Preparation and Luminescence Properties of Strong Covalent Silicon Nitride Based Phophors

Author:Wang Yang

Supervisor:zhu ying chun


Degree Year:2018





In this dissertation,the Eu doped M2S5N8(M=Ca,Sr)with strong convalent phosphors was select as the research object.The luminescent property,crystal growth and luminescene mechanism of the phosphors were studied.Three types of red light emitting M2S5N8 phosphors,including:(1)Sr2S5N8 phosphors,(2)Ca2S5N8 phosphors(3)Sr2-x Cax Si5N8 phosphors.The innovative results of this thesis were summarized as follows.The red-emitting Sr2Si5N8:Eu2+ phosphors have been synthesized in a new facile process using(oxy)nitride precursors by inductive calcination under N2 atmosphere at ordinary pressure.Different from the prevailing methods,lower cost raw materials,simpler pretreatment,without harsh conditions and a shorter reaction time are achieved.It was found that red-emitting Sr2Si5N8:Eu2+ phosphors were synthesized with high crystallinity and purity after 1-hour inductive calcination.The formation mechanism was characterized by XRD,SEM,TEM and Fluorescence microscopy.It was demonstrated that a hexagonal mesophase of Sr-doped α-Si3N4 was primarily formed in the reaction process,which transformed into the final product of the orthorhombic Sr2Si5N8:Eu2+ phosphors.During the reaction process,the color of the samples transforms from greenish-yellow to orange and eventually to red.The as-prepared phosphors have a wide excitation in the range of 250~570 nm which matches blue light chips and give a red-light emission peaking at 610 nm.The results indicate a promising prospect for a simple,efficient and inexpensive way to prepare Sr2Si5N8:Eu2+ phosphors for blue/UV-based warm-white LEDs and other fluorescent applications.Eu2+-doped Ca2Si5N8 phosphors were synthesized in a facile one step route using raw materials including α-Si3N4,Ca CO3 and Ca(CH3COO)2,and Eu2O3.Compared with the prevailing conventional methods,an inexpensive and simple method under atmospheric pressure with a relative short reaction time is achieved.The reaction process is researched and the method is optimized to obtain a high purity of Ca2Si5N8:Eu2+ phosphors.The phosphors exhibit red emission under ultra violet(UV)radiation.The phosphors show a broad emission band peaking at 592 nm and the excitation spectra between 250 nm and 550 nm.The broad band of excitation spectra implies the promising application in UV ray based red light-emitting diode(LED).These results indicate a promising prospect for this efficient and economic route in preparing Ca2Si5N8:Eu2+ phosphors for LED applications.Sr2-x Cax Si5N8:Eu2+ phosphors were synthesized in a facile way by high temperature soild state method by using the raw materials of Ca CO3,Ca(CH3COO)2,Sr CO3 and Sr(CH3COO)2.The emission color of phosphors can be adjusted as changing the type and content of the doped ions.Compared to the Ca2Si5N8 and Sr2Si5N8 phosphors,the luminescence of Sr2-x Cax Si5N8 phosphors had an obvious red shift with the same mole rato of Eu doped from 609 nm to 623 nm.With the concentration of the Eu doped in Sr2-x Cax Si5N8 phosphors,the phenomenon of the red shift adjusted by the subsititution of Ca ions was not obvious anymore.When the concentration of the Eu was 25at%,the emission of the Sr2-x Cax Si5N8 phosphors can peak at 667 nm.