| Aluminate-based red phosphors have some practical applications in white LED (WLED) owing to their excellent chemical stability, heat resistance and simple preparation process. In this thesis, a series of phosphors including Sr4Al4O25: M(M=Mn4+, Cr3+), CaAl4O7:M(M=Mn4+, Cr3+, Sm3+) and CaAl2O4:M(M=Cr3+, Eu3+, Sm3+) were prepared, and their photoluminescent properties and luminescence mechanism were discussed. The main concepts are as follows.(1) Sr4Al14O25:M(M=Mn4+, Cr3+) red phosphors were prepared by solid-state method. When excited by NUV light, Sr4Al14CO25:Mn4+ phosphor exhibits a sharp emission peak at 651 nm, which can be ascribed to the 2Eâ†'4A2 transition of Mn4+ ion. It is shown that the CIE coordinate of Sr4Al14O25:Mn4 +is located at a deep red area. It is also found that co-doping of Ge4+ can effectively enhance the luminescence intensity of Sr4Al14O25:Mn4+ phosphor and the optimal concentration of Ge4+is 0.5 moL%. However, co-doping of Sm3+ reduces the luminescence intensity of this material. Subsequently, experimental results reveal that the main emission peak of Sr4Al14O25:Cr3+ is located at 690 nm, which is ascribed to the 2Eâ†'4A2 transition of Cr3+ ion. The CIE coordinate of Sr4Al4O25:Cr3+ is also located at a deep red area. The results also show that the co-doping of Sm ions into Sr4Al4O25:Cr3+ does not change the positions of excitation band & emission band and significantly improves the luminescent properties. In this thesis, a radiative-form energy transfer from Sm3+ to Cr3+ had been observed for the first time in the Cr, Sm-co-doped Sr4Al14O25 red phosphors.(2) The CaAl4O7:M(M=Mn4+, Cr3+, Sm3+) red phosphors were prepared by solid-state method. Firstly, it is found that the excitation peaks of CaAl4O7:Mn4+ at 332 nm and 460 nm are ascribed to the 4A2â†'4T1 and 4A2â†'4T2 transition of Mn4+ ion, respectively. The emission peak of CaAl4O7:Mn4+ at 652 nm is ascribed to the 2Eâ†'4A2 transition of Mn4+ and the optimal doping concentration of Mn4+is 0.05 mol.%; Moreover, co-doping of ions such as Li+, Na+ and K+ can effectively increase the luminescence intensity of CaAl4O7:Mn4+ phosphor. Secondly, it is shown that the excitation peaks of CaAl4O7:Cr3+ are located at 414 nm and 564 nm and the emission peak is located at 690 nm. The optimal doping concentration of Cr3* in CaAl4O7 is 0.2 mol.%. Finally, it is shown from the luminescence spectra of CaAl4O7:Sm3+ that the main emission peaks are located at 362 nm,375 nm and 404 nm, which are ascribed to the H6/2â†'4F7/2, 8H6/2â†'8P3/2 and H6/2â†'4L13/2 transition of Sm3+ ion, respectively. The emission peaks of CaAl4O7:Sm3+ are located at 564 nm,599 nm and 651 nm, which are ascribed to the 4G6/2â†'8H6/2,4G6/2â†'8H7/2 and 4G6/2â†'8H8/2 transition of Sm3+ ion, respectively.The optimal doping concentration of Sm3+ in CaAl4O7 is 2.0 mol.%. It is shown from chromaticity diagram that the CIE coordinates of CaAl4O7:M(M=Mn4+,Cr3+) are located at the deep red areas, whereas the CIE coordinate of CaAl4O7:Sm3+ is located at an orange red area.(3) CaAl2O4:M(M=Cr3+, Eu3+, Sm3+) were also prepared by solid-state method. It is found that the excitation spectrum of CaAl2O4:Cr3+ consists of two board peaks located at 415 nm and 564 nm, which are ascribed to the 4A2â†'4Ti and 4A2â†'4T2 transition of Cr3+ respectively. The emission peak of CaAl2O4:Cr3+at 690 nm is ascribed to the 2Eâ†'4A2 transition and the optimal doping concentration of Cr3+ in CaAl2O4 is 0.5 mol.%. The CIE coordinate of CaAl2O4 Cr3+ is located at a deep red area. Subsequently, it is found that the excitation spectrum of CaAl2O4:Sm3+ consists of three board peaks located at 361 nm,374 nm and 403 nm, respectively, which are ascribed to the 8H6/2â†'4F7/2,8H6/2â†'8P3/2,8H6/2â†'4L13/2 transition of Sm3+, respectively. Next, it is shown that the main emission peaks of CaAl2O4:Sm3+ are located at 562 nm,599 nm and 645 nm, which are ascribed to the 4G6/2â†'8H6/2,4G6/2â†'H7/2,4G6/2â†'8H8/2 transition of Sm3+, respectively. The optimal doping concentration of Sm3+ in CaAl2O4 is 2.0 mol.% and the CIE coordinate of CaAl2O4:Sm3+is located at an orange red area. In this section, the luminescence properties of CaAl4O7 Eu3+ were also investigated. It is found that the excitation spectrum of CaAl2O4:Eu3+ consists of two board bands:one is located at 200～300 nm (NUV light) which is ascribed to the charge transfer band (CTB) of O2â†'Eu3+, and the other is located at 363 nm,376 nm,383 nm,393 nm and 414 nm,which are ascribed to the 7F0â†'5D4,7F0â†'5Gj,7F0â†'5Lj,7F0â†'5L6 and 7F0â†'5Db transition of Eu3+ ion, respectively. The main emission peaks of CaAl2O4:Eu3+ is located at 574 nm (5Dâ†'7Fo),585 nm (5D0â†'7F1) and 614 nm (5Dâ†'7F2), respectively. The optimal doping concentration of Eu3+ in the CaAl2O4 is 10.0 mol%and the CIE coordinate of CaAl4O7:Eu3+ is located at a red area. |
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