新穎錫酸鹽螢光體之製備與發光特性之研究

Abstract

本研究之構想係以Cd2+或Ti4+離子，系統化地分別取代Zn2SnO4主體晶格中的Zn2+或Sn4+離子，以深入瞭解了解主體組成與晶體結構的變化，對具有尖晶石結構的Zn2SnO4螢光體中發光特性的效應；另一方面，尋找適合的的活化劑離子，來激活Ca2SnO4主體，以期能得到發白光的螢光體。 本研究發現：Cd2+或Ti4+離子對主體晶格中的Zn2+或Sn4+離子的取代，在0≦x≦1.4或0≦y≦1之範圍，均能形成(Zn2-xCdx)SnO4或Zn2(Sn1-yTiy)2O4連續性固溶液。隨著陽離子取代量的變化，主體晶格的結晶場亦隨之變化，這點在光致發光光譜中可觀察到，(Zn2-xCdx)SnO4自身活化的放射峰隨Cd2+離子取代量遞增，呈現紅位移之現象；Zn2(Sn1-yTiy)O4自身活化的放射峰隨Ti4+離子取代量遞增，呈現藍位移之現象。 以Ca2SnO4主體為主體，摻加不同的發光中心離子，可以得到發不同顏色的螢光體，本研究所嘗試的離子有：Eu3+（紅色）、Tb3+（綠色）、Ce3+（藍色）、Pr3+（橘色）與Dy3+（黃色）等稀土離子與Cr3+、Mn2+、Bi3+（青綠色）、Pb2+等金屬離子，其中只有Cr3+、Mn2+與Pb2+三離子，無法激活錫酸鈣。透過以上結果，本研究將Eu3+、Tb3+、Ce3+三種離子同時摻入錫酸鈣的主體中，透過三種活化劑濃度的調配，可以合成接近發白光的螢光體Ca1.985SnO4:0.5Ce3+,0.5Tb3+,0.5Eu3+，其CIE座標為x = 0.289、y = 0.277，已接近理想的白光（x = 0.315，y = 0.320）。

A systematic substitution of Cd2+ or Ti4+ for Zn2+ or Sn4+ in the host lattice of Zn2SnO4 was attempted to investigate the effect of host compositions and crystal structure on the luminescence of some stannate phosphors with inverse spinel-type structure. On the other hand, attempts were also extended to investigate the effect of dopant concentration for rare-earth coactivated Ca2SnO4 with Sr2PbO4-type structure as a potentially white-emitting phosphor. As indicated by X-ray diffraction profiles, two series of complete solid solutions of (Zn2-xCdx)SnO4 and Zn(Sn2-yTiy)O4 were found to form with the composition range of 0 < x < 1.4 and 0 < y < 1, respectively. The wavelength of self-activated emission (lem) for (Zn2-xCdx)SnO4 phases was found to exhibit an apparent red shift, whereas that for Zn(Sn2-yTiy)O4 was found to exhibit a blue shift. These observations can be rationalized by considering the weakening (or strengthening) of crystal field strength and the shrinkage (or expansion) of band gap for the Zn2SnO4 host lattice upon Cd2+ or Ti4+ substitution. With various doping of rare earths (i.e., Eu3+, Tb3+, Ce3+, Pr3+, Dy3+), transition metal ions (i.e., Cr3+, Mn2+), and main group ions (i.e., Bi3+, Pb2+) into the Ca2SnO4 host lattice, we have found that Ca2SnO4 could not be activated by dopants such as Cr3+, Mn2+, and Pb2+. Furthermore, in an attempt to develop white-emitting stannate-based phosphors, we have also investigated the activation and photoluminescence for Ca2SnO4 phase by systematic concentration tuning of coactivators Eu3+, Tb3+, and Ce3+. The C.I.E. chromaticity coordinates for the white-emitting Ca1.985SnO4:0.5Eu3+,0.5Tb3+,0.5Ce3+ phase under ultraviolet excitation has also been determined to be (0.289, 0.277), which was found to be close to that for the standard day light-emitting illuminant C (6500 Å), (0.315, 0.320).