The effect of different gas atmospheres on luminescent properties of pulsed laser ablated SrAl2O4:Eu,Dy thinfilms

SrAl₂O₄:Eu²⁺,Dy³⁺ thin films were grown on Si (1 0 0) substrates using the pulsed laser deposition (PLD) technique to investigate the effect of vacuum, oxygen (O₂) and argon (Ar) deposition atmospheres on the structural, morphological, photoluminescence (PL) and cathodoluminescence (CL) properties of the films. The films were ablated using a 248 nm KrF excimer laser. Atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and fluorescence spectrophotometry were used to characterize the thin films. Auger electron spectroscopy (AES) combined with CL spectroscopy were employed for the surface characterization and electron-beam induced degradation of the films. Better PL intensities were obtained from the unannealed films prepared in Ar and O₂ atmospheres with respect to those prepared in vacuum. A stable green emission peak at 515 nm, attributed to 4f⁶5d¹→4f⁷ Eu²⁺ transitions were obtained with less intense peaks at 619 nm, which were attributed to transitions in Eu³⁺. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The CL intensity increased under prolonged electron bombardment during the removal of C due to electron stimulated surface chemical reactions (ESSCRs) on the surface of the SrAl₂O₄:Eu²⁺, Dy³⁺ thin films. The CL stabilized and stayed constant thereafter.     

X-ray photoelectron spectroscopy analysis for undegraded and degraded Gd2O2S:Tb phosphor thin films

This paper presents the X-ray Photoelectron Spectroscopy (XPS) analysis for the undegraded and degraded Gd₂O₂S:Tb³⁺ thin film phosphor. The thin films were grown with the pulsed laser deposition (PLD) technique. XPS measurements were done on Gd₂O₂S:Tb³⁺ phosphor thin films before and after electron degradation. The XPS technique has proven the presence of Gd₂O₃ on the degraded and undegraded thin film spots. The presence of the SO₂ bonding was also detected after degradation. This clearly indicates that surface reactions did occur during prolonged electron bombardment in an oxygen atmosphere.     

XPS analysis and luminescence properties of thin films deposited by the pulsed laser deposition technique

This paper presents the effect of substrate temperature and oxygen partial pressure on the photoluminescence (PL) intensity of the Gd₂O₂S:Tb^3?+? thin films that were grown by using pulsed laser deposition (PLD). The PL intensity increased with an increase in the oxygen partial pressure and substrate temperature. The thin film deposited at an oxygen pressure of 900 mTorr and substrate temperature of 900°C was found to be the best in terms of the PL intensity of the Gd₂O₂S:Tb^3?+? emission. The main emission peak due to the ⁵D₄–⁷F₅ transition of Tb was measured at a wavelength of 545 nm. The stability of these thin films under prolonged electron bombardment was tested with a combination of techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and Cathodoluminescence (CL) spectroscopy. It was shown that the main reason for the degradation in luminescence intensity under electron bombardment is the formation of a non-luminescent Gd₂O₃ layer, with small amounts of Gd₂S₃, on the surface.     

Auger electron/X-ray photoelectron and cathodoluminescent spectroscopic studies of pulsed laser ablated SrAl2O4:Eu,Dy thin films

Auger electron/X-ray photoelectron and cathodoluminescent (CL) spectroscopic studies were conducted on pulsed laser deposited SrAl₂O₄:Eu²⁺,Dy³⁺ thin films and the correlation between the surface chemical reactions and the decrease in the CL intensity was determined. The Auger electron and the CL data were collected simultaneously in a vacuum chamber either maintained at base pressure or backfilled with oxygen gas. The data were collected when the films were irradiated for 14 h with 2 keV electrons. The CL emission peak attributed to the 4f⁶5d¹ → 4f⁷ transitions was observed at ∼521 nm and the CL intensity of the peaks degraded at different rates in different vacuum conditions. X-ray photoelectron spectroscopy (XPS) data collected from degraded films suggest that strontium oxide (SrO) and aliminium oxide (Al₂O₃) were formed on the surface of the film as a result of electron stimulated surface chemical reaction (ESSCR).     

PL and CL degradation and characteristics of SrAl2O4: Eu,Dy phosphors

Strontium aluminate phosphors are ideal for luminescent infrastructure materials. Their brightness and persistent glow time are much higher than previously used sulphide phosphors. Strontium aluminates prepared by the sol–gel and combustion methods are compared with commercially available strontium aluminate. High luminescent efficient SrAl₂O₄:Eu²⁺,Dy³⁺ pulsed laser deposited (PLD) thin films were also produced using the commercially available powder. Photoluminescence (PL) degradation studies showed that the phosphor intensity decreased about 20% over a period of 2 weeks under ultraviolet (UV) irradiation. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) showed that cathodoluminescence (CL) degradation is due to the formation of SrO due to electron stimulated surface reactions. The light output mechanism of the phosphor is also discussed in more detail.     

The influence of the number of pulses on the morphological and photoluminescence properties of SrAl2O4:Eu,Dy thin films prepared by pulsed laser deposition

The current work reports on the influence of the number of laser pulses on the morphological and photoluminescence properties of SrAl₂O₄:Eu²⁺,Dy³⁺ thin films prepared by the pulsed laser deposition (PLD) technique. Atomic force microscopy (AFM) was used to study the surface topography and morphology of the films. The AFM data showed that the film deposited using a higher number of laser pulses was packed with a uniform layer of coarse grains. In addition, the surface of this film was shown to be relatively rougher than the films deposited at a lower number of pulses. Photoluminescence (PL) data were collected using the Cary Eclipse fluorescence spectrophotometer equipped with a monochromatic xenon lamp. An intense green photoluminescence was observed at 517 nm from the films prepared using a higher number of laser pulses. Consistent with the PL data, the decay time of the film deposited using a higher number of pulses was characteristically longer than those of the other films. The effects of laser pulses on morphology, topography and photoluminescence intensity of the SrAl₂O₄:Eu²⁺,Dy³⁺ thin films are discussed.     

Luminescent properties of SrAl2B2O7: Ce, Tb

By using metal nitrates as starting materials, SrAl₂B₂O₇: Tb³⁺ and SrAl₂B₂O₇: Ce³⁺, Tb³⁺ powder phosphors were prepared by sol-gel method. X-ray diffraction (XRD), photoluminescence excitation and emission, as well as kinetic decays were employed to characterize the resulting samples. The results show that energy transfers from Ce³⁺ to Tb³⁺ ions. The emission intensity of Tb³⁺ ions in SrAl₂B₂O₇ could be greatly intensified when Ce³⁺ ions are doped into SrAl₂B₂O₇: Tb³⁺. The decay times of SrAl₂B₂O₇: Tb³⁺ were prolonged when Ce³⁺ ions were doped. The doping of Ce³⁺ ions not only improved the luminescent intensity, but also made the materials gets stable luminescent properties.     

Emission analysis of Li6LuY(BO3)3:Tb3+,Dy3+ phosphors

In this paper, we present the synthesis and luminescence properties of Tb³⁺ and Dy³⁺-doped lithium lutetium yttrium borate (Li₆LuY(BO₃)₃) phosphors. We have adopted the well-known solid state reaction method for the synthesis of these phosphors. The emission intensities of the synthesized phosphors were found to reach their maximum, when doped by 1 mol% of Tb³⁺ and 3 mol% of Dy³⁺, beyond which emission intensities decrease due to concentration quenching. The homogeneous phase, crystalline structure and uniform morphology of the synthesized phosphors were confirmed by X-ray diffraction analysis (XRD) and Scanning electron microscopy (SEM). The X-ray and UV–VIS-induced luminescence, decay time and CIE chromaticity were investigated for the synthesized phosphors.The X-ray induced integrated light yield was measured to be 82% for Li₆LuY(BO₃)₃:Tb³⁺ (LLYBO) and 59% for Li₆LuY(BO₃)₃:Dy³⁺ of that of commercially available X-ray imaging material; Gd₂O₂S:Tb³⁺ (Gadox).LLYBO:Tb³⁺ phosphor displayed five major emission bands that correspond to ⁵D_j → ⁷F_j transitions. The 1931 Commission Internationale de l'Eclairage (CIE) chromaticity coordinates were also measured.     

Optical properties of Sm3+ and Dy3+ ions in Gd2MoB2O9 host lattice

Gd₂MoB₂O₉ doped with Sm³⁺ and Dy³⁺ were used for this study. The photoluminescence behaviors of Sm³⁺ and Dy³⁺ in this phosphor material were investigated by the excitation and emission spectra. The Sm³⁺-doped Gd₂MoB₂O₉ phosphor powders show a red luminescence, whereas the Dy³⁺-doped Gd₂MoB₂O₉ phosphor powders show a yellow luminescence. In addition, the optimum doping concentration and the time-resolved luminescence spectroscopy were also investigated.     

Photoluminescence and phosphorescence properties of MAl2O4:Eu, Dy (M=Ca, Ba, Sr) phosphors prepared at an initiating combustion temperature of 500 °C

Eu²⁺ and Dy³⁺ co-doped calcium aluminate, barium aluminate and strontium aluminate phosphors were synthesized at an initiating combustion temperature of 500 °C using urea as an organic fuel. The crystallinity of the phosphors was investigated by using X-ray diffraction (XRD) and the morphology was determined by a scanning electron microscope (SEM). The low temperature monoclinic structure for both CaAl₂O₄ and SrAl₂O₄ and the hexagonal structure of BaAl₂O₄ were observed. The effect of the host materials on the photoluminescence (PL) and phosphorescence properties were investigated by using a He-Cd Laser and a Cary Eclipse fluorescence spectrophotometer, respectively. The broad band emission spectra observed at 449 nm for CaAl₂O₄:Eu²⁺, Dy³⁺, 450 nm (with a shoulder-peak at 500 nm) for BaAl₂O₄:Eu²⁺, Dy³⁺ and 528 nm for SrAl₂O₄:Eu²⁺, Dy³⁺ are attributed to the 4f⁶5d¹ to 4f⁷ transition in the Eu²⁺ ion in the different hosts.     

White light emission from sonochemically synthesized rare earth doped ceria nanophosphors

Undoped CeO₂, and single and triple doped CeO₂:M (where M=Dy³⁺, Tb³⁺and Eu³⁺) nanophosphors were synthesized through a simple sonochemical process and characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), EDS and photoluminescence (PL) spectrophotometry. The TEM micrographs show that resultant nanoparticles have flower-like shape. The doped samples showed multicolor emission on single wavelength excitation. Energy transfer was observed from host to the dopant ions. Characteristic blue emission from Dy³⁺ ions, green from Tb³⁺ ions and red from Eu³⁺ ions were observed. The CIE coordinates of the triple doped Ce_0.86Dy_0.005Tb_0.055Eu_0.08O₂ nanoflowers lie in the white light region of the chromaticity diagram and show promise as good phosphor materials for new lighting devices.     

Synthesis and characterization of monodisperse spherical core-shell structured SiO2@Y3Al5O12:Ce3+/Tb3+ phosphors for field emission displays

Nanocrystalline Y₃Al₅O₁₂: Ce³⁺/Tb³⁺ (average crystalline size 30 nm) phosphor layers were coated on non-aggregated, monodisperse and spherical SiO₂ particles by the sol-gel method, resulting in the formation of core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles. X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ phosphor particles. The obtained core-shell structured phosphors consist of well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ shells on the SiO₂ cores (average size about 500 nm, crystalline size about 30 nm) could be easily tailored by varying the number of deposition cycles (100 nm for four deposition cycles). Under the excitation of ultraviolet and low-voltage electron beams (1–3 kV), the core-shell SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles show strong yellow-green and green emission corresponding to the 5d–4f emission of Ce³⁺ and ⁵D₄–⁷F _J (J = 6, 5, 4, 3) emission of Tb³⁺, respectively. These phosphors may have potential application in field emission displays.     

Morphology and crystalline-phase-dependent luminescence of Li-doped Gd2O3:Eu3+ thin films grown by pulsed laser deposition

Gd₂O₃:Eu³⁺ and Li-doped Gd₂O₃:Eu³⁺ luminescent thin films have been grown on Si(100) substrates using pulsed laser deposition. The films grown at different deposition conditions show different crystalline and morphology structures and luminescent characteristics. Although both cubic and monoclinic crystalline structures were observed in both Gd₂O₃:Eu³⁺ and Li-doped Gd₂O₃:Eu³⁺ films, the cubic structure becomes more dominant for Li-doped Gd₂O₃:Eu³⁺ films. The photoluminescence brightness data obtained from Li-doped Gd₂O₃:Eu³⁺ films indicate that Si(100) is a promising substrate for growth of high-quality Li-doped Gd₂O₃:Eu³⁺ thin-film red phosphor. In particular, the incorporation of Li⁺ ions into the Gd₂O₃ lattice induced a change of crystallinity and enhanced surface roughness. Two major factors to determine photoluminescence brightness for Li-doped Gd₂O₃:Eu³⁺ films were crystalline phase and surface roughness. The highest emission intensity was observed with Gd_1.84Li_0.08Eu_0.08O₃, whose brightness was a factor of 2.1 larger than that of Gd₂O₃:Eu³⁺ films. This phosphor is promising for applications in flat-panel displays. PACS 78.20.-e; 78.55.-m; 78.66.-w     

The effect of oxygen pressure on the structure, morphology and photoluminescence intensity of pulsed laser deposited Gd2O2S:Tb3+ thin film phosphor

Luminescent Gd₂O₂S:Tb³⁺ phosphor thin films were grown on Si (100) substrates, using the pulsed laser deposition technique. The films were grown in 100 to 300 mTorr oxygen gas (O₂) atmospheres when the substrate temperature was kept constant at 400 or 600°C. The effect of the O₂ ambient on the structure and morphological properties of the films were analyzed using x-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. Spherical nanoparticles deposited on the Si (100) substrates were shown to crystallize in the hexagonal structure of Gd₂O₂S. The photoluminescence (PL) spectra of all the films were characterized by a stable green emission peak with a maximum at 545 nm. Improved PL intensity was observed from the films deposited at higher oxygen pressures and higher substrate temperatures. Particles sizes of the nanoparticles deposited under the different conditions varied between 19 and 36 nm for the different samples. Smaller and more densely packet particles were produces at the higher O₂ pressures and the higher temperature.     

Synthesis and luminescence properties of SrAl2O4:Eu,Dy nanosheets

We report an effective method to synthesize SrAl₂O₄:Eu²⁺,Dy³⁺ nanosheets. Sheet-like precursors were firstly synthesized by the solvothermal method, and acetate was used as the raw material. Then the final products were obtained by calcinating the precursor in a weak reductive atmosphere of H₂. The crystal structure and particle morphology were investigated by X-ray diffraction (XRD) patterns, field-emission scanning electron microscopy and transmission electron microscopy (FE-SEM and TEM) , respectively. A possible growth mechanism was proposed to reveal the formation process. Luminescence properties of the SrAl₂O₄:Eu²⁺,Dy³⁺ long-lasting phosphor were analyzed by measuring the excitation spectra, the emission spectra, the afterglow decay curve and the thermoluminescence curve. Both the photoluminescence (PL) spectra and luminance decay revealed that the phosphors had efficient luminescent and long lasting properties compared with the phosphors prepared by using nitrates as the raw material. Furthermore, the photoluminescence intensity was even a little higher than commercial phosphors.     

Synthesis and luminescence properties of needle-like SrAl2O4:Eu, Dy phosphor via a hydrothermal co-precipitation method

Needle-like SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors had been prepared by calcining the precursors obtained from hydrothermal process at the temperature of 1100 °C in a weak reductive atmosphere of active carbon. The crystal structure, morphology and optical properties of the composites were characterized. X-ray diffraction (XRD) patterns illustrated that the single-phase SrAl₂O₄ was formed at 1100 °C, which is much lower than that prepared by the traditional method. The transmission electron microscope (TEM) observation revealed the precursors and the resulted SrAl₂O₄:Eu²⁺, Dy³⁺ phosphors had well-dispersed distribution and needle-like morphology with an average diameter about 150 nm at the center and the length up to 1 μm. After irradiation by ultraviolet radiation with 350 nm for 5 min, the phosphors emit green color long-lasting phosphorescence corresponding to the typical emission of Eu²⁺ ion, both the PL spectra and luminance decay revealed that the phosphors had efficient luminescent and long lasting properties.     

Enhanced luminescence and degradation of SiO2:Ce,Tb powder phosphors prepared by a sol-gel process

Enhanced green photoluminescence and cathodoluminescence (CL) from Tb³⁺ ions due to co-doping with Ce³⁺ ions were observed from SiO₂:Ce,Tb powder phosphors prepared by a sol-gel technique. Blue emission from the Ce³⁺ ions was completely suppressed by Tb co-doping, presumably due to energy transfer from Ce³⁺ to Tb³⁺. In addition, the green CL intensity from SiO₂:Ce,Tb degraded by ∼50% when the powders were irradiated for 10 h with a 2 keV, 54 mA/cm² beam of electrons in an ultra-high vacuum chamber containing either 1×10⁻⁸ or 1×10⁻⁷ Torr O₂. Desorption of oxygen from the surface was observed during the decrease of CL intensity. The mechanisms for energy transfer from Ce³⁺ ions to Tb³⁺ ions to enhance the green luminescence, and mechanisms for desorption of oxygen from the phosphor surface that would result in decreased CL intensity are discussed.     

Surface characterization and luminescent properties of SrAl2O4:Eu,Dy nano thin films

SrAl₂O₄:Eu²⁺, Dy³⁺ thin films were grown on Si (1 0 0) substrates in different atmospheres using the pulsed laser deposition (PLD) technique. The effects of vacuum, oxygen (O₂) and argon (Ar) deposition atmospheres on the structural, morphological and photoluminescence (PL) properties of the films were investigated. The films were ablated using a 248 nm KrF excimer laser. Improved PL intensities were obtained from the unannealed films prepared in Ar and O₂ atmospheres compared to those prepared in vacuum. A stable green emission peak at 520 nm, attributed to 4f⁶5d¹→4f⁷ Eu²⁺ transitions was obtained. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The diffusion of adventitious C into the nanostructured layers deposited in the Ar and O₂ atmospheres was most probably responsible for the quenching of the PL intensity after annealing.     

Hydrothermal synthesis,characterization, and luminescence of Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>:RE (RE = Eu<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript>, Dy<Superscript>3+</Superscript>) nanofibers

Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were synthesized by the hydrothermal reaction method. The structural refinement was conducted on the base of the X-ray powder diffraction (XRD) measurements. The surface properties of the Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were investigated by the measurements such as the scanning electron microscope (SEM), transmission electron microscope (TEM), and the energy dispersive spectrum (EDS). The nanofiber has a diameter of about 100 nm and a length of several micrometers. The luminescence properties such as photoluminescence excitation (PLE) and emission spectra (PL), decay lifetime, color coordinates, and the absolute internal quantum efficiency (QE) were reported. Ca₂B₂O₅:Eu³⁺ nanofibers show the red luminescence with CIE coordinates of (x = 0.41, y = 0.51) and the luminescence lifetime of 0.63 ms. The luminescence of Ca₂B₂O₅:Tb³⁺ nanofibers is green color (x = 0.29, y = 0.53) with the lifetime of 2.13 ms. However, Dy³⁺-doped Ca₂B₂O₅ nanofibers present a single-phase white-color phosphor with the fluorescence decay of 3.05 ms. Upon near-UV excitation, the absolute quantum efficiency is measured to be 65, 35, and 37 % for Eu³⁺-, Tb³⁺-, Dy³⁺-doped Ca₂B₂O₅ nanofibers, respectively. It is suggested that Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers could be an efficient phosphor for lighting and display.     

Sensitized luminescence through nanoscopic effects of ZnO encapsulated in SiO2:Tb sol gel derived phosphor

Terbium (1 mol%) doped ZnO-SiO₂ binary system was prepared by a sol-gel process. Nanoscopic effects of ZnO on the photoluminescence (PL) and the cathodoluminescence (CL) properties were studied. Defects emission from ZnO nanoparticles was measured at 560 nm and the line emission from Tb³⁺ ions in SiO₂:Tb³⁺ and ZnO-SiO₂:Tb³⁺ with a major peak at 542 nm was measured. The PL excitation wavelength for 542 nm Tb³⁺ emission was measured at ∼320 nm in both SiO₂:Tb³⁺ and ZnO-SiO₂:Tb³⁺. The CL data showed quenched luminescence of the ZnO nanoparticles at 560 nm from a composite of ZnO-SiO₂:Tb³⁺ and a subsequent increase in 542 nm emission from the Tb³⁺ ions. This suggests that energy was transferred from the ZnO nanoparticles to enhance the green emission of the Tb³⁺ ions. The PL and CL properties of ZnO-SiO₂:Tb³⁺ binary system and possible mechanism for energy transfer from the ZnO nanoparticles to Tb³⁺ ions are discussed.