Preparation And Luminescence Properties Of Rare-earth Doped Several Nitride Based Long-wavelength-emitting Materials

In recent years,white light emitting diodes?WLED?have gradually replaced the tradiational lamps and became new generation lighting source because of their high bright light,long lifetime,high efficiency and environment friendly.As the main part of the WLED,phosphors with excellent luminescence properties are very important,especially long wavelength phosphros,which paly a major role in increasing the color rendering index and decreasing the crrelated color temperature?CCT?of the WLED.Recently,nitride based phosphors are the mainstream long wavelength phosphors because of their excellent luminescence properties,but there are some problems existing in nitride based phosphors.Therefore,in this work,we focused on improving thermal stability and adjusting the full width at half maximun?FWHM?of the emission band of nitride based phosphors as well as exploring novel nitride based long wavelength emitting phosphors.The main work is listed below:?1?A novel nitride based yellow light emitting phosphor of Li₂SrSi₂N₄:Ce³⁺has been successfully prepared through the gas press singtering.The luminescence properties and crystal structure of Li₂SrSi₂N₄:Ce³⁺has been investigated in detail.The results indicate that Li₂SrSi₂N₄is made up of two kinds of rings,which are formed by the SiN₄ tetrahedrons and connect with each other.Meanwhile,there are two kinds of Sr²⁺sites for Ce³⁺to occupy,which leads to broad emission band of Li₂SrSi₂N₄:Ce³⁺.The energy transfer between the two Ce³⁺luminescence centers has also been investigated in detail.Compared with commercial yellow light emitting phosphor of Y₃Al₅O₁₂:Ce³⁺,Li₂SrSi₂N₄:Ce³⁺not only has excellent thermal stability,but also have broad emission band,which covers the red emission region.?2?In the ternary phase diagram of M₃N₂-Si₃N₄-AlN?M=Ca,Sr and Ba?,we chosen Ca₅Si₂Al₂N₈ as object of study,which contains more alikaline earth elements.Therefore,Ca₅Si₂Al₂N₈ can be prepared under ordinary pressure and relative low temperature compared with commercial red phosphors of CaAlSiN₃:Eu²⁺.The relationship between the luminescence properties and crystal structure of Ca₅Si₂Al₂N₈:Eu²⁺has been investigated in detail.The results indicate that Ca₅Si₂Al₂N₈ contain edge-shared SiN₄ and AlN tetrahedrons,which form compact host lattice.Meanwhile,there are three kinds of Ca²⁺sites for Eu²⁺to occupy.Therefore,Ca₅Si₂Al₂N₈:Eu²⁺has broad excitation band,which contains NUV and blue even yellow region,and emits bright red light.The temperature-dependent luminescence spectra of samples indicate that Ca₅Si₂Al₂N₈:Eu²⁺has excellent thermal stability.?3?A novel Eu³⁺activated nitride based phosphors of Li₂SiN₂ and?-M₃B₂N₄?M=Ca,Sr?have been successfully prepared through the sample pressure sintering.The luminescence properties and crystal structure of samples have been investigated in detail.The results indicate that Eu³⁺activated nitride phosphors have charge transfer band of Eu³⁺-N^3-,which is dependent on the coordinated anion.In Eu³⁺activated?-Sr₃B₂N₄,the charge transfer band can reach 370 nm,which can be well excited by NUV-LED chips.Meanwhile,?-Sr₃B₂N₄:Eu³⁺can emit sharp red emission light,which is resulted from Eu³⁺⁵D₀-⁷F₂ spin-forbidden transitions.Therefore,we have realized the narrow band red emitting phosphor with broad excitation band in?-Sr₃B₂N₄:Eu³⁺.Furthermore,we found that the charge transfer band not only relies on coordinated anion,but also is affected by next nearest neaighbor cationic.So we can realize the narrow band red emitting phosphors,which can be excited by blue-LED chips.