- 學位論文
(Y1-x-yPrxLay)InGe2O7 (x=0~0.2, y=0~0.2)系之光致發光特性研究
Synthesis and Photo-Luminescence Properties of (Y1-x-yPrxLay)InGe2O7 (x=0~0.2, y=0~0.2) Phosphors
摘要
本研究是利用固態反應法製備鍺酸鹽類作為螢光粉主體，添加稀土金屬元素Pr3+離子當作發光中心並共摻La3+離子，所合成Y1-x-yLayPrxInGe2O7螢光粉體，探討其摻雜濃度對粉體型態、晶體結構和發光特性之影響。 於YInGe2O7摻雜Pr3+螢光粉系列，由XRD結果顯示，在煆燒溫度1200°C持溫10小時的條件下，可以得到單斜晶系YInGe2O7之結晶結構，而螢光粉體表面形態並不會因Pr3+離子摻雜濃度之多寡而有所影響。在Y1-xPrxInGe2O7螢光粉粉體中，光致發光有兩種機制：(一)間接激發發光；(二)直接激發發光。在263 nm紫外光源激發下，其放射光譜由主體本身發光及Pr3+離子的3P0→3H4,5,6和1D2→3H4電子躍遷所構成，發光帶分佈於350 ~ 480 nm、480 ~ 520 nm、530 ~ 570 nm、580 ~ 620 nm、620 ~ 650 nm範圍中。當摻雜Pr3+離子濃度達0.2 mol%時，可達最佳的發光強度，呈現白光放射，其CIE色度座標為(x=0.321，y=0.286)；而以452 nm 藍色光源激發下，其放射光譜主要強烈發光帶為480 ~ 520 nm，為Pr3+離子的3P0→3H4電子躍遷，當摻雜Pr3+離子濃度達5 mol%時，可達最佳的發光強度，呈現綠光放射，其CIE色度座標為(x=0.168，y=0.499)。 另外在YInGe2O7：Pr,La螢光粉體系列中，固定Pr3+離子濃度為0.2 mol%的情況下，共摻不同濃度的La3+離子導致Pr3+離子所處晶格環境進而改變其發光性質。在激發波長263 nm 激發下，從放射光譜顯示，隨著La3+離子添加量的提高，發光峰位於604 nm強度為最強，則屬於Pr3+離子的1D2→3H4電子躍遷，從而得知共摻La3+離子，使晶格膨脹變大，但局部Pr-O是受到壓縮的鍵長反而縮短，Pr3+離子受到較強的晶格場作用，Pr3+離子之f-d能階分裂變大，其組態座標縱移到更低能量較接近1D2能階，電子以非輻射能量有效的轉移至1D2能階，而使1D2→3H4躍遷發光強度亦較高。其中在La3+離子濃度為10 mol%時，可獲得最佳的發光強度。而CIE座標為(x=0.408，y=0.330)，其發光顏色則往暖白光區域移動，從(x=0.321，y=0.286)至(x=0.408，y=0.330)。 由XPS光譜圖顯示，在Y0.998Pr0.002InGe2O7：La3+螢光粉體中，當La3+離子濃度為10 mol%時，氧空缺之數目開始增加，發光強度反而為最強，是由於適量的氧空缺可作為增感劑促進能量轉移，進而提升發光強度。但當濃度超過10 mol%之後，氧空缺數目持續增加，發光強度開始降低，是因為過量之La3+離子摻雜造成晶格的拉應變增大，及晶格扭曲程度增加，導致雜相的產生，因此主體中存在過多的氧空缺，而這些位置可能成為毒劑或淬滅中心，導致能量耗損使發光效率下降。
並列摘要
In this study, YInGe2O7 germanate phosphor was selected as the host material. Pr3+ and La3+ ions co-doped YInGe2O7 phosphor were synthesized using a vibrating milled solid state reaction with metal oxides and calcined at 1200 °C for 10 h in air. The crystal structure, surface morphologies, and photoluminescence properties of the Y1-x-yPrxLayInGe2O7 phosphors were then investigated. For Pr3+ ion-doped YInGe2O7 phosphors, the XRD patterns show that all of the peaks are attributed to the monoclinic YInGe2O7 phase as the Pr3+ ions doped. The FE-SEM results show that there are no obvious differences for surface morphology of Pr3+-doped YInGe2O7 phosphors. There are two photoluminescence mechanisms for Y1-xPrxInGe2O7 phosphors: (a) host-activator transition, and (b) direct excitation of Pr3+ ion. By UV light 263 nm excitation, the emission spectra of (Y1-xPrx)InGe2O7 phosphors show a broad band between 350 to 480 nm, which is attributed to the emission of the YInGe2O7 host. A series of sharp emission peaks at 503, 530, 604 and 646 nm are assigning to the 3P0→3H4, 3P0→3H5, 1D2→3H4, 3P0→3H6 transition of Pr3+ ions, respectively. The optimal PL intensities is obtained for YInGe2O7 doped with 0.2 mol% Pr3+ ions, which has a CIE chomaticity coordinates of (x=0.321，y=0.286) located in the white region. Furthermore, under an excitation of 452 nm, the emission spectra of (Y1-xPrx)InGe2O7 phosphors show a dominant green emission peak at 503 nm, which is due to the 3P0→3H4 transition. The optimal PL intensity is obtained when the Pr3+ ion concentration is 5 mol%, and which is located in the green region with a CIE chomaticity coordinates of (x=0.168，y=0.499). In addition, in order to enhance the photoluminescence properties of YInGe2O7:Pr3+ phosphors, the La3+ ion is introduced to substitute Y3+ ion, and change thee lattice symmetry of Pr3+ ion as the Pr3+ ion concentration is fixed for 0.2 mol%. The emission spectra of (Y0.998-yLayPr0.002)InGe2O7 phosphors show a maximum intensity of emission peaks at 604 nm which was due to the 1D2→3H4 transition as the La3+ concentration increased. The results indicate that when the La3+ ion co-doped (Y0.998-yPr0.002)InGe2O7, the unit cell of lattice expands, but the partial Pr-O distance is decrease. The energy level splitting for 4f5d state increases which was due to the Pr3+ ion affected by a stronger crystal field. The larger crystal field caused the 4f5d state shifts to a lower energy state, and is closer to the 1D2 state of Pr3+ ion. High efficiency nonradiative transitions may populate the 1D2 state of Pr3+, leading the emission intensities of the 1D2→3H4 transition to increase. The optimal PL intensities is obtained when y=0.1 for (Y0.998-yLayPr0.002)InGe2O7 phosphor. When the La3+ ion is increased, which give rise the number of oxygen vacancies, but did not affect the luminescence properties of (Y0.998-yLayPr0.002)InGe2O7 phosphor. Proper amount of oxygen vacancy is commonly regarded, and dramatically promotes the energy transfer as a sensitizer resulting in an increase of PL intensities. However, when the La3+ concentration increases further, a more asymmetrical structure leads the oxygen vacancies to increase and a second phase form, excessive oxygen vacancies will be generated, then results the luminescence to quench. The CIE chomaticity coordinates of (x=0.408，y=0.330) shift to the warm white light region as the La3+ concentration increases.