Synthesis Of Novel Mn⁴⁺-activated Oxyfluoride Red Phosphors And Their Luminescence Properties

White light-emitting diode（LED）has been widely used in people’s daily life because of its long service life and small size.Adding red component is considered to be the key to obtain white LED with low color temperature and high color rendering index.In recent years,Non-rare-earth transition metal ion Mn⁴⁺doped fluoride red phosphor has attracted extensive attention due to its broad band blue absorption and narrow band red emission and has rapidly developed into a new red candidate material of white LED.However,poor heat resistance and long fluorescent life problems limiting its further application.The local operating temperature of white LEDs can reach more than 150 C,and the thermal quenching of fluoride phosphors will lead to a serious decrease in light efficiency.At the same time,for commercial phosphors used as backlights for（liquid crystal display,LCD）,long fluorescence lifetime（usually>5 ms）will lead to image retention.Therefore,it is still a great challenge to obtain Mn⁴⁺activated fluoride phosphors with high efficiency and short fluorescence lifetime.In this paper,innovatively,by introducing new anions O^2-into the fluoride matrix to adjust the crystal structure and the local environment of Mn⁴⁺.The aim is to design and synthesize novel red phosphors with low cost and better optical properties and explore its luminescent properties.Finally,the application of high efficiency and short fluorescence lifetimes of the prepared oxyfluoride red phosphor in high-quality white LED lighting and fast response backlight display was realized.The main research contents are as follows:（1）A novel CsMoO₂F₃:Mn⁴⁺oxyfluoride red phosphor was synthesized by coprecipitation at room temperature.The Cs MoO₂F₃:Mn⁴⁺phosphor exhibits an orthorhombic structure with an Imma space group,and Mn⁴⁺ions tend to occupy the lattice sites of Mo⁶⁺in[MoO₂F₄]^2-octahedron.Cs MoO₂F₃ lattice has enough energy levels to hold Mn⁴⁺ions.A series of samples with Mn⁴⁺concentration gradient was prepared,and the best doping concentration of Mn⁴⁺was3.88 mol%.Under the excitation of 468 nm,Cs MoO₂F₃:Mn⁴⁺phosphor appeared a series of strong narrow band red light emission peaks at about 633 nm,QE was 54%,Cs MoO₂F₃:Mn⁴⁺phosphor had super high color purity 99.58%.Cs MoO₂F₃:3.88%Mn⁴⁺phosphor has obvious negative heat quenching phenomenon.The total luminous intensity at 275 K was increased by about 540%compared with that at 25 K.When the temperature from room temperature rises to423 K（150℃）,the relative luminous intensity increases by 129.3%.The results show that the intensity of the light emission can still be kept 91.5%at room temperature when the temperature reaches 200℃.The results show that the color drift（ΔE）is only～33.9×10^-3when the temperature rises from 298 K to 473 K,which is better than commercial nitride red powder.We package the phosphor with commercial YAG:Ce³⁺and blue light chip to obtain a warm white LED with low color temperature（3983 K）,high color rendering index（Ra=81.3）.The luminous efficiency of the LED is 68.58 lm/W under 20 m A driving current.With the driving current from 20 to 120 m A,the phosphors showing good stability.Cs MoO₂F₃:Mn⁴⁺is expected to be a commercial red phosphor with high power and high performance WLED,which probably propose a feasible strategy to exploit stable non rare earth red luminescent materials for warm WLED.（2）A novel single-phase oxyfluoride red phosphor Cs₂MoO₂F₄:Mn⁴⁺,has been successfully prepared by a co-precipitation method with a certain molecular ratio of CsF and MoO₃ under mild conditions.The crystal structure of the red phosphor is the same as that of Cs MoO₂F₃:Mn⁴⁺.Mn⁴⁺occupies the Mo⁶⁺site in the center of octahedron and enters into the main lattice.Mn⁴⁺with smaller radius will cause a small number of vacancy defects,resulting in lattice shrinkage.Mn⁴⁺in Cs₂MoO₂F₄matrix is affected by strong crystal field strength and electron cloud rearrangement.Under blue excitation,Cs₂MoO₂F₄:Mn⁴⁺oxyfluoride red phosphor shows a series of clear red narrow-band emission peaks at 634 nm,and obvious zero phonon line can be observed at～619 nm.The optimal doping amount of Cs₂MoO₂F₄:Mn⁴⁺is1.12%,the color purity is 99.38%,and the quantum efficiency is 77.31%.and the decay curves fit well to a single exponential decay model.The fluorescence decay curve of Cs₂MoO₂F₄:Mn⁴⁺is in good agreement with the single exponential decay model.The fluorescence lifetime of the synthesized phosphors is short,ranging from 3.18 ms to 2.46 ms.The phosphor has good stability at low temperature.With the increase of temperature,the luminescence intensity began to decrease.When the relative intensity decreased to half,the temperature was 377 K.A white LED device was prepared by using the synthesized Cs₂MoO₂F₄:Mn⁴⁺phosphor as the red component andβ-Sialon as the green component.The luminous efficiency of the LED was114.70 lm·W^-1,and the color gamut was 109.1%of the NTSC value.Cs₂MoO₂F₄:Mn⁴⁺is expected to be a commercial red phosphor for fast response backlight display.