以固相法製備矽基與鋰鋁基氮氧化物螢光粉

Preparation of silicon-based and lithium aluminum-based oxynitride phosphors by solid-phase synthesis

洪傑瑞(Jie-Ruei Hung)

指導教授 ： 林炯棟

義守大學/理工學院/材料科學與工程學系/碩士(2016年)

摘要

為了改善目前白光LED 所面臨的色溫過低與熱穩定不佳問題，本論
文針對黃色螢光粉Ca-α-SiAlON:Eu2+與可在低溫合成的鋰鋁基螢光粉的製備與其發光特性進行研究。
本研究分為兩部份，第一部分利用高溫固相法製備矽基氮氧化物螢光材料，探討添加碳粉、溫度變化、銪濃度、鈣矽比、矽鋁比、鈣源變
化以及通入氮氫氣體氣氛流量其對顯微結構與發光特性的影響。第二部
分則以固態反應法來製備銪摻雜鋰鋁基之氮(氧)化物，改變煆燒溫度
(1000°C 至1350°C)、持溫時間與氣體流量，探討對顯微結構與發光特性的影響。
首先XRD 結果顯示，碳粉的添加有助於β-SiAlON 相的生長，而對發光特性無明顯助益。從SEM 圖中發現，摻雜2%氧化銪在溫度1620℃時煆燒6 小時顆粒大小大約5μm，濃度提升至4%時出現棒狀顆粒，棒狀顆粒是由顆粒向外長出;但當摻雜濃度提升到8%時，棒狀消失而呈現熔融狀，推斷與摻雜Eu 濃度提升而促使晶粒改變。於460nm 激發光源下，於580-585nm 之發光強度是隨銪濃度之增加而提高，當濃度提高時會產生了紅移的現象。在不同溫度條件下煆燒6 小時後發現，以1620℃煆燒者其發光強度最高，當溫度下降至1470℃後發現存在殘留的氮化矽、氮化鋁與碳酸鈣的相，溫度的不足造成了反應不完全，進而造成發光性能下降。
其次，改變氮氫氣體的進氣流量(100sccm~300sccm)，當逆流閥達一定
壓力(0.86kPa)時會排出氣體，此時可能會與外面的空氣接觸。摻雜8%
Eu2O3 之 Ca-α-SiAlON:Eu2+在1620℃下煆燒6 小時之螢光粉，當流量下降或上升時，XRD 圖並無明顯差異。以流量為200sccm 之發光強度最高，不過，當流量提升至300sccm 時，發現產生了紅移的現象。
進一步改變矽鋁比(1、2、3、4)，矽鋁比為1 時，並無法形成Ca-α-SiAlON相，當矽鋁比提高至3 以上， Ca0.8Si9.2Al2.8O1.2N14.8 相為主要結晶相，於460nm 激發光源下，其於581nm-586nm 為主要的發射峰。發光強度之順序為：Si/Al=2＞Si/Al=3＞Si/Al=4＞Si/Al=1，且Si/Al=4 產生了明顯的藍移現象。若將鈣鋁比提高至1.5 倍反而使發光強度下降，這說明提升鈣量並無幫助。而將鈣源換為氫化鈣後，在XRD 圖中出現了β-SiAlON 相，且銪摻雜濃度越高，繞射峰強度越強，氫化鈣與濃度越高的銪可能會促使β-SiAlON 的形成。Ca-α-SiAlON 系統進行熱粹滅測量後發現從30℃上升至到180℃，發光強度下降至原來的90%-92%左右，Ca-α-SiAlON 系統具有良好的熱穩定性，矽鋁比與鈣鋁比對熱穩定性並無明顯影響。摻雜8%氧化銪Ca-α-SiAlON 在TEM /EDS 成分分析中發現在1470℃時氧的含量最低，當溫度提高至1620℃後氧的比例明顯增加。
而在製備鋰鋁基摻雜銪之氮(氧)化物方面，結果顯示當煆燒溫度降低且流量增高時其發光強度會提高，當溫度提高時會造成鋰的流失，因為含鋰結晶相為發射紅光的主要基質(host)，特別值得注意的是其放射光617nm 之半高寬僅為∼60 nm 。

關鍵字

螢光粉 ； 氮氧化物 ； 白光發光二極體 ； 窄帶螢光粉

並列摘要

In order to improve the color temperature and thermal stability of current white LED, the yellow-emitting Ca-α-SiAlON:Eu2+ phosphors and red-emitting lithium-aluminum-based oxynitride phosphors were prepared by solid state
synthesis. The thesis is divided into two parts, the first part discussed about the high temperature solid state synthesis of Ca-α-SiAlON:Eu2+ oxynitride phosphors, the effect of carbon addition, calcination temperature changes, concentration of europium, silicon to aluminum ratio, calcium source and flow rate of N2-H2 atmosphere on the luminescent charachersitics and microstructures were further studied in details. Subsequently, the second part considered about that the solid state reaction method was used to prepare the europium-doped lithium aluminum oxynitride phosphors by changing the calcination temperature (1000 °C to 1350 °C), holding time and gas flow rate, and the relationship between microstructure
andluminescent characteristics were also explored.
At first, XRD results showed that carbon addition can help the growth of β-SiAlON phase, but the emission strength tended to reduce. From the SEM image, after calcination at 1620℃ for 6hrs, the particle size of phosphors doped with 2% Eu2O3 was about 5μm. When Eu2O3 dopant was increase to 4%, the rod-like particles are observed; once further raised to 8%, rods disappeared and particles begun to occur molten phenomenon. Under a 460nm excitation, the emission intensity at 580-585nm and red shift is increased with the europium concentration.
It was found that phosphors after 1620 ℃ calcination exhibited the highest emission intensity. When the temperature dropped to 1470 ℃, the presence of residual silicon nitride, aluminum nitride and calcium carbonate phase resulted in the poor emission due to incomplete reaction.
Secondly, the air flow rate of nitrogen hydrogen gas (100sccm ~ 300sccm) also influenced the characteristic of Ca-α-SiAlON: Eu2 +, it may be due to the fact the
reflux valve reached a certain pressure (0.86kPa) and gas is discharged, raw materials may be in contact with the outside air during this period. For the Ca-α-SiAlON: Eu2 + phosphors doping with 8% Eu2O3 after calcination at 1620 ℃ for 6hrs, when the flow rate changed, there was no significant difference in the XRD patterns. However, the PL results indicated that 200 sccm yielded the highest luminous intensity, when the flow rate increased to 300 sccm , red shift was observed in emission spectrum.
Furthermore, the effect of Si/Al ratio (1,2,3,4) were explored. As Si/Al ratio was 1, and it can not form Ca-α-SiAlON phase. The Si/Al ratio increased to more than 3, Ca0.8Si9.2Al2.8O1.2N14 .8 phase was the main crystalline phase and phosphors exhibited a emission peak at 581nm-586nm under a 460nm excitation. The orde of luminous intensity of phosphors is : Si / Al = 2> Si / Al = 4> Si / Al = 3> Si / Al = 1, and the Si / Al = 4 had a significant blue shift. In addition, calcium aluminum ratio increased to 1.5 times but to make the emission intensity decrease, indicating that the increase of Ca did not enhance the PL intensity. When calcium hydride was used as Ca source, XRD patterns revealed the existence of β-SiAlON phase. The higher the Eu concentration, the stronger the intensity of the diffraction peak for β-SiAlON phase. And the higher concentration of europium could promote β-SiAlON phase
formation. The thermal quenching of Ca-α-SiAlON system was measured from 30℃ to 180 ℃, the emission intensity dropped to about the original 90%-92%, it can conclude that Ca-α-SiAlON system had good thermal stability. The Si/Al ratio and Ca/Al ratio had no significant effect on the thermal stability. The oxygen content of Ca-α-SiAlON doped 8% Eu2O3 showed the lowest value at 1470 ℃ and significantly increased when the temperature raised to 1620 ℃.
For the Eu-doped lithium aluminum based oxynitrides, the results showed that when the calcination temperature and the flow rate increased, its emission intensity increased. The increase of temperature would cause the loss of lithium. The lithium-containing crystalline phase exhibited red emission, the half-width of emission peak at 617nm was only ~60 nm.

並列關鍵字

oxynitride phosphors ； white light emitting diodes ； β-SiAlON ； Ca-α-SiAlON ； narrow-band

參考文獻

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