Preparation And Properties Of Silicate Luminescent Materials For N-UV Excited White LED

Compared with traditional halogen lamp,incandescent lamp and other lighting tools,white LED possesses the advantages of high intensity,long operation life,energy saving and environment-friendly,white LED has become new generation of lighting source.Phosphor is an essential component of white LED,whose performance directly affects the luminous intensity and efficiency of white LED.At present,silicate luminescent materials have been widely studied because of their excellent physical and chemical stability and low cost.Many blue light emitting silicate luminescent materials have been found and applied,but yellow-emitting silicate luminescent materials are relatively few reported.In this paper,silicate is taken as the research object,and novel types of yellow-emitting silicate luminescent materials are developed by structure derivation.The specific experimental results are as follows:?1?Na₂HfSiO₅:Eu²⁺phosphor was successfully prepared by high temperature solid-state method.The crystal structure of Na₂HfSiO₅ and the luminescent properties of Eu²⁺doped phosphors were studied by means of structural refinement and spectral characterization.Na₂HfSiO₅ is composed of SiO₄tetrahedra and HfO₆ octahedra by sharing O^2-.There are four different Na⁺sites that can be occupied by Eu²⁺ions.Multiple sites lead to an asymmetric broad-band emission.The interaction of energy transfer between Eu²⁺was studied by the measurement of spectra and attenuation curve.The LED device with excellent performance can be obtained by using the prepared yellow powder,commercial blue phosphor,red phosphor and a n-UV chip.?2?Structure derivatization is an important method to explore novel phosphors.By substituting Zr of Na₄Zr₂Si₃O₁₂ compound with Hf,a new Eu²⁺-activated yellow luminescent material Na₄Hf₂Si₃O₁₂:Eu²⁺was designed and synthesized.This homologous substitution method provides us the idea for preparing new phosphors.Through the structure refinement,it is known that Na₄Hf₂Si₃O₁₂ belongs to the trigonal structure,and there are two different Na⁺environments.By introducing the activator Eu²⁺,the asymmetric yellow–emitting phosphor with half peak width of 126 nm was obtained.By testing its thermal stability,it is found that its luminous intensity changes linearly with temperature,and the phosphor can also be used as a temperature sensor.?3?In the process of exploring new yellow-emitting phosphor,a new blue light silicate luminescent material Na₂HfSi₂O₇:Eu²⁺was prepared.The well-known commercial blue phosphors was BaMgAl₁₀O₁₇:Eu²⁺(BAM:Eu²⁺),but the excitation ability of BAM:Eu²⁺in the near UV region is poor,which can not be well matched with the n-UV chips?380-420 nm?.However,Na₂HfSi₂O₇:Eu²⁺can be excited well in the region of 250-450 nm because of its high structural symmetry and tight multi-rings structure.The narrow band emission with a half peak width of 54 nm was ascribed to the two Na⁺sites with little difference.The LED device based on Na₂HfSi₂O₇:Eu²⁺,commercial green and red phosphors,and a n-UV chip have high color rendering index and low correlated color temperature,which proves that it is a candidate for WLED.