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Synthesis Of Red Long Lasting Phosphors By Solid State Reaction At Low Temperature And Their Luminous Properties

Posted on:2009-01-11Degree:MasterType:Thesis
Country:ChinaCandidate:F L SongFull Text:PDF
GTID:2121360272457883Subject:Physical chemistry
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This paper outlines unique characters and the present developing situation of red long afterglow luminescent materials, introduced the common several preparations method: the high temperature solid state, the sol - gel, the combustion method and so on.We combined the virtues of combustion and high temperature solid state (solid state at low temperature) to synthesize some optical materials. Several long afterglow red phosphors materials are synthesized mainly by solid state at low temperature and their luminescent characteristics are also investigated.1.Using H3BO3 and CO(NH2)2 as auxiliary reagents,long afterglow phosphors Sr2MgSi2O7:Eu2+, Dy3+were synthesized by solid-state reaction at low temperature. Photoluminescence spectra showed that Sr2MgSi2O7:Eu2+, Dy3+phosphors hold a better afterglow properties when the molar ratio of Eu to Dy was 2:1. When a certain amount of Nd ion was introduced and employed NH4NO3 and citric acid instead of CO(NH2)2, the phosphors can emit red light. The analytical results indicated that there is a broader emission band centered at between 502 nm and 635 nm when excited by 340 nm, which is ascribed to the luminescent emission of the Eu3+. Powder X-ray diffraction (XRD) data showed that both of the phosphors are single-phase Sr2MgSi2O7 structure and Transmission electron microscopy (TEM) showed that the average particle sizes were about 25 nm and 100 nm, respectively.3. Long afterglow phosphors Eu2+-activated Ca2ZnSi2O7 phosphors were prepared by solid-state reaction at low temperature. Phase-pure crystalline Ca2ZnSi2O7 can be obtained at 600℃, a much lower temperature than in conventional solid-state reactions and the preparation process of Ca2ZnSi2O7 was simple. The obtained phosphors showed three emission peaks at 480,580 and 620 nm, and they were due to the different Eu luminescent centers in Ca2ZnSi2O7 host, the phosphors would emit blue-green lights when the excitement wavelength was 405nm, but when the excitement wavelength was 233nm the phosphors can emit reddish light. Long afterglow was observed although the phosphor showed faint persistence. Auxiliary activator RE3+(RE=Dy, Nd, Tm) would create some new defects in these compounds at lower traps levels and enhanced their luminescent properties.3. A new type of red long afterglow phosphors with a general formula Ba2MgSi2O7 Eu3+ ,RE3+(RE=Dy, Tm, Ce, Er,Nd) have been prepared by solid-state reaction at low temperature. The reaction time was 5 min. It is indicated that compared with the traditional high temperature solid-state reaction, the products prepared by the modified solid-state reaction are more easy to comminute, and more pure. The reaction time is very short and the formation temperature of the phosphors is very low. Excitation peak of the products value are 248nm and 405nm. Emission peak value are 595nm and 620 nm which indicate that it is the typical 5D0→7F2 transition of Eu3+ .When excited by UV(λexc=248nm), the co-doped materials(Eu3+=RE3+=6%) restrain the emission of Eu3+. However, when excited by 405nm, the co-doped materials such as Tm3+,Dy3+,Ce3+ could obviously enhance the emission intensity of Eu3+ without changing the position of emission peak ,but the Nd3+, Er3+ weaken it.4. Using tetra-n-butyl titanate and nitrates as starting materials, red persistent phosphors CaTiO3: Pr have been successfully synthesized by modified solid-state reaction. In order to improve the luminescent properties of the phosphors, boric acid as flux material and aluminum ion as charge compensator were added in, and the influences of partially replacing Ca2+ in CaTiO3 with Mg2+ or Zn2+ on the long persistent properties were studied. The analytical results showed that a certain quantity of boric acid, Al3+, Mg2+ or Zn2+ was effective in improving the photoluminescence intensity of CaTiO3: Pr phosphors, and the optimum molar ratios of boric acid and Al3+ to Ca2+ were about 0.3% and 0.1% respectively. The photoluminescence brightness and decay curves showed that the samples Ca0.8Zn0.2TiO3: Pr with 0.l% Al3+ and 30% boric acid obtained at the sintering temperature of 900℃exhibited the optimal luminescent properties.5. ZnCo2(C2O4)3?6H2O nanocrystal was prepared by a one-step solid state reaction method at room temperature under ambient conditions using oxalic acid as a chelating agent。Adding oxalic acid to the mixture of zinc acetate dihydrate and cobalt acetate tetrahydrate, grinding and subsequently calcining the precursor at different temperatures, the pink precursor was attained. Thermogravimetric analysis and Differential scanning calorimetry have been used to study the thermal behaviors of the precursor, which reveal the precursor is compound. Powder X-ray diffraction data show that the sample obtained by heating the precursor between 350°C and 550°C for 3h is single-phase cubic material having the spinel-type structure, which can be confirmed by Infrared spectra. Transmission electron microscopy images show that the grain size of the precursor and the products are about 50nm and 20nm, respectively.
Keywords/Search Tags:Red long-afterglow, Solid-state reaction at low temperature, Nanoparticles, Optical properties
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