Preparation And Luminescence Properties Of Novel Rare Earth Ion Doped Stannate Fluorescent Materials

Fluorescent materials doped with rare earth ions are widely used in the fields of lighting and display,optical communication and detection.The development and research of rare earth ions doped fluorescent materials with good performance is one of the hotspots in the luminescence field.For the merits of energy saving,environmental protection,long service life,and high efficiency,white light emitting diodes(LEDs),as a new generation of lighting sources,are gradually replacing incandescent lamps and been the fourth generation of lighting sources.Among them,the rare-earth ion-doped fluorescent material is the main component of the fluorescence conversion white light LED(pc-LED),and its performance directly affects the performance of LED devices.This thesis addresses the problems of low conversion efficiency,short service life,and low color rendering performance of pc-LED.Several novel red stannate/tunable light-emitting stannate fluorescent materials were prepared by solid-state reaction method and their luminescence properties were studied.The main research contents are as follows:1.A new tunable light-emitting stannate fluorescent material Sr₃Al₁₀SnO₂₀:x Dy³⁺(0?x?0.04)was synthesized by the traditional high-temperature solid-state method.The crystal structure,phase purity,and chemical composition were investigated via X-ray diffraction Rietveld structure refinement,scanning electron microscopy,and energy dispersive spectrometry.The luminescence spectra indicated that Sr₃Al₁₀SnO₂₀:Dy³⁺not only exhibited characteristic⁴F_9/2?⁶H_J/2(J=11/13/15)inherent transition emissions of Dy³⁺,but also showed an abnormal blue band emission,which was identified through X-ray photoelectric spectroscopy as the T₁?S₀transitions of Sn²⁺,resulting from the valence variation of Sn⁴⁺.The efficient energy transfer from Sn²⁺to Dy³⁺was also confirmed and the transfer efficiency was calculated.Due to the superposition of Sn²⁺emission and Dy³⁺emission caused by the change of valence state,tunable white light from cold to warm white light region can be realized.The color coordinates and correlated color temperature are(0.277,0.333)and 8634 K respectively(0.353,0.404)and 4913 K,respectively.The luminescent and defects formation mechanism as well as the luminescence kinetics were further investigated.Moreover,Sr₃Al₁₀SnO₂₀:Dy³⁺had a high quantum efficiency(?34.6%)and a super-stable thermal stability behavior(82.5%at240°C of the initial integral emission intensity at 30°C)with a large activation energy(?E?0.1654 e V).Finally,a charge-compensation test was performed to further verify the effect of defects on the luminescence property and the related mechanism was discussed.The current work provides a novel method to achieve tunable white-light emission in Dy³⁺single-doped phosphors and the mechanism also has certain reference significance for the potential applications of other rare earth element-doped stannate luminescent materials in the field of lighting and display.2.A new type of red stannate fluorescent material Sr₃Al₁₀SnO₂₀:x Eu³⁺,Li⁺(0?x?0.06)was synthesized by the traditional high-temperature solid-state method.The phase purity of the prepared new red stannate fluorescent material Sr₃Al₁₀SnO₂₀:Eu³⁺,Li⁺sample was determined by XRD test.After SEM,EDS,Mapping and other tests,the morphology and element distribution of the sample can be obtained.Through excitation and emission(PL/PLE)spectra,fluorescence lifetime curves,and thermal quenching spectra,the luminescence performance and thermal stability of the samples were discussed in detail.The test results show that the best excitation wavelength of the prepared new red stannate fluorescent material Sr₃Al₁₀SnO₂₀:Eu³⁺,Li⁺sample is 395 nm,and the emission spectrum shows a narrowband emission centered at 613 nm.The optimal doping concentration of Eu³⁺,Li⁺ions in Sr₃Al₁₀SnO₂₀red stannate fluorescent material is 1%.When the temperature rises to 140?,the emission intensity of the Sr₃Al₁₀SnO₂₀:1%Eu³⁺,Li⁺sample can still reach 85.98%of the initial intensity,and the activation energy is 0.1636 e V.The color purity of Sr₃Al₁₀SnO₂₀:Eu³⁺,Li⁺samples is as high as 98.17%.3.A new type of red-orange stannate fluorescent material Sr₃Al₁₀SnO₂₀:xSm³⁺(0?x?0.06)was synthesized by high temperature solid state method.The phase purity of the sample was confirmed by XRD test.After SEM,EDS,Mapping tests,the element distribution and morphology of the sample can be obtained.The test results show that the emission spectrum under 403 nm excitation is mainly composed of four emission peaks,which belong to the ⁴G_5/2-⁶H_J/2(J=5/7/9/11)transition of Sm³⁺.The optimal doping concentration of Sm³⁺ions in the Sr₃Al₁₀SnO₂₀red-orange stannate fluorescent material is4%.When the temperature rises to 140?,the emission intensity of the Sr₃Al₁₀SnO₂₀:4%Sm³⁺sample can still reach 78.12%of the initial intensity.The activation energy is0.1526 e V.According to CIE coordinate diagram,Sr₃Al₁₀SnO₂₀:xSm³⁺(0?x?0.06)series samples are located in the red and orange light region.4.A series of novel red-emitting stannate phosphors Sr₂SnO₄:x Pr³⁺(0?x?0.01)are developed through high temperature solid phase method.The crystal structure and phase purity are identified by X-ray diffraction and Rietveld structure refinement.The microstructure and element composition are characterized through scanning electron microscopy and energy dispersive spectrometer.In order to explain the luminescence characteristics in detail,the photoluminescence excitation and emission spectra,attenuation life and color coordinates of Sr₂SnO₄:x Pr³⁺(0?x?0.01)series phosphors are studied.The results show that Sr₂SnO₄:x Pr³⁺(0?x?0.01)phosphors have prominent excitation about 450 nm and can show red emissions peaking at 623,652,714 and 738 nm,respectively,ascribed to the³P₀–³H₆,³P₀–³F₂,³P₀–³F₃and³P₀–³F₄transitions of Pr³⁺ions.The influences of the content of Pr³⁺as well as charge compensation by co-doping with M⁺(Li⁺/Na⁺/K⁺)ions on the luminescent properties were discussed.The result reveals that codoping Li⁺ions can simultaneously increase the emission intensity and thermal stability.Furtherly,the mechanism of charge compensation and thermal quenching property are well studied through the temperature dependent decay curves and emission spectra.