The Study Of Crystal Structure And Luminescence Properties Of CaAlSiN₃:Ce³⁺ Nitrides

In this paper,Ca_1-xSiAlN₃:xCe³⁺(denoted as CASN:Ce³⁺@CeB₆ and CASN:Ce³⁺@CeO₂)series nitrides yellow phosphor have been synthesized by direct-nitriding method.CeB₆,CeO₂ and EuB₆ was used as activators.The morphologies,crystal phases,element distribution,luminescence properties and thermal stability were discussed in detail.A series of CeB₆-doped and CeO₂-doped Ca_1-xSiAlN₃:xCe³⁺(denoted as CASN:Ce³⁺@CeB₆ and CASN:Ce³⁺@CeO₂ respectively)were synthesized.Ca_1-xSi alloy was used as raw material.With an increase of the concentration of CeB₆,the unit cell volume of CASN:Ce³⁺@CeB₆ slightly increases,which leads to a change of microstructure around Ce³⁺.CASN:Ce³⁺@CeB₆efficiently emits yellow-orange light with a maximum emission intensity at around 550 nm for the content x of 0.01(being in comparable situation,CASN:Ce³⁺@CeO₂ is x=0.04)when excited at 460 nm.The red emission component of Ce³⁺in CASN:Ce³⁺@CeB₆ was much stronger.This is ascribed to energy transfer of intra-Ce³⁺(within one Ce³⁺ion)and inter-Ce³⁺(between Ce³⁺and Ce³⁺ions).In addition,the replacements of N^3-?1.32?for CN=4?and O^2-?1.24?for CN=4?by B^2-?1.40?for CN=4?,which can lead to a marked expansion of the host lattice and a decrease of the oxidation of samples,are also responsible for the increase of red emission component.Furthermore,CASN:Ce³⁺@CeB₆ phosphor has an excellent thermal stability because of the partial substitution of Ce-O?Ce-N?bonds by more covalent Ce-B.And the optimum dopant concentration is x=0.01 for CASN:Ce³⁺@CeB₆,is smaller than that of CASN:Ce³⁺@CeO₂,which lead to a excellent thermal stability of CASN:Ce³⁺@CeB₆.The doping Ce³⁺ions are preferable to substitute Ca²⁺sites in CASN:Ce³⁺,which lead to the presentence of charge compensating defects in the lattice.Charge compensated ion Li⁺was introduced to sample to balance the charge difference,and thus,two Ca²⁺was replaced by[CeLi]⁴⁺.The crystallinity of the CASN:Ce³⁺@CeB₆ phosphors with Li⁺doped(denoted as Ca_1-2xLi_xAl SiN₃:xCe³⁺)are better than that of CASN:Ce³⁺@CeB₆ without Li⁺doped(denoted as Ca_1-xAlSiN₃:xCe³⁺).The photoluminescence spectra intensity of Ca_1-2xLi_xAlSiN₃:xCe³⁺phosphor is about 1.7 times than that of Ca_1-xAlSiN₃:xCe³⁺phosphorwhenx=0.04.Furthermore,Ca_1-2xLi_xAl SiN₃:xCe³⁺phosphor has an excellent thermal stability.This is ascribed that charge compensation is necessary to change the coordination conditions for Ce³⁺,balance out the defects to achieve the enhancement of Ce³⁺emission.The red emission component of Ce³⁺in CASN:Ce³⁺@CeB₆using Ca_1-xSi alloy as raw material is much more than Ca_1-xAlSiN₃:xCe³⁺phosphor.The CASN:0.04Ce³⁺,yEu²⁺phosphors were prepared by a direct-nitriding method.The half peak width of CASN:0.04Ce³⁺,0.01Eu²⁺phosphor is 125 nm,which is much wider than CASN:0.04Ce³⁺?the half peak width is 55 nm?and CASN:Ce³⁺@CeB₆?the half peak width is 100nm?using Ca_1-xSi alloy as raw material.In particular,the emission peak wavelength of Ce³⁺-Eu²⁺doped CASN:0.04Ce³⁺,yEu²⁺shifts to long wavelength with increasing of Eu²⁺.Tthe yellow light from Ce³⁺decrease rapidly,well the red light from Eu²⁺enhance effectively due to the energy transfer between Ce³⁺and Eu²⁺.A small amount of EuB₆ can be added to the CASN:0.04Ce³⁺phosphor to improve the color performance against actual conditions.As the result,the outstanding luminescent properties of CASN:Ce³⁺@CeB₆ phosphor make it practical to use in the single phosphor-coated high-color-rendering powerwhite LED.