本研究以鍺酸鹽類之LaAlGe2O7作為螢光體主體晶格材料，分別將三價稀土金屬離子Ce3+, Pr3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Er3+與Tm3+等作為活化劑，摻雜於主體晶格中，討論其材料合成及光致發光特性。本研究可分為兩大部分：第一部份著重於摻雜單一稀土金屬離子於主體晶格中，討論各個活化劑的螢光特性。第二部份則藉由Gd3+與Tb3+離子的共同摻雜，討論稀土金屬離子間的能量轉移對螢光性質的影響。
由實驗結果顯示，以高能震動球磨法所製備之LaAlGe2O7: Ln3+ (Ln = 稀土金屬離子)螢光粉，在1100 ~ 1250℃煆燒可得穩定之LaAlGe2O7單一相結晶；且所摻雜的稀土離子皆可與LaAlGe2O7晶格中La3+離子相互取代形成完全的固溶體，晶體之表面型態並無太大的改變，系統仍維持一定的穩定性。
由Eu3+離子(5D07F1/5D07F2)與Dy3+離子(4F9/2→6H15/2/4F9/2→6H13/2)在LaAlGe2O7中螢光強度的比值可以得知稀土離子應填入具備中心對稱的晶格點位置。經發射光譜與衰減曲線的分析可以發現Tb3+離子之5D3能階、Pr3+離子之1D2能階與3P0能階、Tm3+離子之1D2能階、Er3+離子之4S3/2能階、Sm3+離子之4G5/2能階及，Dy3+離子之4F9/2能階，皆會隨著摻雜濃度的增加產生交叉緩解效應，使得濃度淬滅現象發生濃度明顯較低，同時發光的衰減速率亦因交叉緩解現象而產生改變，使得衰減曲線呈現非自然指數之衰減行為。由LaAlGe2O7: Ln3+ (Ln = Ce, Pr, Tb)螢光粉體的吸收及激發光譜得知，Ce3+, Pr3+及Tb3+離子的4f-4f5d躍遷吸收與LaAlGe2O7的主體晶格吸收能帶重疊，導致光游離或補償效應的產生，造成發光效應的猝滅。LaAlGe2O7: Ln3+ (Ln = Eu, Sm, Dy)螢光粉體的電荷轉移吸收帶由於Ln3+-O2-共價性過低或主體晶格吸收而導致CTS(charge transfer state)無法有效轉移給稀土離子發光，因此只能由稀土離子之4f內層軌域躍遷進行激發。
在不同稀土離子間的能量轉移研究方面，LaAlGe2O7: Gd3+, Tb3+中的Gd3+離子以兩種能量轉移機制轉移至Tb3+離子：(1)多聲子緩解與(2)交叉緩解能量轉移，不同的轉移機制會改變Tb3+離子能階的衰減速率，因而改變Tb3+離子的衰減行為。
本研究所製備的螢光粉體具備各種色系，包括藍色：Tm3+、綠色：Tb3+, Er3+, Pr3+、紅色：Eu3+, Sm3+、藍白色：Dy3+以及在紫外光區的Gd3+，最佳激發波長位於350 ~ 450 nm之間，具有發展為白光LED照明系統之螢光粉應用的潛力。

The synthesis and photoluminescent properties of lanthanum aluminum germinate (LaAlGe2O7) doped with various rare earth ions (Ce3+, Pr3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Er3+ and Tm3+) have been investigated. This study could be divided into two parts: (1) the luminescent properties of a series of rare earth ions, (2) the energy transfer properties over ion-ion interaction by codoped Gd3+ and Tb3+ ions.
The experimental results demonstrated that the crystal can be assigned to the structural nature of the LaAlGe2O7 phase as the calcination temperature in the range of 1100 ~ 1250℃, and the rare earth ions were satisfactorily substituted for the La3+ ions in the lattice. The LaAlGe2O7 powders doped with rare-earth ions at different concentrations do not significantly affect morphology.
The (5D0→7F1)/(5D0→7F2) emission ratio of Eu3+ and the (4F9/2→6H15/2)/( 4F9/2→6H13/2) emission ratio of Dy3+ reveal that the local symmetry of the activator ions belongs to inversion symmetry in the LaAlGe2O7 host lattice. By analyzing the emission spectra and decay curves, the energy transfer (cross-relaxation) over ion-ion interaction between two neighboring rare earth ions provide an extra decay channel which changes the decay curves, such as Tb3+(5D3), Pr3+(1D2 and 3P0), Tm3+(1D2), Er3+(4S3/2), Sm3+(4G5/2) and Dy3+(4F9/2). The absence of 4f-5d luminescence in LaAlGe2O7: Ln3+ (Ln = Ce, Pr, Tb) have been ascribed to quenching by photoionization or offset, which implies that the lowest 5d level of Ln3+ lies in the conduction band of the host crystal. It is recognized that no efficient charge transfer state (CTS) band occurs in LaAlGe2O7: Ln3+ (Ln = Eu, Sm, Dy) may be due to the CTS band overlaps with the absorption band of the host or the weak covalency between Ln3+ and O2−.
There were two kinds of efficient Gd3+ to Tb3+ energy transfer processes in terms of Tb3+ concentration: (1) multi-phonon relaxation, (2) cross-relaxation. When the Gd3+ to Tb3+ energy transfer includes the slow multi-phonon relaxation rate, a “grow-in” behavior of the decay curves could be observed. For high concentration Tb3+ doped samples, the fast cross-relaxation process is dominant, while only a simple exponential decay could be observed.
All synthesized phosphors in this study could emit different colors by doping different kinds of activators, such as blue (Tm3+), green (Tb3+, Er3+, Pr3+), red (Eu3+, Sm3+), bluish white (Dy3+) and ultraviolet (Gd3+). One of the interesting results of this work is that the excitation wavelengths of the phosphors and the emission wavelengths of the LED (350 ~ 450 nm) have closely overlapped, which provides the potential as the LED converted phosphors in solid state lighting technology.

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