鹼土鍺酸鹽螢光體主體組成效應與發光特性之研究

Abstract

摘要 本研究以固態法合成化學式為Ca2GeO4：R ( R = Mn2+、Bi3+、Tb3+、Eu3+)與CaGeO3：R¢( R¢= Bi3+、Mn2+)兩系列鹼土鍺酸鹽螢光體，並且藉由等價數的離子取代改變Ca2GeO4與CaGeO3主體晶格組成，以探討主體組成與主體晶場環境對螢光體發光特性的影響。我們利用X光繞射儀、螢光光譜儀、螢光衰減量測系統與掃瞄式電子顯微鏡等技術進行螢光體的晶體結構及發光特性的研究。 為了深入探討主體組成變化對鍺酸鹽螢光體發光所產生的效應，本論文分別合成了並探討（Ca1-x Srx）2GeO4 : R與（Ca1-ySry）GeO3 : R¢兩系列螢光體，其X光繞射圖譜與紫外光致發光光譜分析研究顯示：主體晶格中Sr2+的取代量越多，則兩系列主體晶格會隨之增大，且(Ca1-x Srx)2GeO4：R ( R= Mn2+、Bi3+)光譜放射峰波長呈現藍位移現象。但(Ca1-x Srx )2GeO4：R ( R = Tb3+、Eu3+)中源自於f → f遷移的放射光譜則不受主體取代效應與主體晶格尺寸的影響。而另一（Ca1-ySry）GeO3 : Mn2+系列中的，為一產生橘黃色光的螢光體，當其主體晶格中Sr2+的取代量增多時，則其放射波長隨之呈現些許藍位移的現象。而CaGeO3 : Bi3+則為一產生弱藍紫光螢光體，若將主體中的Ca2+以Sr2+取代，則肉眼無法觀察其發光現象。

Abstract Two series of calcium germanate phosphors with the compositions of Ca2GeO4:R (R = Mn2+, Bi3+, Tb3+, Eu3+) and CaGeO3:R' (R' = Bi3+, Mn2+) have been prepared by solid-state reactions. Investigations on the effect of host compositions and crystal field environment on the luminescent properties of the germanate-based phosphors were attempted by systematic isovalent cation substitution. The crystal structure and luminescence of the two series of phosphors were characterized by using techniques of X-ray diffraction (XRD), photoluminescence (PL), fluorescence decay measurements and scanning electron microscope (SEM). Two series of strontium-substituted Ca2GeO4:R and CaGeO3:R' phases were also prepared and their effect of host compositions on the luminescence was investigated. With increasing substituted Sr2+ contents, the lattice dimensions for both series of phases were found to increase, whereas the emission wavelength (lem) for (Ca1-xSrx)2GeO4:R (R = Mn2+, Bi3+) phases was found to decrease (i.e., blue shift), as indicated by the XRD profile and PL spectra analyses. On the other hand, the lem's attributed to the f → f transitions of Tb3+- and Eu3+ were found to be independent of Sr2+ substitutions or lattice dimensions for R-activated (R = Tb3+ and Eu3+) (Ca1-xSrx)2GeO4 phases. On the other hand, with increasing substituting Sr2+ content the lem for orange-yellow emitting (Ca1-ySry)GeO3:Mn2+ was found to exhibit slight blue shift. CaGeO3:Bi3+ was found to exhibit weak blue-violet emission, however, SrGeO3:Bi3+ was discovered to exhibit no luminescence that can be observed by naked eyes.