Design And Study Of New Phosphors For White LED Lighting And Display

The development of solid state lighting,represented by the fourth generation lighting and display technology,puts forward higher requirements for the performance of phosphors.Single host phosphor materials with high color rendering index,high efficiency and high thermal stability,high efficiency,narrowband emission phosphor materials and morphologically controllable phosphor materials have become the current research hotspots.In order to overcome the shortcomings of phosphors used in white LED,several kinds of single-host multi-color emission phosphors and high-efficiency narrow-band emission phosphors were synthesized.Several methods to synthesize morphologically controllable and multi-components-colors phosphors were developed.At the same time,the crystal structure,luminescence performance and energy transfer process,particle size distribution,micro-morphology and so on of phosphors were also studied in depth.The specific research contents are as follows:?1?Ce³⁺/Tb³⁺,Ce³⁺/Mn²⁺,Ce³⁺/Eu²⁺and Eu²⁺/Mn²⁺were selected as activator combinations,by adjusting the doping ratio of sensitizer and activator ions,the control from blue light to green,white and yellow lights,from cyan light to white and yellow lights were realized in Sr₃Gd₂?Si₃O₉?₂?SGSO?-based phosphors.The interaction mechanism of energy transfer between activator ions was discussed by means of fluorescence spectra and lifetimes.By introducing the sensitizer Ce³⁺,Tb³⁺and Mn²⁺,Eu²⁺all show better thermal stability than that of single doping sample.Their luminescence intensities at 423 K are 72.3%,86.1%and 85.6%in comparison to that at room temperature.In addition,Mn²⁺acts as a structural regulator,which regulates the luminescence properties of Eu²⁺and Eu³⁺by changing the structure and polyhedral distortion occupied by Eu²⁺and Eu³⁺in SGSO.At lower Mn²⁺concentration,SGSO:Eu,Mn exhibits good thermal stability and slight color shift,while at higher Mn²⁺concentration,the phosphor exhibits good temperature sensitivity.?2?Mg²⁺,Zn²⁺cationic ions and Gd³⁺-Na⁺ion-pair substituted composite silicate Na₂Ba₆?Si₂O₇??SiO₄?₂?NBSS?phosphors were designed and synthesized by using Eu²⁺as activator ion.By changing the doping ratio of Mg²⁺,Zn²⁺and Gd³⁺-Na⁺,the emission color of NBSS:Eu²⁺can be controlled in blue and cyan regions.Combined with the changes of crystal structure and spectra of NBSS:Eu²⁺,xMg²⁺/yZn²⁺/z(Gd³⁺-Na⁺),it can be found that the main reason for the change of emission peak position of Eu²⁺is that the change of matrix composition and content changes the preferential position of Eu²⁺in different cation sites.In addition,the Mg²⁺and Zn²⁺substitutions can obviously improve the thermal stability of Eu²⁺,and Mg²⁺has better effect on improving the thermal stability than Zn²⁺and Gd³⁺-Na⁺,and the change of thermal stability of Eu²⁺is closely related to the distortion of crystal structure.?3?Sr₂MgAl₂₂O₃₆?SMAO?:Mn²⁺narrow-band green emission phosphors were synthesized by using the hexagonal and high symmetry crystal structure SMAO as matrix.Under the excitation of 450 nm,SMAO:Mn²⁺emits bright green light in the range of 485 nm-590 nm,with the maximum emission peak at 518 nm and a FWHM of26 nm.The lattice vibration intensity of several kinds of phosphors was studied by FTIR measurement.It can found that the narrow-band emission is closely related to the symmetry of the matrix structure.In addition,the high symmetrical coordination environment around Mn²⁺and there are only one kind of Mg²⁺site in the matrix lattice for Mn²⁺doping are beneficial to the narrow-band emission of Mn²⁺.The SMAO:20%Mn²⁺sample has good thermal stability,and it can still maintain 81.91%of the initial strength measured at 298 K at 473 K.When SMAO:Mn²⁺,K₂SiF₆:Mn⁴⁺and GaN-based chips are integrated into white LED devices,about 127%of the ultra-wide NTSC gamut can be displayed.In addition,by introducing Mn²⁺and Mn⁴⁺into Mg²⁺and Al³⁺lattices,both Mn²⁺and Mn⁴⁺emit narrow-band green and red lights simultaneously in the SMAO host.Under the excitation of 385 nm,SMAO:Mn²⁺,Mn⁴⁺samples can simultaneously produce a green emission in the range of 485 nm-590 nm and a red emission in the range of 630 nm-730 nm.The maximum emission peak of green light is about 518 nm,FWHM is 26 nm,while the maximum emission peak of red light is about 659 nm and FWHM is 42 nm.?4?By using Gd_0.99Eu_0.01?OH?₃ nanorods as precursors,flake,flower and spherical morphologies of Gd_0.99Eu_0.01BO₃ red phosphors were successfully synthesized.The increase of NaOH concentration in colloidal solution and the decrease of PEG?20000?content in the treatment of Gd_0.99Eu_0.01?OH?₃ will gradually transform the morphology of Gd_0.99Eu_0.01BO₃ from sphericall to flower-like and flake-like shape.By investigating the XRD spectra and corresponding SEM images of intermediate products obtained at different reaction time intervals,the formation of Gd_0.99Eu_0.01BO₃ products with differentmorphologieswassummarizedasakineticallycontrolled dissolution-recrystallization mechanism.The emission spectra of Gd_0.99Eu_0.01BO₃samples are characteristic emission peaks of Eu³⁺ions.Moreover,the activating agent ions obtained by this method have a large number of nano-scale surface positions,resulting in lower local environmental symmetry of Eu³⁺,which greatly improves the emission ratio of red light to orange light.In this work,a method of synthesizing micro-and nano-materials with controllable morphology and stable performance using mesoporous SiO₂ as reaction vessel was proposed and designed.In this paper,Bi_0.96Eu_0.04PO₄ nanospheres with high luminescent efficiency were successfully synthesized by the above methods using Bi_0.96Eu_0.04 nanospheres as precursors.Compared with one-step synthesis of Bi_0.96Eu_0.04PO₄,this method not only has controllable spherical morphology,but also has higher energy transfer efficiency from matrix to Eu³⁺.The preparation method can also be extended to design and fabricate micro-and nano-materials with controllable morphology in other material systems.?5?Two design concepts of multi-component and multi-color phosphors were proposed.The first process includes preparation of homogeneous precursors,coating mesoporous SiO₂ on the surface of precursors,treating intermediate products with metal solution and calcination.Y₂Si₂O₇:Ce³⁺,Eu³⁺@Zn₂SiO₄:Mn²⁺series samples were successfully synthesized by using Y?OH?CO₃ as precursor.XRD,SEM and TEM analysis show that the samples present hollow spheres with shell thickness about 100nm,mainly consisting of two phases:Zn₂SiO₄ and Y₂Si₂O₇.This Y₂Si₂O₇@Zn₂SiO₄structure can accommodate a variety of luminescent activated ions(Ce³⁺,Mn²⁺,Eu³⁺),and full spectrum emission under a single wavelength excitation can be achieved.In addition,in the Y₂Si₂O₇@Zn₂SiO₄ structure,the emissions of Ce³⁺,Eu³⁺and Mn²⁺exhibit excellent thermal stability due to interface defects and energy transfer from defect level to activator at high temperature.The second process includes the preparation of phosphors with uniform morphology and the deposition of nanostructured g-C₃N₄ on the surface of phosphors by vapor deposition.Y₂O₃:Tb³⁺,Eu³⁺@g-C₃N₄ and Y₂O₃:Tb³⁺,Eu³⁺@mSiO₂@g-C₃N₄ phosphors were successfully synthesized by using Y₂O₃ and Y₂O₃@mSiO₂ microspheres as precursors.Y₂O₃ and Y₂O₃@mSiO₂ microspheres were evenly coated with an 8 nm thick amorphous g-C₃N₄layer.Under the excitation of 368 nm,Y₂O₃:Eu³⁺,Tb³⁺@g-C₃N₄ samples contain the characteristic emission peaks of Tb³⁺and Eu³⁺,and blue emission peak of g-C₃N₄ at 463nm.In addition,there was an effective energy transfer process from g-C₃N₄ to Tb³⁺and Eu³⁺.By controlling the coating quality of melamine,the luminescent color of the phosphor can be controlled from blue light to white and yellow light.These two methods can also be extended to the design and preparation of other morphology controllable multi-component materials.