Research On The Characteratization Of Manganese, Chromium And Europium Ions Doped Several Luminescent Materials

In the first part of this dissertation, we systematically introduced the research histories, recent research situations and future application prospects on inorganic luminescent phosphors for w-LEDs, long persistent luminescence phosphors, photostimulated long persistent luminescence materials and inorganic photochromism materials. The specific study topics of this dissertation focused on transition metal ions (such as Mn4+, Mn2+and Cr3+) doped red phosphors for w-LEDs applications, long persistent luminescence phosphors and Eu2+-doped inorganic photochromism powders. According to the worldwide survey and analyses on the current study status of ions doped inorganic functional luminescent materials, we found some existed problems:the high efficient red phosphors for w-LEDs are still lacking; the long persistent phosphors which can actually meet the practical application requirements remain scarce, and the corresponding persistent luminescence mechanism still has many doubts in some details; near infrared long persistent phosphors and photostimulated long persistent materials may pave a way for the breakthrough in solving the development bottleneck of modern biological optical imaging; the study of inorganic photochromism materials is just in the early stage. Aiming at the hotspots and confronting challenges, we have carried out massive related experiments and optimization. The main research contents and results in this dissertation are summarized as follows:(1) Mn4+-doped SrGe4O9 red phosphors were prepared via high temperature solid state reaction method. The wide excitation matches well with the blue LED chips. The narrow emission lines locate around 655 nm and the intensity is about 1.2 times higher than that of the reported Sr4Al14O25:Mn4+ phosphor. In addition, we developed a new Mn4+-doped Li2MgTiO4 host red phosphor. The raw materials for this phosphor are cheap and abundant. The steady and transient state spectroscopic properties were studied systematically at high, low and room temperatures. The broad excitation is in good agreement with the blue LED chips. The emission centers at 676 nm and the emission intensity is at least quadruple higher than that of commercial phosphor 3.5MgO�0.5MgF2-GeO2:Mn4+. We found that the color rendering index (from 59.65 to 71.43) and correlated color temperature (from 6989 to 5568 K) of the obtained white light were evidently improved when fabricatd a w-LED device through coating the Li2MgTiO4:Mn4+ and commercial YAG phosphors on a blue LED chip. Moreover, based on the previous research results, we summarized the regular characteristics and proposed an empirical formula E(2Eg)=15663.33?1-278.76 on the basis of the relationship between 2Eg level energy and ?1, which can guide and verify the future research to a certain extent.(2) Mn2+-doped A2BGeO4 (A=Li, Na; B=Zn, Mg) structure materials with blue and green persistent luminescence were prepared by high temperature solid state reaction method. Mn2+-doped Li2MgGeO4 shows green persistent luminescence with duration more than 5 h; non-and Mn2+-doped Na2ZnGeO4 long persistent materials show blue and green persistent luminescence, which can last about 40 min and 4 h, respectively; non-and Mn2+-doped Li2ZnGeO4 materials show blue and green long persistent luminescence, and the corresponding duration were experimentally determined to be 5 h and 8 h, respectively. According to the investigations on their fluorescence properties, persistent luminescence decay and thermoluminescence characteristics, we confirmed the energy transfer from host to Mn2+ ions. Meanwhile, the intrinsic traps in the host were discussed and the persistent luminescence mechanism was illustrated in detail based on a constructed model.(3) Cr3+-doped Mg4Ga8Ge2O20 host materials with multifunctional properties were prepared successfully via high temperature solid state reaction method. The crystal structure was analysized using Rietveld structure refinement method. The steady and transient state spectroscopic properties were studied systematically at high, low and room temperatures, and the corresponding explanation were given. The obtained materials show near infrared long persistent luminescence with duration more than 25 h, which enables it to be used for in vivo imaging. Moreover, it shows photostimulated near infrared long persistent luminescence which can be not only induced by near infrared light but also visible light. The photostimulated near infrared long persistent luminescence can repeat for several times. Besides, this material shows photochromism that the surface color changes reversibly between white/pale green and ronbrown by alternating the UV and visible/heating stimuli. The photochromism has excellent endurance, fatigue resistance and higher temperature stability. ESR was used to confirm the reversible transitions between Cr3+ and Cr5+ accompanied with the electron trapping and releasing in reversible photochromism processes. The aforementioned three properties have some inner connections.and have confirmed to be closely related to traps. The traps distribution and trap depths in the host were revealed through thermoluminescence measurements under different conditions (such as changing the excitation wavelengths, excitation duration, excitation temperature, the waiting time after the excitation, the treating temperature after the excitation, bleaching wavelengths, and etc.) We proposed a schematic diagram and illustrated the essential mechanism behind the multifunctional properties.(4) Eu2+-doped Zn2GeO4 and Sr3YNa(PO4)3F powders were synthesized. By alternating the UV and visible/heating stimuli, the surface color of non-and Eu2+-doped Zn2GeO4 changes reversibly between white and grey. The doping of Eu2+ promotes the photochromism performance. Eu2+-doped Sr3YNa(PO4)3F material shows photochromism that the surface color changes reversibly between colorless and cyan by alternating the UV and visible/heating stimuli. The photochromism appears good endurance, fatigue resistance and higher temperature stability. We studied the traps in inorganic photochromism powders for the first time and well explained the role of traps in photochromism. Furthermore, we used ESR method, combined with the thermo luminescence results, to powerfully confirm the speculation that Eu2+can be transformed into Eu3+ under UV excitation, and the excited electrons can be captured by intrinsic defect oxygen vacancies forming color center, leading to photochromism phenomenon. Electrons can escape automatically at room temperature or passively under external stimuli (such visible light or heating treatment), and then return to Eu3+, realizing bleaching. We proposed a photochromism mechanism which can well illustrate the observed phenomenon.