Synthesis And Optical Properties Of Red To Green Emitting C12A7:Sm,Tb Conductive Phosphors Without Encaged OH~- Anions

The low-voltage field emission display?FED?has potential applications in the extreme display conditions such as high temperature due to its unique advantages such as wide temperature range,fast response and high integration.The related working principle is as follows:the electrode accelerates the electrons emitted by the cathode and the emissions with various colors are obtained by bombarding the phosphors coating on the anode.In particular,the color rendering performance of low-voltage FED is directly related to the conductivity of the phosphors.For example,for the phosphors with low conductivity,during the operation of display,there exists the charge accumulation effect and it leads to the decreased luminescence.Therefore,it is a hotspot on how to prepare oxide-based conductive phosphors with resistance to electron beam bombardment for low-voltage FED.Recent researches have shown that under the low-voltage electron beam excitation,rare earth ions(Sm³⁺,Gd³⁺,Ce³⁺,Dy³⁺)doped C12A7 conductive phosphors with special cage structure can realized red,ultraviolet and white-light emissions due to their good conductivity,strong luminescence and resistance to electron beam bombardment.However,for C12A7based conductive phosphors prepared in H₂ atmosphere,the created encaged OH^-will quench the luminescence of rare earth ions.To further improve the cathodoluminescence intensity,it is still an unresolved issue on how to prepare rare earth doped C12A7 conductive phosphors without encaged OH^-.In this dissertation,Sm³⁺doped C12A7:x%Sm³⁺conductive phosphors with different concentrations?x=0.1,0.3,0.5,0.7,1.0?were prepared in a carbon-embedded semi-closed crucible by melt-solidification method.It is found that,for each of these samples,there exist four emission peaks at 564,601,648 and 709 nm(?_ex=404 nm),respectively,originating from the ⁴G_5/2?⁶H_J/2?J=5,7,9,11?transitions of Sm³⁺.For the sample with x=0.3%,the strongest luminescence can be obtained.For the C12A7:0.3%Sm³⁺sample prepared by melt-solidification method,electrons and oxygen ions trapped in the cage can be detected,but there is no OH^-ion trapped in the cage.The encaged electron concentration was calculated to be 8.5×10¹⁹cm^-3.The CL intensity of the sample reaches a maximum when it was annealed at225°C for 50 min in air.In addition,compared to the conductive C12A7:Sm³⁺sample prepared in hydrogen ambient,the sample without encaged no OH^-groups has larger conductivity,and its CL intensity is also enhanced by 2-3 times?CIE coordinate of?0.60,0.40??.Meanwhile,for C12A7:0.3%Sm³⁺,y%Tb³⁺?y=0.1,0.3,0.5?conductive phosphors with different Tb³⁺doping concentrations were prepared by melt-solidification method,the emissions from red to green can be tuned.The infrared transmission spectrum of the sample do not exhibit the absorption peak at 3550 cm^-1,indicating that there is no OH^-ions trapped in the cage in the phosphors.The electron paramagnetic resonance spectroscopy of the sample showing an intense signal peaked at 3420 Gauss at low temperature?80 K?and the diffuse reflectance absorption spectrum showing the absorption peak around 2.72 eV indicate that there exist encaged electrons in these samples(encaged electron concentration is 8.8×10¹⁹cm^-3).The characteristic emission peaks of Sm³⁺and Tb³⁺appear when these samples are excited at 377 nm.The emission peaks at 440-460 nm can be attributed to the ⁵D₃?⁷F₄transition of Tb³⁺and the peaks at 488,541,564,585,601,648 and 709 nm can be ascribed to the ⁵D₄?⁷F₆(Tb³⁺),⁵D₄?⁷F₅(Tb³⁺),⁴G_5/2?⁶H_5/2(Sm³⁺),⁵D₄?⁷F₄(Tb³⁺),⁴G_5/2?⁶H_7/2(Sm³⁺),⁴G_5/2?⁶H_9/2(Sm³⁺),and ⁴G_5/2?⁶H_11/2(Sm³⁺)transitions,respectively.As the Tb³⁺doping concentration increases,a shift of the color coordinate position from red to green region can be observed.In particular,the color coordinate of the C12A7:0.3%Sm³⁺,0.3%Tb³⁺phosphor is located at the warm white light region?0.40,0.40?.In addition,for the conductive and insulating C12A7:Sm³⁺,Tb³⁺mixed phosphors,the CL intensity is enhanced.