition. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The crystallinity, surface morphology, and photoluminescence (PL) of the films are highly dependent on the amount of Gd. The photoluminescence (PL) brightness data obtained from Y1-xGdxVO4:Eu3+ films grown under optimized conditions have indicated that the PL brightness is more dependent on the surface roughness than the crystallinity of the films. In particular, the incorporation of Gd into the YVO4 lattice could induce a remarkable increase of PL. The highest emission intensity was observed with Y0.57Gd0.40Eu0.03VO4 thin film whose brightness was increased by a factor of 2.5 and 1.9 in comparison with that of YVO4:Eu3+ and GdVO4:Eu3+ films, respectively. This phosphor have application to flat panel displays.

Effects of SnO 2 surface coating on the degradation of ZnS thin film phosphor

Pulsed laser deposited ZnS bare and SnO 2 coated ultra thin films were subjected to prolonged electron beam bombardment with 2 keV energy and a steady 44 mA/cm 2 current density, in 1 × 10 −6 Torr O 2 pressure backfilled from a base pressure of 3 × 10 −9 Torr at room temperature. Auger electron spectroscopy (AES) was used to monitor changes of the surface chemical composition of both the bare and coated phosphor films during electron bombardment. Degradation was manifested by the decrease of sulphur and accumulation of oxygen on the surface of the bare phosphor. However, with the SnO 2 coating this phenomenon was delayed until the protective SnO 2 was depleted on the surface through dissociation and reduction.

The microstructure and cathodoluminescence characteristics of sputtered Zn 2SiO 4:Ti phosphor thin films

The structural characteristics and cathodoluminescent properties of Ti doped Zn 2SiO 4 films deposited by radio-frequency sputtering are studied. The as-deposited Zn 2SiO 4:Ti film is amorphous and it transforms to α-Zn 2SiO 4 phase after annealing at 900 °C or higher temperature. For the 1000 °C-annealed film, transmission electron microscopy reveals homogeneous α-Zn 2SiO 4 crystals with grain size about 330 nm. Also, the absorption edge at 225 nm corresponds well to the band gap of α-Zn 2SiO 4. According to the cathodoluminescent measurement, blue-light emission (at 403 nm) is observed only when the Zn 2SiO 4:Ti film becomes crystallized after high-temperature annealing. The emission intensity of Zn 2SiO 4:Ti films increases with increasing Ti concentration, and it can be significantly intensified to 100 times by doping 1 mol% of Ti into the Zn 2SiO 4 films.