本研究以鎢酸鹽類之BaLa2WO7為主體晶格材料，並以三價稀土金屬離子Eu3+、Dy3+、Sm3+、Er3+、Ho3+、Tb3+與Tm3+等摻雜於主體晶格中取代La3+位置作為活化劑，同時討論其材料合成與發光特性。同時又以Sr2+與Ca2+取代晶格中Ba2+位置，造成一晶格畸變，觀察對整體性質造成之影響。
由實驗結果顯示，以固態反應法配合高能震動球磨所製備之BaLa2WO7: Ln3+(Ln3+ = Eu3+、Dy3+、Sm3+、Er3+、Ho3+、Tb3+、Tm3+)螢光粉，在900 ~ 1350°C之煆燒溫度下可形成穩定之BaLa2WO7單斜晶單一相，而所摻雜之稀土離子可和晶格中之La3+相互取代形成固溶體，並且對表面形態不會產生太大影響，系統仍可維持一定的穩定性。
BaLa2WO7: Ln3+螢光粉體展現出強烈的W6+-O2-間電荷轉移吸收帶，而由於Ln3+-O2-之共價性太低，導致其CTS(charge transfer state)無法有效轉移給稀土離子發光，因此主要是由W6+-O2-之電荷轉移帶與稀土離子之4f內層軌域躍遷進行發光。在以Eu3+為活化劑發光中心時，產生的放光可由Eu3+離子濃度控制。在低濃度時較高能階之藍、綠光放光較強，隨摻雜量提高，5D0 → 7FJ (J=0, 1, 2)紅光放光將成為主要放光，因此其色度座標可由Eu3+摻雜濃度而改變，在適當之摻雜濃度下，BaLa2WO7: Eu3+可產生單一發光中心之白光。經由(5D0 → 7F2) / (5D0 → 7F1)非對稱指數可發現，Eu3+離子於主體晶格中佔據非對稱中心，而隨摻雜量增加，非對稱指數會持續上升直至晶格扭曲變形而產生相轉換。BaLa2WO7: Dy3+則可產生明顯之4F9/2 → 6H13/2與4F9/2 → 6H15/2之黃光與藍光放光，由於強度接近，因此其產生之光色相當接近於白光，且放光強度比例不因Dy3+摻雜量而有所改變。而經由發射光譜與衰減曲線分析，可發現Sm3+離子之4G5/2能階、Er 3+離子之4S3/2能階、Tm 3+離子之1D2能階與Ho 3+離子之5S2能階皆能產生強烈放光，且易受濃度淬滅效應影響，在低濃度下便會發生交叉緩解而使放光強度降低，同時其發光之衰減曲線亦因交叉緩解現象而產生改變，使衰減曲線呈非自然指數之衰減行為。
當以Sr2+與Ca2+取代晶格中Ba2+位置調整結構時，可發現Sr2+與Ba2+之間由於性質接近，可產生較大的固溶量而不造成結構改變。當Sr2+取代Ba2+進入晶格中，整體晶格產生變形，發光中心間之能量轉換效率增加，使放光強度因此而增強，但不改變原本放光性質，經由比對Eu3+離子(5D0 → 7F2) / (5D0 → 7F1)與Dy3+離子(4F9/2 → 6H13/2)/(4F9/2 → 6H15/2)在摻雜Sr2+之比值，可發光Sr2+並不會改變發光中心之周圍晶格環境。而Ca2+與Ba2+間之離子半徑差異較大，導致Ca2+取代時造成較大之變形，因此固溶量較低，且過大的變形降低了結晶性，雖可調整發光中心周圍對稱性，進而改變放光比例，但亦會造成整體發光強度下降。
本研究所製備之螢光粉具備各種色系，包括紅色：Sm3+與Eu3+、綠色：Er3+與Ho3+、藍色：Tm3+、近白色：Dy3+，最佳激發波長皆位於350 ~ 450 nm之間，在近紫外光與藍光區均能應用，顯示其具有發展成為白光LED照明系統之螢光粉的應用潛力。

In this work, BaLa2WO7: Ln3+(Ln3+ = Eu3+, Dy3+, Sm3+, Er3+, Ho3+, Tb3+, Tm3+) phosphors have been synthesized via a solid-state reaction. The absorption, excitation, emission and decay curves were obtained to study the luminescence properties. The effects of substituting Ba2+ with Sr2+ and Ca2+ in BaLa2WO7: Ln3+ to improve the optical properties are also studied.
The experimental results indicated that the crystal can be assigned to the structural nature of the BaLa2WO7 single phase as the calcination temperature in the range of 900 ~ 1350°C, and the rare-earth ions were satisfactorily substituted for the La3+ ions in BaLa2WO7 monoclinic structure. BaLa2WO7 doped with rare-earth ions at different doping concentrations do not significantly affect morphology.
The broad band located around 338 nm of the excitation spectrum is due to the charge-transfer state (CTS) band caused by electron transfer from oxygen to tungsten (ligand-to-metal charge-transfer transitions, LMCT). However, the CTS band of the oxygen 2p orbital to the empty 4f orbital of Ln3+ is weak and immersed in the CTS band of WO6 due to their week covalency. The sharp peaks in the range of 350 to 600 nm are assigned to the typical intra-4f forbidden transitions of the Ln3+ ions. The emission spectra of Eu3+-doped BaLa2WO7 phosphors excited at 395 nm exhibit a series of sharp peaks, which are attributed to the 5D0 → 7FJ (J=0,1,2,3,4) transitions. Luminescence from higher excited states, such as 5D1, 5D2, and 5D3, were also observed at low Eu3+ concentration. The optimal emission intensity of 5D0 → 7F2 red emission is at x=0.4 (BaLa1.6Eu0.4WO7). The chromaticity coordinates of Eu3+-doped BaLa2WO7 phosphors vary with Eu3+ content from white, orange-red, to red. The (5D0 → 7F2) / (5D0 → 7F1) asymmetry ratio increased with increasing Eu3+ concentration, reveling that the local structural symmetry around Eu3+ significantly changed as Eu3+ became incorporated into BaLa2WO7. Dy3+-doped BaLa2WO7 phosphors emit bright near-white light. Under an excitation wavelength of 351 nm, two dominant emission peaks were seen at 485 and 572 nm, which correspond to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+, respectively. The intensity of the emission from the 4F9/2 → 6H15/2 transition was higher than that from the 4F9/2 → 6H13/2 transition, revealing that Dy3+ occupied a relatively symmetrical site in BaLa2WO7: Dy3+. The doping of Dy3+ ions did not change the site symmetry even at a high concentration.
By analyzing the emission spectra and decay behaviors, the energy transfer due to cross-relaxation and concentration quench effect over ion-ion interaction between two neighboring rare-earth ions provide an extra decay channel, the luminescence centers have different local environments and the existence of more than one relaxation process. When excitation energy from an ion decaying from a highly excited state promotes a nearby ion from the ground state to the metastable level, cross-relaxation can occur easily between two neighboring rare-earth ions, such as Sm3+(4G5/2), Er3+(4S3/2), Tm3+ (1D2), and Ho3+(5S2).
Introducing Sr2+ into Ba2+ site can further enhance the emission intensity but do not change the site symmetry around rare-earth ions. However, the substitution of Ba2+ by Ca2+ leads to an intense crystal distortion, resulting in a degradation of the local site symmetry around Eu3+ and Dy3+. Consequently, the color of Ca-substituted phosphors, Ba1-yCayLa2WO7: Dy3+, can be tuned by increasing Ca2+ content.
All synthesized phosphors in the study can emit different colors by doping different kinds of activators and varying doping concentrations, such as white to red (Eu3+), green (Er3+, Ho3+), orange-red (Sm3+), blue (Tm3+), and near-white (Dy3+). The experimental results revel that the excitation wavelength of BaLa2WO7: Ln3+ phosphors and the emission wavelength of blue- and UV-LEDs (350 ~ 450 nm) have closely overlapped, and the sharp emission peaks show that BaLa2WO7 is suitable for rare-earth-doped phosphors, making it an attractive candidate for use in optical applications.

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