新穎三價鈰與兩價銪離子活化螢光體合成與發光特性之研究

Abstract

本論文研究利用固態反應製備BaMg2Al6Si9O30:R (R =Eu2+, Ce3+)、SrMg2Al6Si9O30:R (R =Eu2+, Ce3+)、YCa3(GaO)3(BO3)4:R (R =Ce3+)與Na2CaMg(PO4)2:R (R =Eu2+, Ce3+, Eu2+/Mn2+, Ce3+/Tb3+)等四大系列螢光體，於上述主體分別摻入Ce3+或Eu2+作為活化劑分別取代各主體中Ba2+，Sr2+，Y3+與Ca2+等陽離子格位，XRD晶相分析顯示主體不因Ce3+或Eu2+之摻入而改變原晶體結構，再經漫反射光譜確認主體在Ce3+或Eu2+的激發波段並無吸收且所有光學特性來自稀土離子。此外，摻雜Ce3+與Eu2+之螢光體，發光中心之能階受主體的影響很大，光譜涉及f→d 躍遷之激發與放射呈現寬帶，並造成發光波長紅位移。

本研究第一部分探討Ce3+與Eu2+分別摻雜之螢光體BaMg2Al6Si9O30、 SrMg2Al6Si9O30、YCa3(GaO)3(BO3)4與Na2CaMg(PO4)2，在主體之共價/離子性的關鍵因素影響下，因d(Eu2+-O2-)Ba2+ > d(Eu2+-O2-)Sr2+，故BaMg2Al6Si9O30 : Eu2+放光波長較SrMg2Al6Si9O30 : Eu2+紅移,另外具有雙原子存在之主體YCa3(GaO)3(BO3)4:Ce3+則因共價性增強，使激發波長更紅移。 第二部份為以離子取代試圖改善螢光體YCa3(GaO)3(BO3)4：R (R=Ce3+)、BaMg2Al6Si9O30：R (R=Eu2+,Ce3+)放光波段過於短之缺點，(Ca2+部分取代Ba2+與Gd3+、La3+部分取代Y3+)，企圖造成離子缺陷使之放光更紅移或者增加放光強度，並且不破壞原主體之純相。

第三部份則於Na2CaMg(PO4)2活化螢光體中分別共摻雜Ce3+與Tb3+離子及Eu2+與Mn2+離子，以探討其能量轉移機制，依據Dexter多偶極交互作用的能量轉移公式，可得Eu2+/Mn2+之能量轉移為交換交互作用，而Ce3+/Tb則屬於偶極-偶極交互作用。

Novel phosphors with four series of compositions of BaMg2Al6Si9O30 : R (R=Eu2+, Ce3+), SrMg2Al6Si9O30 : R (R=Eu2+, Ce3+), YCa3(GaO)3(BO3)4 : R (R=Ce3+), and Na2CaMg(PO4)2 : R (R=Eu2+, Ce3+, Eu2+/Mn2+, Ce3+/Tb3+) phosphors were synthesized by solid state method. Each of these compounds was solely doped with Ce3+or Eu2+, which is expected to substitute for the lattice site of Ba2+, Sr2+, Y3+, Ca2+, respectively. By comparing X-ray diffraction data, the crystal structure of the hosts retained after doping of small amount of rare earth ions. Through the measurements of diffuse reflectance spectrum for both doped and un-doped samples, we found that all of the optical emissions were resulted from the doped rare earth ions. We have also analyzed the structure of the hosts and made attempts to correlate the luminescence behaviors and crystal structure. Because f → d transition involved the excited state of luminescence center is affected greatly by host, and exhibits a broad excitation spectrum. Except the covalency of the host will cause all luminescence center d-orbital excited state decrease causing red shifting, crystal field strength also plays an important role.

Firstly, with the unique features of the inherent d-f electronic transition in Ce3+ and Eu2+, Eu2+-activated BaMg2Al6Si9O30, SrMg2Al6Si9O30, respectively, YCa3(GaO)3(BO3)4, and Na2CaMg(PO4)2 phosphors with five-nine-and twelve-coordinated lattice sites. With the same crystal structure, the λem of BaMg2Al6Si9O30: Eu2+ was found to be longer than that of SrMg2Al6Si9O30: Eu2+ because of Ba(Eu2+-O2-) > Sr(Eu2+-O2-). With stronger covalence of the host YCa3(GaO)3(BO3)4 : Ce3+ the λex was found to undergo a red shifting.

The second part, for the sake of improving short emission wavelength of YCa3(GaO)3(BO3)4 phosphor and BaMg2Al6Si9O30 doped with Ce3+ and Eu2+, respectively, which causes difficulties in application. Thus, we partially replace the cation Ba2+ with Ca2+ with smaller size and substituted partial cation Y3+ with Gd3+and La3+, which resulted in ion defect emission, wavelength red shifting and emission intensity enhanced, with the crystal structure of host retained.

The third part investigates the mechanism of energy transfer between co-doped Eu2+ and Mn2+or Ce3+ and Tb3+, respectively, in Na2CaMg(PO4)2 phosphors. In accordance with Dexter electric multipole interaction energy transfer formula, the energy transfer of Eu2+/Mn2+ was found to be due to the exchange interaction, whereas that observed in Ce3+/ Tb3+ codoped Na2CaMg(PO4)2 Ce3+/Tb belong to the electric multipole interaction.