Barium thioaluminate with europium (BaAl2S4:Eu) is the most efficient blue light-emitting material in inorganic thin-film electroluminescent devices. In order to fabricate full-color electroluminescent devices, blue light-emitting layers were prepared in several ways. Single target sputtering deposition is one of the effective methods for preparing blue luminescent layers. In this paper, a new structural target material is introduced and its preparation process is studied. The photoluminescence spectra of the prepared target showed that the two kinds of luminescent layers doped with europium at 3mol% and 5mol% had blue emission characteristics. The emission peaks of the UV-excited photoluminescence spectra at 290nm, 300nm and 320nm were all near 470nm. Therefore, the prepared target can be used for single target sputtering deposition of BaAl2S4:Eu thin films. XRD results showed that there were four different phases in Target 1: Barium tetraaluminium sulfide (BaAl4S7), barium sulfide (BaS) , europium sulfide (EuS) and barium aluminum oxide (BaAl2O4). In addition to these four phases, two other phases were detected in Target 2: Aluminum Sulphide (Al2S3) and barium thioaluminate (BaAl2S4). The results showed that Target 1 was more suitable for sputtering BaAl2S4:Eu thin films due to the hydrolysis of Al2S3. XPS and X-ray fluorescence spectra reflected the exact molar ratios of each element. In Target 1, the relative atomic concentration of Ba, Al, S and O was about 9:33:41:17. The molar ratio of barium to europium was about 1:0.03. In conclusion, Target 1 was more suitable for preparing blue light-emitting layers in inorganic electroluminescent devices.
Europium-doped barium thioaluminate (BaAl2S4:Eu) is currently the most efficient blue phosphor for inorganic thin film electroluminescent (iEL) device. To produce the full-color EL device, several kinds of blue-emitting layer were attempted and tested. As a key point of blue-emitting layer fabrication, single target sputtering deposition is an effective method. In this work, new structural target is introduced and the fabricated process is expatiated. The PL spectra of as fabricated targets show that both of two, 3mol% and 5mol% europium-doped, have blue emitting property. According to the PL spectra excited by 290nm, 300nm and 320nm ultraviolet, emission peaks located in the region near 470nm. So the as-fabricated targets can be used in single target sputtering deposition on thin film of BaAl2S4:Eu. XRD pattern indicates that there are 4 different phases, barium tetraaluminum sulfide (BaAl4S7), barium sulfide (BaS), europium sulfide (EuS) and barium aluminum oxide (BaAl2O4), in target 1. Besides these four compounds, other two phases, aluminum sulfide (Al2S3) and barium thioaluminate (BaAl2S4), are detected in target 2. Considering the analysis results, especially the hydrolyzation of Al2S3, target 1 is more suitable for sputtering deposition of BaAl2S4:Eu thin film. XPS and X-ray Fluorescence patterns describe the precise molar ratio of each element. In target 1 the relative atom concentration of barium, aluminum, sulfur and oxygen can be calculated from the pattern and molar ratio is about 9:33:41:17. Molar ratio of barium and europium is about 1:0.03. In short, the barium thioaluminate doped by europium sputtering target 1 is better to be applied in the fabrication of blue-emitting layer in inorganic electro-luminescent devices.
As novel Liquid Crystal Display (LCD) materials, blue phase liquid crystalline polymers have attracted considerable attention and interests, mainly because of their unique properties, including wide angle of view, fast response times and selective reflection of light. Blue phases are mesophases usually exhibited by highly chiral materials and commonly occur in a narrow temperature range below the isotropic phase.They are optically active and non-birefringent, while exhibit Bragg diffraction of light in the visible wavelength. So they can improve and enhance the performances of liquid crystal display in manned spacecraft. The development and recent advances are reviewed with a brief introduction of the history of the blue phase studies. Some special properties are analyzed especially the frustration in the double twist molecular alignment. The application prospect of blue phase liquid crystalline polymers in manned spacecraft are discussed. Because of high resolution, high response speed, low power, low weight and small footprint, blue phase liquid crystal displays can meet the technique requirements on displays in our future manned spacecrafts, especially space station. Blue phase liquid crystalline polymers have more superior performances on viewing angle. Thus, blue phase LCD is a better choice to improve the viewing angle in manned spacecrafts.
Europium doping barium thioaluminates thin films are sputtered by Al complex target embedded with BaS:Eu pellets
sintered by spark plasma sintering (SPS). Thin films are deposited by RF-sputtering with complex target. BaAl2S4 is found in each thin film sample while BaAl4S7 appears in the samples only if the amount of BaS:Eu pellets is more than 3. Oxidizing products are BaAl2O4, BaSO4 and Al2O3. The amounts of barium thioaluminates including BaAl2S4 and BaAl4S7 will increase while the one of Al2O3 and BaS decrease if more BaS:Eu pellets are embedded in the target during
sputtering. Elements analysis is carried out by EDS. The Al/Ba ratio in thin films will approach 2.0 with more pellets
existing in target. PL spectra of thin films are measured and analyzed. The most obvious emission peak in each spectrum
is located at about 470nm which corresponds to the 4f65d1→4f7 transition of Eu2+ in BaAl2S4 lattice. The emission peak will approach 470nm as more pellets are embedded in complex target. As a result, it can be concluded that increasing the amounts of BaS:Eu pellets in complex target is an efficient way to achieve better Eu doping barium thioaluminates thin film.
The luminescent properties of different MIIxMII1-xAl2S4:Eu and MIIAl2S4:Eu are researched in this paper. A novel
assessment method is used to evaluate these materials base on the configuration coordinates model. Vibronic coupling
parameters of these phosphor materials can be calculated by the formula. With the calculation of characteristic energy
and unitless factors, performances of MIIxMII1-xAl2S4:Eu and MIIAl2S4:Eu are evaluated. We then concluded that
BaAl2S4:Eu shows highest Φ value comparing with other single or complex thioaluminates. With increasing amounts of
Ba and Ca ions in the BaxMg1-xAl2S4:Eu and Ca1-ySryAl2S4:Eu respectively, the complex thioaluminates gives better
luminescent performance and a broad tunable emission color can be achieved.
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