A Study on the Host Composition Effect、Energy Transfer and Luminescence for MAl2B2O7(M=Ca, Sr, Ba) Phosphors
|Keywords:||鋁硼酸鹽;螢光體;能量傳遞;主體組成效應;aluminoborate;phosphor;Energy transfer;Host Composition Effect|
|Abstract:||本論文係以固態反應合成MAl2B2O7(M = Ca, Sr, Ba)等三系列螢光體。藉由不同的發光離子之摻雜以探討主體組成、發光離子與主體之間的作用力與兩發光活化劑離子間的作用力對螢光體發光特性的影響。本論文亦利用X光繞射儀（XRD）、光致發光光譜儀（PL）、掃瞄式電子顯微鏡（SEM）與準分子雷射（excimer laser）光源針對螢光體的結構與發光的特性進行量測與分析。
本論文首先探討Eu2+離子激活的SrAl2B2O7 螢光體發光特性，並以Ca2+與Ba2+離子系統化的取代SrAl2B2O7主體晶格中Sr2+的格位，以深入瞭解主體與發光離子之間的交互作用；另一方面，本研究也探討MAl2B2O7: Pb2+,R3+(M1= Sr, Ba；R= Dy, Sm)四系列螢光體中能量傳遞的機制。
本研究發現Ca2+及Ba2+對Sr2+離子之取代所形成 (Sr1-xCax)Al2B2O7與(Sr1-xBax)Al2B2O7兩系列完全固溶液， PL光譜顯示：波峰為418 nm 的SrAl2B2O7: Eu2+離子的發射峰源於4f65d1→4f7躍遷。在系統化地改變主體結晶場強度後，本論文發現：以Ba2+取代Sr2+時，主體結晶場強度變大，而此時Eu2+的放射峰波長呈現藍位移；而當以Ca2+取代Sr2+時，結晶場強度變小，Eu2+放射峰波長呈現紅位移。
此外，本論文亦探討MAl2B2O7主體中能產生能量交換的Pb2+-Dy3+與Pb2+-Sm3+離子對。在MAl2B2O7的主體中，Pb2+發射峰值為390 nm，其半高寬約為100 nm，為一典型的3P0→1S0的躍遷；而Dy3+的發射峰值為483 nm的藍光 (4F9/2→6H15/2)與575 nm的黃光 (4F9/2→6H13/2)；Sm3+的PL發射峰值分別為564nm（4G5/2→6H5/2）、600nm（4G5/2→6H7/2）與646nm（4G5/2→6H9/2）。上述係利用Pb2+發射光譜與Dy3+及Sm3+吸收光譜重疊的現象加以詮釋上述能量傳遞之機制。
With various types of cation doping the effect of host compositions for (Sr,M)Al2B2O7:Eu2+ (M = Ca, Ba) phases and energy transfer between activator-host and activator-coactivator for MAl2B2O7:Pb2+,R3+ (M = Sr, Ba; R = Dy, Sm) phases derived from solid-state synthesis were investigated, respectively. The experimental results of luminescence characteristics and microstructures for the MAl2B2O7 phosphors were obtained based on X-ray diffraction (XRD), photoluminescence (PL) spectra, scanning electron microscope (SEM), chromaticity coordinates, and decay time measurements. The effect of host composition on the luminescence of Eu2+-activated SrAl2B2O7 phases, originated from interaction of host-activator or activator-coactivator, was investigated by systematic substitution of Ca2+ and Ba2+ for Sr2+ ion in the host lattice. Furthermore, the attempt to understand the energy transfer mechanism in MAl2B2O7:Pb2+, R3+ (M = Sr, Ba; R = Dy, Sm) phosphors was also made in this work. The formation of complete solid solutions was observed in the two series of (Sr1-xMx)Al2B2O7:Eu2+ phases with M = Ca, Ba, as indicated by XRD profile analysis. The emission attributed to 4f65d1 → 4f7 transition was found to center at 418 nm, as indicated by the PL spectra. An apparent blue (or red) shift in the emission wavelength (lem) of Eu2+ attributed to the weakening (or strengthening) of crystal field was observed when Sr2+ is replaced by Ba2+ (or Ca2+) ion. On the other hand, the energy transfer of Pb2+→Dy3+ and Pb2+→Sm3+ pairs in the host lattices of MAl2B2O7 (M = Sr, Ba) was also investigated. As indicated by PL spectra, the lem attributed to 3P0→1S0 and the FWHM (full width at half maximum) for Pb2+ were found to be 390 nm and 100 nm, respectively, whereas the lem's for Dy3+ and Sm3+ were found to be 483 nm (4F9/2 →6H15/2) and 575 nm (4F9/2→6H13/2) for the former and 564 nm (4G5/2→6H5/2), 600 nm (4G5/2→6H7/2), and 646 nm (4G5/2→6H9/2) for the latter, respectively. The mechanism for energy transfer between Pb2+ and Dy3+ or Sm3+ in the MAl2B2O7 hosts was rationalized by the empirically observed overlapping of the emission spectra for Pb2+ and the absorption spectra for Dy3+ or Sm3+. In addition, the empirical decay lifetimes found for MAl2B2O7:Pb2+,R3+ (M = Sr, Ba; R = Dy, Sm) also support the fact of energy transfer observed in Pb2+-R3+ pairs.
|Appears in Collections:||Thesis|