利用X光能譜技術研究螢光粉末Sr2SiO4: Eu3+之電子和原子結構

The Electronic and Atomic Structures of Sr2SiO4: Eu3+ Phosphor Powder Studied by X-ray Spectroscopies

鄭世燕(Shi-Yan Zheng)

指導教授 ： 彭維鋒

淡江大學/理學院/物理學系博士班/博士(2021年)

https://doi.org/10.6846/TKU.2021.00340

摘要

採用溶膠凝膠法(Sol-gel Method)製備螢光粉末樣品Sr2SiO4: Eu3+ (SSO: xEu3+, x= 1.0, 2.0及5.0 %)，研究其晶體結構、發光機製、電子/原子結構以及能隙性質並獲得這些性能間的關聯性。
X光粉末繞射分析顯示SSO: xEu3+螢光粉末中皆含有斜方晶系結構α'-SSO與單斜晶系結構β-SSO混合相。當SSO: xEu3+螢光粉末受紫外光 (= 250 nm, ~4.96 eV)激發時，其可發出黃色 (~590 nm)、橙色 (~613 nm)及紅色 (~652 與 703 nm) 波段的可見光。這些可見光主要由 4f-4f 電子躍遷而產生，其涉及基體晶格中活化劑Eu3+的多重激發5D0 7FJ (J= 1, 2, 3及4)能級躍遷。
Sr K-edge及Eu L3-edge的X光吸收近邊結構(X-ray Absorption Near Edge Structure, XANES)/延伸X光吸收精細結構(Extended X-ray Absorption Fine Structure, EXAFS)，O K-edge XANES及K X光發射光譜(X-ray Emission Spectroscopy, XES)研究發現，樣品發光機製與 Eu3+-O2-耦合局域電子/原子結構以及基體晶格的能隙緊密相關。
由於合成的SSO: xEu3+螢光粉末的基體晶格間隙中形成類Eu2O3結構，其充當提供者(Donors)雜質，有利於電子從O 2p-Eu 4f /5d未佔據態(主要為O 2p-Eu 5d未佔據態)向第一激發態5D0發生非輻射遷移，之後再促使電子通過輻射躍遷從第一激發態5D0躍遷至基態7FJ，該電荷遷移過程是Eu3+離子摻雜濃度增加時樣品其光致發光光譜(Photoluminescence Spectroscopy, PL)強度增強的主要原因。
通過以上研究顯示，SSO: xEu3+螢光粉對於近紫外晶片而言不失為一種優良的光轉換候選螢光粉，並可廣泛應用在基於紫外發光二極體上。

關鍵字

三價銪離子摻雜於矽酸鍶螢光粉末 ； X光吸收近邊結構 ； 延伸X光吸收精細結構 ； X光發射光譜 ； 光致發光光譜 ； X光繞射 ； 一般結構分析系統

並列摘要

A series of Eu3+-activated strontium silicate phosphors, Sr2SiO4:xEu3+ (SSO:xEu3+, x= 1.0, 2.0 and 5.0 %), were synthesized by a sol-gel method, and their crystalline structures, photoluminescence (PL) behaviors, electronic/atomic structures and bandgap properties were studied. The correlation among these characteristics was further established. X-ray powder diffraction analysis revealed the formation of mixed orthorhombic α'-SSO and monoclinic β-SSO phases of the SSO:xEu3+ phosphors. When SSO:xEu3+ phosphors are excited under ultraviolet (UV) light (= 250 nm, ~4.96 eV), they emit yellow (~590 nm), orange (~613 nm) and red (~652 and 703 nm) PL bands. These PL emissions typically correspond to 4f-4f electronic transitions that involve the multiple excited 5D0 7FJ levels (J= 1, 2, 3 and 4) of Eu3+ activators in the host matrix. This mechanism of PL in the SSO:xEu3+ phosphors is strongly related to the local electronic/atomic structures of the Eu3+-O2- associations and the bandgap of the host lattice, as verified by Sr K-edge and Eu L3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure, O K-edge XANES and Kα X-ray emission spectroscopy. In the synthesis of SSO:xEu3+ phosphors, interstitial Eu2O3-like structures are observed in the host matrix that act as donors, providing electrons that are nonradiatively transferred from the O 2p-Eu 4f/5d states (mostly the O 2p-Eu 5d states) to the 5D0 levels, facilitating the recombination of electrons that have transitioned from the 5D0 level to the 7FJ level in the bandgap. This mechanism is primarily responsible for the enhancement of PL emissions in the SSO: xEu3+ phosphors. This PL-related behavior indicates that SSO: xEu3+ phosphors are good light-conversion phosphor candidates for use in near-UV chips and can be very effective in UV-based light-emitting diodes.

並列關鍵字

Trivalent Europium Doped Strontium Silicate Phosphor Powder ； XANES ； EXAFS ； XES ； PL ； XRD ； GSAS

參考文獻

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