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Preparation and Photoluminescent Characteristics of Strontium Orthosilicate and Strontium Aluminate Phosphors
phosphor,strontium silicate,strontium aluminate,
|Publication Year :||2006|
矽酸鍶摻雜銪離子 (Sr2SiO4: Eu2+) 粉體為LED所需新型且重要之螢光粉體，在UV/ Blue區間寬廣的吸收帶。本研究以固相法，固定不同成分之計量比，添加不同顆粒大小SiO2為起始物，進行高溫還原反應，發現隨著添加粒徑較小之起始物SiO2，螢光強度增加，且發光波長往長波長方向移動。當掺雜相同大小粒徑SiO2，發現鍛燒時間縮短時，造成放光波長亦會往長波長方向移動。推測是由於Eu2+離子間距離較短，造成晶場強度改變，4f65d1外層的5d電子軌域分裂，引發非輻射能量傳遞增加，輻射能量減少，造成的放射峰的紅移。
鋁酸鍶摻雜銪，鏑離子之長餘暉螢光粉體 (SrAl2O4: Eu2+, Dy3+ ) 為新一代長餘暉夜光材料，在UV/ Blue區間有寬廣的吸收帶，放射出綠光。本研究利用溶膠-凝膠法，成功以在1300oC煆燒四小時，合成出單相鋁酸鍶粉體，放射光譜呈現一寬廣的峰，最高峰位置落在524 nm，這是由於Eu2+置換Sr2+位置，經由f-d能階轉換 (4f65d1→ 4f7) 所造成。由SEM照片得知，合成出的粉體為粒徑約0.6μm，分散均勻的粉體。本研究改變溶液pH值，發現pH值在7.0的時候，粉體有最強的螢光強度，且餘暉時間亦隨著pH值增加而增長。推測是pH值改變檸檬酸與金屬離子螯合的程度所造成的差異，由平衡常數計算出的模型，可以支持這項推測。
The field of luminescence material is a promising industry, and the government pays much attention on it. LED and afterglow phosphors are widely applied and were discussed in this thesis.
Strontium orthosilicate (Sr2SiO4: Eu2+) is a new type phosphor. Sr2SiO4: Eu2+ provides the broadband absorption in UV/ Blue region and results in a strong yellow emission. In this study, the phosphors were synthesized via solid-state reaction by using silica with different particle sizes. It was found that the luminescent intensity increased and the red shift occurred in wavelength from 570 nm to 590 nm with using small silica. Additionally, when silica with the same particle size was used, the blue shift of emission happened with increasing reaction time. The above behavior is because the decrease of distance between Eu2+ ions leads to the changes of the crystal field around Eu2+ ions. The 4f electrons of Eu2+ are insensitive to a lattice environment due to the shielding function of the electrons in the outer shell, the 5d electrons split by the crystal field, which lead to the increase of non-radiative energy transferring between Eu2+ ions. Therefore, the radiative energy decreases and the wavelength of emission has a red shift.
Strontium aluminates doped europium and dysprosium ions (SrAl2O4: Eu2+, Dy3+) phosphor is a new type of afterglow phosphor. This phosphor provides a broad band absorption in UV/ blue region, and emits green light. A sol-gel process employing citric acid and ethylene glycol as polymerizing agent was developed for synthesizing strontium aluminates phosphors. From SEM analysis, it was found the particles were dispersed well and the grain was around 0.6μm. A broad band was obtained on the emission spectrum and the peak at about 524 nm is attributed to the f-d transition of Eu2+ ions, substituting Sr2+ ions in the host. In the research, the pH value of the solution was adjusted in sol-gel method, and it was found that the highest intensity of emission was obtained at the pH value was equal to 7.0. Additionally, the lifetime increased with increasing pH values. It was proved that the extent of chelation between citrate ions and metal ions influenced by pH value through the calculation from critical stability constants.
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