A Study on the Synthesis and Luminescent Properties of Novel Phosphors for White-Light LEDs
|摘要:||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。
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.