Phosphor Thin Films Research Articles

Improved cathodoluminescent characteristics of Y2O3:Eu3+ thin films by Li-doping

Y2O3:Eu3+ luminescent thin films have been studied as a potential red phosphor thin film for application in field emission display. Y2O3:Eu3+ and Li-doped Y2O3:Eu3+ films have been grown on Al2O3(0001) substrates using a pulsed laser deposition technique at substrate temperature of 600 °C under the various oxygen pressures. The cathodoluminescent intensity of the Y2O3:Eu3+ films were highly dependent not only on the crystallinity, but also on the surface roughness of the films. Cathodoluminescent spectra for both Y2O3:Eu3+ and Li-doped Y2O3:Eu3+ films were dominated by the red emission peak at 612 nm radiated by the transition of 5D0-7F2 within europium and the brightness of the Li-doped films was increased by a factor of 1.4 in comparison with that of the Y2O3:Eu3+ films. It is understood that Li ions affect the luminescence of the Y2O3:Eu3+ films by influencing its crystallinity and surface roughness. The cathodoluminescent intensity and surface roughness had similar behavior as a function of oxygen pressure.

Zinc Gallate (ZnGa2O4)박막 형광체의 합성과 발광특성

Zinc gallate (ZnGa₂O₄) thin film phosphors have been formed on ITO glass substrates by a sol-gel spinning coating method. For the formation of the film phosphors, the starting materials of zinc acetate dihydrate, gallium nitrate hydrate and 2-methoxyethanol as a solution were used. The thin films deposited were firstly dried at 100℃ and fired at 500℃ or 600℃ for 30 min and then, annealed at 500℃ or 600℃ for 30 min under an annealing atmosphere of 3% H₂/Ar. The thin films deposited on ITO glass plates showed the (220), (222), (400), (422), (511), and (440) peaks of spinel structure as well as the (311) peak indicating a standard powder diffraction pattern. The surface morphologies of the thin film phosphors were observed with a firing and an annealing condition. The ZnGa₂O₄ film phosphors showed the blue emission spectra around 410 ㎚ as well as the emission spectra in the UV region (360-380 ㎚).

Correlation between structural changes and luminescent properties of ZnMgS:Mn thin film phosphor with annealing temperature

With varying rapid thermal annealing temperature, luminescent properties of Zn 0.75 Mg 0.25 S :Mn thin film deposited by RF-magnetron sputtering technique were investigated. Although all samples were deposited from identical source composition, it was found that a main peak wavelength of photoluminescence of Zn 0.75 Mg 0.25 S :Mn depended on RTA temperatures and it shifted toward shorter wavelength upon the increase of RTA temperature. The same dependence of wavelength on RTA temperature was also observed in cathodoluminescence as well as electroluminescence measurements. It is noticeable that Zn 0.75 Mg 0.25 S :Mn thin film phosphor in this study showed more reddish emission than those of the previous studies. It was revealed that changes of the luminescent properties were originated from structural changes in Zn 0.75 Mg 0.25 S :Mn thin film phosphor from cubic to hexagonal phases using X-ray pole figure mapping, and the growing up of hexagonal phase mainly caused cracks and porous morphology on the surface of thin films. It is suggested that the phase transition would be the origin of luminescent property changes with respect to rapid thermal annealing temperature.

Optical Properties of ZnCdS:I Orange and ZnSTe:I White Thin Film Phosphor for High Ra White LED

In order to develop visible thin film phosphors, we have for the first time prepared ZnCdS and ZnSTe doped with Iodine (I) using low-pressure MOCVD method. ZnCdS:I, of which Cd composition was calibrated to match the lattice constant to that of substrate and the band gap to absorption peak, showed a orange broad emission consist of yellow near band edge emission and red SA emission. Isoelectronic Te in ZnS indicates strong blue-green emissions, whilst I donor impurity in ZnS shows strong red SA emissions. A typical ZnSTe:I thin film shows two broad emission bands locating at around 500 and 680 nm, respectively, indicating Ra∼90. It was shown that high Ra thin film phosphor can be realized by single material (ZnSTe:I), and that MOCVD method is capable for controlling the thickness and doping profile to obtain uniform white emission pattern.

Pulsed Laser Deposition Growth of CaMgSi[sub 2]O[sub 6]:Eu[sup 2+] Thin Film Phosphors

CaMgSi 2 O 6 :Eu 2+ (CMS) phosphors, which are comparable to BaMgAl 10 O 17 :Eu 2+ phosphors, were prepared in the form of thin films deposited on quartz glass using a pulsed laser deposition technique. The luminescent and structural properties of the CMS thin film phosphors were monitored as a function of key processing parameters such as, the partial pressure of oxygen inside the deposition chamber, laser energy density, and the type of post-deposition treatments used. By optimizing these processing parameters, CMS thin films with large homogenous areas and a high photoluminescence could be produced.

PLD(Pulsed Laser Deposition)를 이용한 청색 박막 형광체의 제조 및 특성분석

It is well known that BaMgAl₁?O₁?:Eu²? (BAM) and CaMgSi₂O?:Eu²? (CMS) are a highly efficient blue phosphor. However, these phosphors in the form of thin films have not yet been realized due to technical difficulties. We prepared thin film type BAM and CMS phosphors on quartz glass substrate using a pulsed laser deposition technique. The luminescent and structural properties of thin film phosphors were monitored as a function of key processing parameters such as oxygen partial pressure inside the deposition chamber, deposition time, laser energy density and the type of post-deposition treatments used. Even though we could not obtain single homogenous phases, thin films with large homogenous areas and a high photoluminescence could be produced by optimizing these processing parameters.

ZnGa2O4 thin films fabricated by Sol-gel spinning coating process

ZnGa2O4 thin film phosphors have been synthesized on ITO coated glass and soda-lime glass at a firing temperature of 500∘C and an annealing temperature of 500∘C and 600∘C via a chemical solution method using Zinc acetate dihydrate, Gallium nitrate hydrate and 2-methoxiethanol as a solution. XRD patterns of the film phosphors synthesized showed the peaks of ZnGa2O4 crystalline phases. AFM surface morphologies of the ZnGa2O4 thin film phosphors revealed marked differences according to an annealing temperature of 500∘C and 600∘C under an annealing atmosphere (3% H2/Ar). On the other hand, the sheet resistance of ZnGa2O4 thin film phosphors, which were measured by four-point probe instrument, was approximately 5.76 Ω /square and 7.86 Ω /square with annealing temperature, respectively. The ZnGa2O4 thin film phosphors exhibited blue emission spectra with peak wavelength of 434 nm and 436 nm by ultra-violet excitation around 230 nm.

Blue-Light Emission from Undoped and Rare Earth-Doped Wide Bandgap Oxides

Rare earth-doped oxide thin-film phosphors may emerge as an alternate choice for the blue phosphor, due to their chemical and thermal stability in high vacuum and absence of corrosive gas emission under electron bombardment. The blue phosphors in this study were activated in air at temperatures suitable for glass substrates, which have been used in a number of applications. The effects of rare earth ions and oxide hosts on the blue-light-emitting properties of phosphors are discussed. In addition, novel blue-light emission was observed in certain typical undoped wide bandgap oxides. The luminescence of the oxides depends on the growth and annealing conditions under different atmospheres, suggesting that it is associated with the presence of oxygen vacancies. Radiative processes related to oxygen vacancies were also presented.

Characterization of AlN:Mn thin film phosphors prepared by metalorganic chemical vapor deposition

The structural and luminescent properties of AlN:Mn films, which showed red-orange luminescence originated from the transition of 3d-electrons in a Mn ion, were investigated. The samples were grown on sapphire (0 0 0 1) wafers by an atmospheric-pressure metalorganic chemical vapor deposition at 1050 °C. The grown films were polycrystal oriented preferentially towards the 〈 0 0 0 1 〉 direction of wurtzite structure. It is suggested from the dependence of Mn concentration ( C Mn ) on the lattice constant and the low-temperature photoluminescence spectrum that most of the Mn atoms occupy the lattice sites for C Mn up to about 1 × 10 20 cm - 3 . The samples exhibited bright cathodoluminescence reflecting the improved crystalline quality compared to that of the low-temperature-grown samples. The highest luminance, 245 cd/m 2, has been obtained from the layer with C Mn of 3 × 10 19 cm - 3 under the excitation conditions of 5 kV and 0.1 mA/cm 2 as an accelerating voltage and a current density, respectively.

Cathode luminescence characteristics of ZnGa 2O 4 phosphor thin films with the doped activator

The zincgallate (ZnGa 2O 4) phosphor thin film was grown using RF magnetron sputtering system at various process parameters. A ZnGa 2O 4 phosphor thin film was deposited on Si(1 0 0) substrate and annealed by a rapid thermal processor (RTP). The X-ray diffractometer (XRD) patterns indicate that the Mn-doped ZnGa 2O 4 phosphor thin film shows a (3 1 1) main peak and a spinel phase. A ZnGa 2O 4 phosphor thin film has better crystallization due to increased substrate, annealing temperature and deposition time. Also the ZnGa 2O 4:Mn phosphor thin film shows green emission (510 nm, 4T 1→ 6A 1), and the ZnGa 2O 4:Cr phosphor thin film shows red emission (705 nm, 4A 2→ 4T 2).

Analysis of the factors governing the enhanced photoluminescence brightness of Li-doped Y2O3:Eu thin-film phosphors

The authors studied the Li concentration dependence of the internal efficiency and extraction efficiency contributions to the enhanced photoluminescence (PL) brightness of the Li-doped Y2O3:Eu thin films. Experiments conducted with excitation at a wavelength of 254nm showed that adding 20mol% Li2CO3 to conventional Y2O3:Eu thin films improved their PL brightness by a factor of over 7.0. This improvement is attributed to enhanced internal factors (crystallinity, grains, and substitution of interstitial oxygen) and the increased optical volume (thickness), as well as the reduction of photon trapping in the high-index guiding layers of the Y2O3:Eu thin films. They also discuss how to quantitatively determine the contributions of the internal efficiency, the extraction efficiency, and the optical volume to the enhanced PL brightness of the Li-doped Y2O3:Eu thin-film phosphors.

Characterization of Y2SiO5:Ce thin films

Uncoated and SnO2-coated Y2SiO5:Ce thin film phosphors grown on Si (100) substrates by a pulsed laser deposition technique were characterized with scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-Ray analysis (EDS) and X-Ray diffraction (XRD). Cathodoluminescence (CL) of both the uncoated and SnO2-coated thin film phosphors was investigated for possible application in low voltage field emission displays (FEDs). Blue emission with peak values at 440 and 500nm was from spherically shaped particles distributed unevenly on the surfaces of both the uncoated and coated thin film phosphors.

Photoluminescence characteristics of ZnGa2O4 thin films prepared by chemical solution method

Zinc gallate (ZnGa2O4) thin film phosphors have been formed on ITO glass substrates by a chemical solution method with starting materials of zinc acetate dihydrate, gallium nitrate hydrate and 2-methoxiethanol as a solution. The thin films were firstly dried at 100 °C and fired at 500 °C for 30 min and then, annealed at 500 °C and 600 °C for 30 min under an annealing atmosphere of 3% H2/Ar. XRD patterns of the thin film phosphors showed (311) and (220) peak indicating ZnGa2O4 crystalline phase in which all the (311) peaks of the film phosphors synthesized on ITO glass and soda-lime glass revealed high intensity with increasing annealing temperature from 500 °C to 600 °C. The ZnGa2O4 thin film phosphors represented marked change in AFM surface morphologies according to an annealing temperature under an annealing atmosphere (3% H2/Ar). The film phosphor, annealed at 600 °C, showed the embossed pattern with relatively regular spacing in AFM surface morphology. The ZnGa2O4 thin film phosphors formed on ITO glass, which were annealed at different temperatures and showed distinctive spectra with peak wavelengths of 434 nm and 436 nm in the blue emission region.

Photoluminescence Behavior of Ti-Doped Zn2SiO4 Thin Film Phosphors

This work investigates the luminescent properties and structure of Zn2SiO4:Ti thin-film phosphor, before and after annealing up to 1000oC. The Zn2SiO4:Ti films are fabricated by RF sputtering using ceramic target. After annealing at 800oC the beta-Zn2SiO4 phase is formed, but this phase is not suitable for the application in electroluminescence. The willemite structure (alpha-Zn2SiO4) is formed after annealing at 900oC or higher temperature. Concurrently, the Zn-O-Si bonding is observed by XPS analysis and it corresponds to the willemite structure. A broad PL peak locates at 386 nm is observed for the 700oC annealed Zn2SiO4:Ti film. However, three PL peaks, centered at 380 nm, 398 nm and 402 nm, can be observed in the 900oC annealed sample. All films exhibit a high transmission (>80%) in the visible spectrum, either before or after annealing.

Photoluminescence of ZnO:Er Thin Film Phosphors Deposited by RF Magnetron Sputtering

Photoluminescence of ZnO:Er Thin Film Phosphors Deposited by RF Magnetron Sputtering

Production and shaping of high performance phosphors by using the sol–gel process: Yttrium aluminum garnet (Y3Al5O12)

Luminescent Y3Al5O12:Tb3+ (YAG:Tb3+) phosphor thin films and powders have been successfully prepared by the sol–gel route from alkoxide precursors. Advanced coatings were produced by spray and dip-coating from stabilized sols. X-ray diffraction (XRD), attenuated total reflectance/Fourier transform infrared spectroscopy (ATR/FTIR) and atomic force microscopy (AFM) were used to investigate the structure and morphology of layers. YAG phases of high purity were obtained for both powders and films. AFM study revealed coatings of homogeneous topography, whatever the deposition technique. However, dip-coated samples exhibited a much smoother topography, characterized by a root mean square (rms) roughness much lower than that of spray-coated ones. Laser induced emission spectra and decay times of Tb3+ ions in a spray-coated film were recorded. Measurements exhibit the characteristic green emission of Tb3+. Effectiveness of the Tb3+ doped coatings under UV excitation is also illustrated by pictures.

Pulsed laser deposition of Gd 3O 4Br:Tb 3+ films and their emission properties

Gd 3O 4Br:Tb thin film phosphors are fabricated by pulsed laser deposition on Si (1 1 1) substrate at room temperature and their photoluminescence (PL) properties have been studied. When the films are excited by UV light, several characteristic emissions of Tb 3+ are detected. When the emission of Tb 3+ are monitored, a broad excitation band centered at 265 nm and two excitation lines peaked at 276 and 313 nm are found, which can be assigned to 7F 6(4f 8)→5d of Tb 3+ excitation and to 8S 7/ 2 → 6 I J and 8S 7/ 2 → 6P J of Gd 3+ excitation, respectively. The oxygen pressure and post-annealing temperature are changed during the films growth, and it is proved that the film deposited with 20 Pa oxygen pressure and post-annealed at 1000°C shows prominent PL brightness.

Preparation and properties of thin ZnS:Cu films phosphors

Thin films of ZnS and ZnS:Cu were prepared by an original metalorganic chemical vapour deposition (MOCVD) method under atmospheric pressure onto a glass substrate heated up to 230–250 °C. The film thickness varied from 0.6 to 1 μm. The thin films were doped with Cu and Cl by the thermal treatment during 1 h at 600 °C at atmospheric pressure in the blend composed of a ZnS powder with Cu and Cl compounds. These films were used for fabrication of the thin film electroluminescent (TFEL) devices with a conventional double insulating structure. The structural properties were investigated by use of X-ray diffraction (XRD) techniques and atomic force microscopy (AFM). Electroluminescent (EL) spectra, electrical and EL characteristics were investigated. The EL spectra and characteristics as well as structural parameters depend on the growth conditions and significantly modified after the annealing. Blue color emission with brightness of 10 cd m − 2 under a sine wave excitation at 60 V and 5 kHz was obtained. The degradation behavior of the TFEL devices with ZnS:[Cu, Cl] films fabricated using an original non-vacuum methods of deposition and annealing is the same as that of commercial thin film phosphor.

P-226L: Late-News Poster: Development of Technique for High Resolution and Low Temperature Crystallization of SrGa[sub 2]S[sub 4] Thin Film Phosphors for FEDs

We have studied to prepare rare-earth-activated SrGa2S4 thin film phosphors with commercial level emission properties. The thin film phosphors with high resolution patters could be successfully prepared by an ion implantation. Moreover, it was also shown that the films could be crystallized even at low temperature of around 500 °C by a laser annealing. Therefore, these techniques are promising to realize FEDs with practical level.

Pulsed Laser Deposited Oxide Green Emitting Thin Film Phosphors : Optimization of Growth Conditions

AbstractStructural and photoluminescence (PL) properties of Zn2(1-x)MnxSiO4 (1 ≤ x ≤ 5) and diffuse reflectance spectroscopy (DRS) and morphological studies of ZnGa2O4:Mn thin film green emitting phosphors grown using pulsed laser deposition (PLD) technique have been investigated. Zn2(1-x)MnxSiO4 thin films grown on Si substrate at 700°C in 300 mTorr of oxygen partial pressure, upon ex-situ annealing at higher temperatures exhibit superior PL intensity. ZnGa2O4:Mn phosphor thin films grown on quartz substrate at 650oC and in-situ annealed in 300mTorr of oxygen partial pressure show better emission intensity. For both Zn2SiO4:Mn and ZnGa2O4:Mn phosphors, luminescence can be assigned to 4T1 – 6A1 transition of Mn2+ within the 3d orbital giving rise to emission at 525 and 503 nm, respectively.