Investigation For Long Wavelength Luminescent Materials:Preparation And Optical Properties

Rare earth doped long afterglow materials and white LED phosphors are green and clean energy materials,which have attracted the attention of researchers in various fields,due to their excellent luminescent properties and a wide range of applications.In this dissertation,the luminescent properties of the as-prepared long afterglow materials and white LED phosphors were optimized by co-doping.The details are as follows:1.Ca₂Sn O₄:Sm³⁺long afterglow materials:In this part,a series of Sm³⁺single doped and Sm³⁺together with Bi³⁺,Yb³⁺,Al³⁺,La³⁺,Zn²⁺,Cd²⁺,Mg²⁺,Ba²⁺,Sr²⁺,Zr⁴⁺ions co-doped reddish orange afterglow materials were prepared by high temperature solid state reaction in air atmosphere.The afterglow brightness decay curves show that the afterglow time of single doped sample can reach 10 hours（the time required for afterglow brightness larger than 0.32 mcd/m²）.The afterglow properties of co-doped samples varied widely.The afterglow duration of Sm³⁺and Zr⁴⁺ions co-doped materials was well improved and the afterglow can last longer than 14 hours,while the afterglow of Sm³⁺and Bi³⁺ions co-doped samples was severely quenched.Thus,the effects of co-doping La³⁺,Zn²⁺,Ba²⁺,Zr⁴⁺,Bi³⁺,Yb³⁺and Al³⁺on the afterglow luminescence properties of Ca₂Sn O₄:Sm³⁺materials were systemically investigated with thermal emission spectroscopy and afterglow curves.Co-dopant La³⁺,Zn²⁺,Ba²⁺,Zr⁴⁺caused an increase in the shallow trap concentration,which was favorable for the afterglow.However,the introduction of Bi³⁺,Yb³⁺and Al³⁺decreased the shallow trap concentration and quenched the afterglow.2.Red CaWO₄:Eu³⁺phosphors for w-LEDs:The red CaWO₄:Eu³⁺phosphors for w-LEDs were successfully synthesized via high temperature solid state method in air atmosphere.The phase structure,photoluminescence properties and thermal stability were investigated detailedly.Afterwards,Mg²⁺and Sr²⁺were introduced into CaWO₄:0.10Eu³⁺to induce the crystallographic parameters and crystal symmetry changes of Eu³⁺ions in the CaWO₄ host.All of the as-prepared samples,especially Ca_0.65Mg_0.20Sr_0.05WO₄:0.10Eu³⁺phosphors exhibit an extremely enhanced red emission peaking at 616 nm originating from ⁵D₀→⁷F₂ transition of Eu³⁺under the 392 nm n-UV excitation.Enhanced red emission,broadband excitation spectra（from 200 to 600 nm）,strong ultraviolet absorption matched well with n-UV LEDs chips（350-420 nm）,excellent thermal stability and high color purity（the R/O value is up to 7.52）indicate that as-prepared Ca_0.65Mg_0.20Sr_0.05WO₄:0.10Eu³⁺sample can be a potential candidate red phosphor for n-UV white light-emitting diodes.