Preparation And Properties Of CdSiO₃:Mn²⁺, RE³⁺（RE=Sm,Dy, Eu, Tb, Nd, Er, Ho） Phosphors

Long-lasting phosphors is a kind of energy-storing materials. The materials canabsorb sunlight or artificial light, store the energy, and then release the energy asvisible light, which lead to a long lasting afterglow in the darkness. They have beenwidely used in many fields, such as safety indicators, lighting in emergency situations,instruments in automobiles and luminous paint, and so on. Most long-lastingphosphors are based on sulfide, aluminates, or silicate hosts. Compared with the otherhosts, silicate phosphors are more attractive because of their multi-colorphosphorescence and resistance to acid, alkali and oxygen.Recently, considerable attention has been devoted to CdSiO₃due to its crystalstructure, which is expected to be a one-dimensional chain of edge-sharing SiO4tetrahedrons. As a result of this structure, it is very easy to create traps with someextent density during the high-temperature synthesis process. Furthermore, the trapsdistributed in host lattice randomly can serve as the role of energy carrier moreeffective in this low-dimensional compound, which provide possibility of producinghigh efficient luminescence material. So, CdSiO₃is a promising silicate host.In this study, new long-lasting CdSiO₃:Mn²⁺, RE³⁺（RE=Sm, Dy, Eu, Tb, Nd, Er,Ho） phosphors were synthesized by solid-state reaction method and sol-gel method,respectively. The main results of the research work are as follows:1. The long-lasting phosphor CdSiO₃:Mn²⁺, RE³⁺（RE=Sm, Dy, Eu, Tb, Nd, Er,Ho） was synthesized at1050°C via solid-state reaction method. Effects of the contentof Mn²⁺and RE³⁺on the luminescent properties of phosphor CdSiO₃:Mn²⁺, RE³⁺wereinvestigated by means of photoluminescence （PL） spectra, the afterglow intensitydecay curves, afterglow spectra and the thermoluminescence （TL） spectra. Throughthe mentioned measurements, the optimal ratio of Mn²⁺/RE³⁺could be found. To thedifferent rare earth ions RE³⁺, the optimal ratio was different. Due to the difference inco-doped rare earth ionic radii, it could vary greatly in trap density and trap depth which were caused by the different defects deriving from RE³⁺ions occupying theCd²⁺sites in the CdSiO₃:Mn²⁺host. In addition, the luminescence characteristicsabout the host CdSiO₃, Mn²⁺doped-CdSiO₃:Mn²⁺, Mn²⁺, RE³⁺codped-CdSiO₃:Mn²⁺,RE³⁺were also be studied systematically. Although the emission of some rear earthions could be found to some RE³⁺codoped CdSiO₃:Mn²⁺, RE³⁺in the emissionspectra, the emission of Mn²⁺（587nm） was detected mainly in the afterglow spectra,corresponding to the4T1g（G）â†'6A1g（S） transition of Mn²⁺ions occupying the Cd²⁺sites in the lattice, which indicated that the Mn²⁺ions were the activators.Furthermore, the afterglow intensity of CdSiO₃:Mn²⁺, RE³⁺（RE=Sm, Dy, Eu, Tb, Nd,Er, Ho） was higher than CdSiO₃:Mn²⁺, indicating that the RE³⁺ions in the samplesplayed the role of assistant activators.2. CdSiO₃host was prepared by sol-gel method. The prepared samples werecharacterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）respectively. The effects of the reacting temperature and the calcining time on phaseformation and morphologies were investigated. With the temperature increasing, theimpurity peak was lowing, the intensity of the main diffraction peaks showed thetendency of higher first and lower later, which indicated that the crystal degree of thepowder was affected greatly by the calcining temperature. In addition, during theprocess of temperature increasing, the phenomenon of the sample first melted andthen refroze occurred. When the synthesis temperature was up to1100℃, the productturned to glass phase and could not be removed from the wall of ceramic crucible, so1050℃was the highest temperature for the samples to be prepared. If the sampleswere kept for too long time, the glass phase would also be found in the samples. As acomparison, the sample was also prepared by solid-state reaction method and the rawmaterials were fired at1050℃for5h to get the product. While the single phaseCdSiO₃powders with good homogeneity and good crystallization could be obtainedby sol-gel method at900°C for2h, which implied the sol-gel method is a promisingmethod to prepare the samples at relatively lower temperature.3. The Mn²⁺and RE³⁺（RE=Sm, Dy, Eu, Tb, Nd, Er, Ho） codoped CdSiO₃:Mn²⁺,RE³⁺phosphors were prepared by sol-gel method. Both Mn²⁺and RE³⁺dopant concentrations relative to the host compound were chosen based on the optimal ratioof Mn²⁺/RE³⁺derived from solid-state reaction method. The effects of the calciningtemperature and the soaking time on the afterglow properties were studiedsystematically. Furthermore, solid-state reaction method was also be used to make acomparison in the afterglow properties of the prepared phosphors. With thetemperature increasing, the volatilization of Cd²⁺increased. The defects would bemore and the trap density would be higher. As a result, the afterglow time for thesamples became longer. On the other hand, with the temperature increasing, thecrystal of the CdSiO₃would grow better. It was easier for Mn²⁺and RE³⁺to occupythe Cd²⁺to form more luminescence centers and more traps, which was better toimprove the luminescence properties. And when the samples were prepared at1050°C,within some time, with the time prolongation, the crystal of the CdSiO₃would growbetter. The afterglow performance for the samples would be better. But if the sampleswere kept too long, the glass phase in the sample would be more and the afterglowperformance would be worse.Through the experiments and analysis, the purpose of this work was to betterunderstand the afterglow mechanism, optimize the processing technology and finallyimprove the afterglow performance of the samples.