The Research For Pr～(3+), Mn～(2+) Co-doped Oxide-based Quautum Cutters And The Dynamics Of The Afterglow Luminescence In Blue Long-lasting Phosphor: Sr₂MgSi₂O₇: Eu～(2+), Dy～(3+)

This dissertation included two parts. In the first part, we dealt with quantum cutting process in Pr³⁺, Mn²⁺ co-doped SrAl₁₂O₁₉, SrB₄O₇ and LaMgB₅O₁₀ systems. Main study was focused on the energy transfer process in LaMgB₅O₁₀: Pr³⁺,Mn²⁺. In the second part, the spectra and afterglow properties of long afterglow phosphor Sr₂MgSi₂O₇:Eu²⁺and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were investigated. Emphasis was made on the analyses of the roles of Eu²⁺ and Dy³⁺ in Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺.In part one, firstly, we reviewed the present research states and remain problems in visible quantum cutting phosphors. In view of the fact that almost all the known quantum cutters with high efficiency are fluorides, like LiGdF4:Eu³⁺,LiGdF4:Er³⁺,Tb³⁺.While the practical phosphors are oxides, we decided to search for oxide based visible quantum cutters, and select "Pr³⁺Mn²⁺" as the prospective activaters.In chapter three, the low temperature spectra properties of Pr³⁺ doped SrA₁₂O₁₉, SrB₄O₇, LaB₃O₆ and LaMgB₅O₁₀ were investigated by synchrotron radiation VUV light. Under VUV excitation, photon cascade emission was found in these phosphors. From the excitation spectra study, we conculded that the excitation energy can be efficiently absorbed by Pr³⁺-4f5d levels directly, but the host absorption wasn't very efficient. In the excitation spectra of SrA₁₂O₁₉:Pr³⁺, LaB₃O₆:Pr³⁺ and LaMgB₅O₁₀:Pr³⁺, along with the 4f5d absorption bands, a weak peak due to ³H₄→¹S₀ transition also was detected. From the position of ³H₄→¹S₀ transition and the absorption edge of 4f5d band, the position of Pr³⁺-¹S₀ state was determined at 2052 cm^-1, 1815 cm^-1 and 1348 cm^-1 below the lowest 4f5d state, respectively.In the following chapter, the spectra properties of Mn²⁺ doped SrAl₁₂O₁₉, SrB₄O₇, LaB₃O₆ and LaMgB₅O₁₀ were studied. In LaB₃O₆ matrix, due to the difficulty to substitute La³⁺ or B³⁺ by Mn²⁺, No emission from Mn²⁺ was found. Yet the other three phosphors showed efficient Mn²⁺ emission. In SrAl₁₂O₁₉: Mn²⁺ and SrB₄O₇: Mn²⁺, because Mn²⁺ substituted the Sr²⁺ with large ion radii which results in a weak crystal field, Mn²⁺ green emission (about 515 nm) was detected. While the emission of LaMgB₅O₁₀: Mn²⁺ was red, owing to the fact that the small ion radii site of Mg²⁺ was replaced by Mn²⁺. In the excitation spectra of SrAl₁₂O₁₉:Mn²⁺, SrB₄O₇:Mn²⁺ and LaMgB₅O₁₀: Mn²⁺, the peaks in the range of 300-550 nm were assigned to the transition of Mn²⁺-3d⁵→3d⁵, and the two bands in VUV range were attributed to host absorption and the absorption of "Mn²⁺-O^2- charge transfer states, respectively.Chapter five dealt with the Pr³⁺→Mn²⁺ energy transfer in Pr³⁺, Mn²⁺ co-doped SrAl₁₂O₁₉, SrB₄O₇ and LaMgB₅O₁₀. There wasn't any spectra overlap between the emission spectra of SrAl₁₂O₁₉:Pr³⁺ and excitation spectra of SrAl₁₂O₁₉:Mn²⁺. So, energy transfer didn't occur in SrAl₁₂O₁₉:Pr³⁺,Mn²⁺. While in the excitation spectra of SrB₄O₇:Mn²⁺ and LaMgB₅O₁₀:Mn²⁺, the ⁶A_1g→⁴E_g-⁴A_1g excitation band of Mn²⁺ had considerable spectra overlap with the Pr³⁺-¹S₀→¹I₆ emission in SrB₄O₇:Pr³⁺ and LaMgB₅O₁₀:Pr³⁺, which was favorable for energy transfer from Pr³⁺ to Mn²⁺ in Pr³⁺,Mn²⁺ co-doped sample. Such energy transfer was confirmed in SrB₄O₇: Pr³⁺,Mn²⁺ and LaMgB₅O₁₀:Pr³⁺,Mn²⁺, from the emission and excitation spectra study of the co-doped samples as well as comparing the decay curves of ¹S₀→¹I₆ transition of Pr³⁺ between Pr³⁺ singly doped and Pr³⁺,Mn²⁺ co-doped sample. The energy transfer processes converted the violet or UV emissions of Pr³⁺ into green or red emission of Mn²⁺, improved the ratio of visible emission in quantum cutting process.The Pr³⁺→Mn²⁺ energy transfer type and pathway were investigated in LaMgB₅O₁₀:Pr³⁺,Mn²⁺. The analyses showed that the energy transfer pathway was of resonant energy transfer. The critical distance of resonant energy transfer in LaMgB₅O₁₀:Pr³⁺,Mn²⁺ was calculated. As for electric dipole-dipole interaction and dipole-quadrupole interaction, the critical distance R_C was 4.78 (A|°) and 9.46(A|°), respectively. For exchanged interaction, the critical distance also was several angstroms. All the values were less than the mean distance between Pr³⁺ and Mn²⁺ in the highest concentration doped sample (R_Pr-Mn～17 (A|°)), considering a random distribution of Pr³⁺ and Mn²⁺ in LaMgB₅O₁₀ matrix. Because the ion radii of Pr³⁺ and Mn²⁺ was lager and less than the ion radii of the cations in host matrix replaced by them, respectively. The replacement would lead to the formation of some near neighboring Pr-Mn clusters in the LaMgB₅O₁₀ host to reduce the system energy. And the short distance (less than R_C) between Pr³⁺ and Mn²⁺ can account for the occurrence of Pr³⁺→Mn²⁺ energy transfer in LaMgB₅O₁₀:Pr³⁺,Mn²⁺.In part two, the spectra and afterglow properties of long afterglow phosphors Sr₂MgSi₂O₇:Eu²⁺ and Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were investigated. The results showed that the afterglow luminescence of the two phosphors originates from the 465nm blue emission of Eu²⁺-4f⁶5d→4f⁷ allowed transition. The afterglow properties of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ were better than that of Sr₂MgSi₂O₇:Eu²⁺, by the detection of afterglow spectra and the afterglow decay curves. The fitting results of the thermoluminescence curves of the two phosphors showed that, the defect levels arose from Dy³⁺ in Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ had appropriate depth and high concentration, which resulted in the longer afterglow time in Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ than that in Sr₂MgSi₂O₇:Eu²⁺.In the emission spectra of Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ excited by VUV light, the Dy³⁺ emissions were detected along with the emission of Eu²⁺. Considering the long afterglow properties of Sr₂MgSi₂O₇:Eu²⁺, we can draw the conclusion that Eu²⁺ and Dy³⁺ both have duple roles, acting as not only the luminescence centers, but also trap centers. By analyzing the dynamics of the afterglow luminescence in Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺, it was found that the Dy³⁺ acts as electron traps rather than hole traps which is accepted by many researchers, while the Eu²⁺ plays the role of hole traps.