新穎白光發光二極體螢光體合成與發光特性之研究

Abstract

本研究利用固態合成法製備A (Ln = Eu, Tb)、B: R3+ (R = Eu, Tb, Ce)、C: R3+ (R = Eu, Tb, Ce)、D: R3+ (R = Eu, Ce)、E: R3+ (R = Eu, Ce)及F: Eu3+等六大系列螢光體，並利用螢光光譜、漫反射光譜、X-ray粉末繞射與掃描式電子顯微鏡進行其晶體結構、表面形態與發光特性之鑑定，其主旨在於開發可供近紫外或藍光光源激發且具有新穎化學組成螢光體。 在Eu3+摻雜系列螢光體發射紅光，在不同主體中所摻雜Eu3+，其激發光譜並無太大變化，僅F: Eu3+由於含自身釩酸根活化，造成激發光譜呈寬化現象。由摻Eu3+螢光體放射光譜特性可將主體分為： Eu3+離子佔據反轉或非反轉對稱格位者，其分別由5D0→7F1磁偶極躍遷及5D0→7F2電偶極躍遷主導。在Tb3+摻雜系列螢光體發射綠光，摻雜Tb3+離子之不同螢光體螢光光譜間並無太大差異，在高Tb3+摻雜濃度時，由於Tb3+離子5D3與5D4之間的交叉弛豫，現象造成其放射光譜由5D4→7Fj的電子躍遷主導。 在Ce3+摻雜離子螢光體中，主體晶場強度決定了Ce3+離子5d軌域分裂強弱，進而影響螢光體發光波長，本研究探討了具石榴石結構的二種Ce3+摻雜D和E螢光體，D:Ce3+和E:Ce3+分別放射綠光及黃光，理論計算顯示其主體晶場分裂能D(A)分別為22,800cm-1及26,000cm-1，本研究深入探討晶場分裂能對螢光體放光波長之關係。在B:Ce3+,Tb3+和C:Ce3+,Tb3+兩螢光體中，本研究發現Ce3+→Tb3+能量轉移極可能藉由共振型偶極-偶極及偶極-四極交互作用的機制進行，此外還需考慮Tb3+離子之間的交叉弛豫。

Novel phosphors with compositions of A (Ln = Eu, Tb), B: R3+ (R = Eu, Tb, Ce), C: R3+ (R = Eu, Tb, Ce), D: R3+ (R = Eu, Ce), E: R3+ (R = Eu, Ce), and F: Eu3+ were synthesized by solid state method. Their crystal structures, luminescence properties, microstructure were characterized by photoluminescence, and diffuse reflectance spectroscopy, X-ray powder diffraction, and scanning electron microscopy. Our main research goals are to develop novel phosphors and investigate their luminescence properties of rare earth-activated phosphors for ultraviolet and blue LEDs. The excitation spectra of various Eu3+-doped red phosphors are of no difference, only F:Eu3+ shows a broad excitation spectrum owing to the presence of self-activated host. When Eu3+ occupies in inversion and non-inversion center, the emission spectrum are dominated by the magnetic dipole 5D0→7F1 transition and electric dipole 5D0→7F2 transition, respectively. Tb3+ spectrum has no difference among different hosts. At high Tb3+ concentration, the emission spectrum is dominated by 5D4→7Fj transition as a result of cross- relaxation between 5D4 and 5D3 levels. The crystal field of host influences 5d orbital splitting and results in different emission wavelengths. In this research, D:Ce3+ and E:Ce3+ were found to be green- and yellow-emitting phosphors, respectively. Calculation of the crystal field splitting energy (D(A)) illustrates the observed correlation between D(A) and emission wavelength of phosphors. The D(A) for D:Ce3+ and E:Ce3+ were found to be 22,800cm-1 and 26,000cm-1, respectively. The energy transfer between Ce3+ and Tb3+ ions in B:Ce3+,Tb3+ and C:Ce3+,Tb3+ was also studied and the energy transfer from Ce3+ to Tb3+ has been predicted to be via dipole-dipole interaction, dipole-quadrupole interaction and cross- relaxation between Tb3+ ions.