Exploration,preparation And Luminescence Properties Of Novel Manganese Ions Doped Red Luminescent Materials

White light emitting diodes(WLEDs),as green light sources of the 21st century,have many advantages over the conventional incandescent lamp,fluorescent lamp and high-pressure gas lamp,such as high-efficiency,green initiative,long lifetime and unbreakable etc,and for these,they have a broad application for instance in illumination,automobiles,communications,medicine,military,agriculture and other fields.Currently,the mainstream technology for WLEDs is to combine a single LED chip with one or more conversion phosphors,namely,phosphor converted white light emitting diodes(pc-WLEDs).The most popular approach is the conjunction of a blue LED chip with the YAG:Ce3+ yellow phosphors because of their simple packaging processes,mature technologies and low costs.However,this design suffers from higher color teirperature(CCT>4000K)and lower color rendering index(CRI<80),which is mainly because of the low spectral power distribution in the red spectral region.The most popular solution is to supplement a high efficient red phosphor into the system especially with strong blue absorption.However,the existing red phosphors cannot satisfy the all usage requirements simultaneously.Searching for new red phosphors which can meet all requirements is the key to the development of WLEDs.In order to solve this problem,this thesis puts forward to explore,prepare and study novel manganses ions activated oxide red luminescent materials with high efficient luminescence,mild preparation conditions and eco-friendly.The main research contents and research results are as follows:(1)Take conpound K2Ge4O9 as an exanple,we first propose to use crystal field calculation on basis of exchange charge model to predict the energy levels of Mn4+ ion in crystals.The calculation shows the red emission peaking at 663 nm and the blue absorption of 4A2g(4F)?4T2g(4F)in 450-470 nm,which matches better to blue chips than commercial phosphor 3.5MgO·0.5MgF2·GeO2:Mn4+.K2Ge4O9:Mn4+ synthesized by high temperature solid state reaction method shows typical luminescence of Mn4+ and consists with the prediction.Comparison between theoretical and experimental results implies that no obvious preference of Mn4+ substitution over two different types of octahedral germanium sites Gel and Ge2.(2)Novel solid solution red phosphors(Rb,K)2Ge4O9:Mn4+ were prepared through high temperature solid state reaction method,and optimized the synthesis conditions to enhance the Mn4+ luminescence.Red luminescence of Rb2Ge4O9:Mn4+ lies in the spectral range of 620 to 720 nm,with strong absorption between 220 to 520 nm and a relatively short lifetime of the excited state of only a few hundreds of ?s.Substitution of Rb+ by the lower polarizability of the K+ ion enables tuning of the absorption cross section and of the band structure,hence,of the emission lifetime,of the excitation band shape,and of emission quantum yield.Partial substitution was also found to reduce thermal quenching of the Mn4+-related emission.(3)Efficient red phosphor LiNaGe4O9:Mn4+ was prepared by high temperature solid state reaction method.The quantum yield can reach up to 78%upon ultraviolet excitation after systematic optimization in synthesis temperature,dopant concentration of Mn4+ and sintering time.Crystal structural analysis reveals that the high efficiency Mn4+ exhibits in the compound is mainly due to the well separation of GeO6 groups from each other by GeO4 tetrahedrons in the neighborhood and therefore avoid perturbation from each other.Warm perception WLED with a color temperature of 3353K was achieved when combination of the red phosphors with a blue LED chip and YAG:Ce3+ yellow phosphors.(4)For the problem of the lower luminescent thermal quenching temperature of Mn4+doped oxide red phosphors,the red phosphor SrAl12O19:Mn4+ was selected as the research object to examine its temperature dependent luminescent properties,monitoring from 8K to 500K.Experiment results show that the phosphor suffers from obvious thermal quenching with well-founded mechanisms.Comparisons to other Mn4+ doped aluminate compounds,a general law was summarized to explore new Mn4+ doped red phosphors with better performances of luminescent thermal stability.Based on crystal field calculations using the exchange charge model,we determine the energy levels of three types of Mn4+ site in SrAl12O19 crystal structure and try to analysis the Mn4+ ions preferential occupation combined with chemical bond covalence.(5)Novel red phosphor Sr3Al10SiO20:Mn4+ was synthesized through high temperature solid state reaction method.The phosphor shows much strong and broad absorption in blue band and the intensity can comparable its UV band,thus,it can be efficiently excited by both the UV and blue light.With the increasing of excitation wavelengths,the emission peak red shifts from 661 to 663 nm,full width at half maximum(FWHM)decreases from 34 to 22 nm and fluorescence lifetime reduces.And the relative intensities of blue excitation band firstly increase and then decrease with the increasing of Mn4+ concentration.These variations may be attribute to the existence of Si which affected local crystal field environment around Mn4+.At last,temperature-dependent luminescence and Mn4+ energy levels of Sr3Al10SiO20:Mn4?were also analyzed.(6)In the initial exploration process of Mn4+ doped glass-ceramic,a new red to near infrared persistent luminescence from Mn2+ doped germanate glasses and glass-ceramics were discovered which covers the 600 to 800 nm,The octahedral Mn2+ persistent luminescence correlates tightly to the electron filled defects with depths of 0.71eV,0.80eV and 1.06eV,respectively,which can be detrapped thermally at room temperature.The detrapping can persist longer than 40 hours.Albite Na(Al,Ga)Ge3O8 which comprises sodium octahedral sites was successfully formed in glass through controlled crystallization.The controlled crystallization can lead to the precipitated crystal Na(Al,Ga)Ge3O8 with a size smaller than 50 nm and the persistent luminescence of Mn2+ ions still exists,this emanates from the incorporation of some Mn2+ on octahedral sodium sites with a more ionic bonding character in the compound.The persistence of Mn2+ red luminescence can be preserved and improved even longer than 100h through controlled the modulation of defect density and depth in crystals,this originates from the significant increase of density of defects with decreasing depth.(7)Efficient red phosphor Sr4 Al14O25:Mn4?,0.5%Mg was embedded in polymethylmethacrylate(PMMA)and formed a multifunctional coating with a combined ability of luminescent down-shifting and UV-screening as well as waterproof,which can be used for the NiO-based planar inverted organometallic halide perovskite solar cells devices.The power conversion efficiency of the fabricated device with a structure of NiO/CH3NH3PbI3/PCBM/BCP/Au coated with the phosphor layer shows a 10%increase.Importantly,the phosphor layer coating can realize UV-protection as well as waterproof capability,achieving an improved long-term stability of perovskite solar cell devices.At last,the main content of the thesis is systematically summarized,and the perspective of study,development and application of manganese ions doped red luminescent materials in the future is also given.