A₂MgTiO₆: Mn⁴⁺(A=La,Y,Gd) Low-temperature Synthesis And Synthesis Of Double Perovskite Red Phosphor Research On Its Luminous Performanc

White LED?w-LED? has been widely used in indoor lighting because of its excellent characteristics such as high luminous efficiency,good thermal stability,energy saving and environmental protection.However,commercial w-LED generally show low color rendering index and high color temperatur due to the lack of red light,and adding red phosphors is one of the most important methods to improve LED luminescence performance.Mn⁴⁺ activated red phosphors can be excited by the light emitted by commercial blue light LED chips and emit red light.Therefore,Mn⁴⁺ doped red phosphors can be directly used to improve the deficiency of red light of LED and obtain warm white LED with high color rendering index.In this thesis,a series of Mn⁴⁺ doped double perovskite A₂MgTiO₆:Mn⁴⁺?A=La,Y,Gd?red phosphors were synthesized via molten salt method at lower temperature.The crystal structure,phase purity,microstructures,photoluminescence and thermal stability of the phosphors were studied.The main research contents and results of this thesis are as follows:?1?Previous studies have shown La₂MgTiO₆:Mn⁴⁺?LMT? red phosphors were synthesized mainly through high temperature solid phase method under the reaction temperature of 1350? above.In this thesis,a series of Mn⁴⁺ doped La₂MgTiO₆ red-emitting materials with highly efficient red emission have been successfully prepared by molten salt assisted method which LiCl acting as molten salt at a relatively low temperature.Experimental results indicate that the synthesis temperature of the Mn⁴⁺-doped La₂MgTiO₆ by molten salt method is only 800? while the traditional solid phase method requires 1350?.The morphology and particle size of phosphors can be well controlled by adjusting the reaction temperature and the amount of molten salt.The thermal stability and quenching mechanism of phosphors were studied by temperature dependent emission spectra,which demonstrated that LiCl is benefit to improve the thermal stability of the Mn⁴⁺ activated La₂MgTiO₆ phosphors.?2?Considering that A₂BB'O₆ has similar physicochemical properties,it is possible to prepare other dual-perovskite phosphors by molten salt method.In this chapter,Y₂MgTiO₆:Mn⁴⁺?YMT? red phosphor was successfully prepared by molten salt method using LiCl as molten salt.The experimental results show that the YMT of the pure phase can be obtained with the oxide as the raw material when the sintering temperature is 1100?,which is higher than the preparation temperature of LMT in the first chapter,but 300? lower than the lowest sintering temperature of 1400? already reported.In addition,the prepared materials have controllable morphology and excellent luminescence characteristics.?3?A careful comparison of the preparation conditions of LMT and YMT shows that the difference in ionic radius of A site(Y³⁺and La³⁺) will result in a 300? difference in synthesis temperature,which is probably due to the difference in radius between the two cations.In order to further verify the influence of ion radius on the synthesis temperature,Gd³⁺ ions with radius between Y³⁺ and La³⁺ were used in this chapter as A ion in double-perovite structure A₂BB'O₆.The pure phase Gd₂MgTiO₆:Mn⁴⁺?GMT? red phosphor material was synthesized by molten salt method with LiCl as molten salt at 800?.The results show that the pure phase LMT and GMT material can synthesize at 800?,indicating that the effect of ion radius on the synthesis temperature is not as large as expected.It is worth mentioning that the GMT sample prepared has excellent luminescence characteristics,which provides the basis for its application in LED.Finally,the fluorescence properties and thermal stability of A₂MgTiO₆:Mn⁴⁺?A=La,Y,Gd? phosphors were compared.The results showed that LMT,YMT and GMT phosphors had excellent optical properties and high thermal stability.