Preparation And Properties Of Mn⁴⁺ Ion-Activated Oxyfluoride Luminescent Materials

Artificial light sources have experienced the development from incandescent lamps,through halogen lamps,and（compact）fluorescent lamps,to the widely used white light-emitting diodes（WLEDs）.Solid-state light sources with light-emitting diodes（LEDs）and color conversion phosphors as core components have the characteristics of excellent luminous efficiency,high brightness,low power consumption,long lifetime and environmental protection,which have gradually replaced traditional lighting sources.The performance of color conversion phosphors largely determines the color rendering index,correlated color temperature and color rendering stability of light sources.Among them,red phosphors for WLEDs have become a research hotspot in the field of solid-state lighting.Currently,non-rare earth Mn⁴⁺ion-activated luminescent materials have unique photoluminescence properties in the octahedral crystal field,which can be effectively excited by blue LEDs and used to make up for the deficiency of red light components in current WLED devices,thus gaining widespread attention.Since the human eye is more sensitive to the zero-phonon-line（ZPL）emission and strong ZPL emission can improve the color rendering and color purity of WLEDs.Therefore,the study of obtaining luminescent materials with strong ZPL emission is of great importance.However,most of the current Mn⁴⁺-activated luminescent materials have weak zero-phonon transitions,to address this problem,this thesis by selecting oxyfluoride as the matrix of Mn⁴⁺ions,and changes the coordination environment of Mn⁴⁺ions by selecting the composition and structure of the host,thereby realizing the modulation of the luminescence characteristics of Mn⁴⁺ions.In this thesis,three Mn⁴⁺ion-activated oxyfluoride luminescent materials were prepared by co-precipitation method,and their crystal structure,microscopic morphology,coordination environment and spectral characteristics of Mn⁴⁺ions were studied,as well as the relationship between the coordination environment of Mn⁴⁺and its zero-phonon line emission was explored.The main research contents of this thesis include three parts:1.Mn⁴⁺-doped K₂WO₂F₄·H₂O powder samples were prepared by the coprecipitation method.The effects of different Mn⁴⁺ion doping concentrations on the microscopic morphology,phase structure and luminescence properties of the samples were investigated.Under the monitor wavelength of 632 nm,the strongest broad excitation band centered at467 nm is obtained,which is close to the emission wavelength of the blue light chip and can be effectively excited by blue light;under the excitation of 467 nm blue light,narrow emission peaks near 632 nm are obtained.Mn⁴⁺ions are doped into the lattice occupy the W⁶⁺ion sites without a center of inversion and strong ZPL emission is obtained at 623.4 nm.When the doping concentration of Mn⁴⁺ions is 12 mol%,the luminous intensity reaches the maximum value.The decay curve was fitted with a double-exponential function,and the lifetime value was 2.68 ms.D_q/B is 3.99 e V,and Mn⁴⁺is in a strong crystal field environment.2.Microcrystal powders of K₅Nb₃OF₁₈ with/without Mn⁴⁺-doped were synthesized by using a coprecipitation method.The crystal structure and electronic structure of K₅Nb₃OF₁₈,the morphology,crystal structure of K₅Nb₃OF₁₈:Mn⁴⁺,and coordination environment and photoluminescence properties of Mn⁴⁺in K₅Nb₃OF₁₈ were studied.The results show that K₅Nb₃OF₁₈ is a tetragonal structure with space group I4cm（108）.Under the excitation of blue light,Mn⁴⁺ion-activated K₅Nb₃OF₁₈ shows the characteristic emission of Mn⁴⁺around630 nm,due to Mn⁴⁺ion is doped into the K₅Nb₃OF₁₈ lattice and occupies the site of Nb⁵⁺ion with C_4v point symmetry,and there is a strong ZPL emission at 621.5 nm.Structure analysis indicates that Nb⁵⁺ions have more contracted and distorted coordination environments in K₅Nb₃OF₁₈ than in Rb₅Nb₃OF₁₈.These features along with the non-centrosymmetric nature of the sites are considered to response for the intensive ZPL emission.D_q/B=3.90 e V,Mn⁴⁺ion experiences a strong crystal field in K₅Nb₃OF₁₈.The photoluminescence decay curve conforms to change law of the double-exponential function,and the lifetime value ranges from 3.18 to 3.53 ms.3.Mn⁴⁺ion doped and undoped K₃HWO₂F₆ samples were prepared by coprecipitation method.The crystal structure of K₃HWO₂F₆ was analyzed by the XRD and refinement,which show that K₃HWO₂F₆ is a monoclinic structure with space group C2/c（15）.The micro-morphology,structure and luminescence properties of K₃HWO₂F₆:Mn⁴⁺were also studied.The diffraction peak positions of K₃HWO₂F₆ doped with different Mn⁴⁺concentrations are basically the same as those of the undoped one,and there is no impurity phase.Under excitation at 470 nm,the strongest emission peak at 632 nm is obtained;Mn⁴⁺ion is doped into the lattice to form a[Mn F₆]^2-octahedron,and visible ZPL emission is obtained at 620 nm.When the doping concentration of Mn⁴⁺is 2 mol%,the luminous intensity is the highest.