微米級鍺酸鹽與奈米級鎵酸鹽螢光體之製備與發光特性之研究

Abstract

Zn2GeO4:Mn2+系列螢光體，在交流薄膜電激發光元件、場發射與電漿平面顯示器被認為極具應用潛力，而奈米ZnGa2O4: Mn2+螢光體在高解析顯示元件亦被認為具有提升解析度的特性。本研究分別利用固態法與熱溶劑法合成微米級Zn2GeO4:xMn2+ (x = 0.1-6.0%)及Zn2(Ge1-ySiy)O4:1%Mn2+ (0 < y <1)兩系列螢光體與奈米級ZnGa2O4:xMn2+螢光體，並深入探討其化學組成、自身活化發光與Mn2+發光特性、瞬態衰減與微米級螢光體微結構之相互關係。 在Zn2GeO4:xMn2+系列螢光體中，隨Mn2+摻雜量增加，Zn2GeO4:xMn2+的螢光衰減期變短，此可能與高含量Mn2+摻雜的樣品中Mn2+-Mn2+對形成有關；另一方面，其光致發光(PL)光譜中Mn2+放射峰波長由527 nm偏移至534 nm，呈現紅位移。瞬態衰減量測結果顯示：自身活化發光與Mn2+發光分別在奈秒與微秒時間範圍。 本研究亦探討Si的摻雜對Zn2(Ge1-ySiy)O4:1%Mn2+螢光體的發光特性、螢光衰減期與表面微結構分析之效應。研究結果發現：隨Mn2+摻雜量增加，Zn2GeO4:xMn2+的螢光衰減期變短，且其光致發光(PL)光譜Mn2+放射峰波長呈現紅位移；而隨Si的取代量增加，Zn2(Ge1-xSix)O4:xMn2+的螢光衰減期無顯著改變，但其PL光譜Mn2+放射峰波長則呈現藍位移。 最後本論文亦探討以高壓熱溶劑法，於180-220℃所合成奈ZnGa2O4:xMn2+之合成化學、發光特性與發光機制，並藉製程條件調變，以探討其與奈米螢光體發光特性與微結構的關係。以乙二胺、甲醇或甲醇/乙二胺為溶劑，均可成功合成奈米ZnGa2O4:xMn2+，當以甲醇/乙二胺為溶劑時，可明顯看出相對於塊材，其PL光譜呈現藍位移現象，此可能與其材料尺寸有密切關係。

This research is attempted to investigate the synthesis and luminescent properties of phosphors with compositions of (a) Zn2GeO4:xMn2+ (x = 0.1-6.0%), (b) Zn2(Ge1-ySiy)O4:1%Mn2+ (0 < y <1) and (c) ZnGa2O4:Mn2+ nanophosphor that have been proposed to show potential applications in field emission displays, plasma display panels and, potentially, for high resolution displays. We have investigated the synthesis, luminescence and time-resolved decay spectra for Zn2GeO4:xMn phosphors doped with different contents of Mn2+ as an activator. The microstructure of Zn2GeO4:xMn samples is highly dependent of synthetic conditions. The observed red shift in □em with increasing Mn2+ content from 527 to 534 nm has been investigated and rationalized by the presence of a weak crystal field due to the substitution of Zn2+ by Mn2+, which leads to a distorted tetrahedral lattice site. The CIE chromaticity coordinates were found to shift slightly with variation of doped Mn2+ content. The time-resolved fluorescence decay of Zn2GeO4:xMn has also been investigated. Interestingly, the shortening of fluorescence decay lifetime with increasing Mn2+ dopant concentration has been rationalized by the alteration of transition probability as a consequence of magnetic interaction between Mn2+-Mn2+ pairs in the host lattice. The effect of Si-substitution on the luminescence properties as well as the microstructures of Zn2(Ge1-ySiy)O4:xMn2+ (0 < y <1) has also been investigated. The emission of Mn2+ attributed to 4T1→ 6A1 transition was found to exhibit blue shift with increasing doped Si content, which is presumably related with the systematic broadening of gap energy of the Zn2(Ge1-ySiy)O4 host. We have also investigated the luminescence of the ZnGa2O4:Mn2+ nanophosphors synthesized by a solvothermal route by reacting composing metal nitrates in solutions of methanol, ethylenediamine or a mixture of the two at 180- 220℃. As indicated by TEM and SEM micrographs, the microstructure of nano-ZnGa2O4:Mn2+ was found to be highly dependent of the solvents used. The photoluminescence spectra of nano-ZnGa2O4:Mn2+ synthesized in solvent of methanol/ ethylenediamine were observed to exhibit a blue shift relative to those of bulk samples.