Preparation And Luminescence Mechanism Of Al-doped Si₃N₄-Based Phosphor

The focus of this dissertation is put on?-Si₃N₄.Al-Eu co-doped?-Si₃N₄-based phosphor with great application potential in the solid state lighting field is fabricated by a facile direct nitridation method.The crystal structure and optical property of Al-doped?-Si₃N₄as well as the crystal structure,photoluminescence property and luminescence mechanism of Al-Eu co-doped?-Si₃N₄-based phosphor are investigated.The research results presented in this dissertation are shown as follows:The band structure of?-Si₃N₄ is sharply modulated by Al doping.Intermediate level within forbidden band introduced by interstitial Al make the bandgap of?-Si₃N₄decrease from 5.3 e V to 2.65 e V around,successfully making the bandgap of Al-doped?-Si₃N₄agree well with blue chip.Moreover,the bandgap of Al-doped?-Si₃N₄can be precisely regulated by tuning Al doping concentration.When Al doping concentration gradually ranges from Si:Al=1000:1 to 50:1,the bandgap of Al-doped?-Si₃N₄increases from 2.58 e V to 2.67,2.74,2.85 e V,which is ascribed to the increasing number of substitutional Al according to theoretical calculation results along with experimental results.The preferential orientation of Al-doped?-Si₃N₄microbelt is led by Al doping.In the case of low Al doping concentration,Al occupies at substitutional site and interstitial site in the?012?plane,intensifying the?012?plane and making?012?plane being stacking plane for sample SA200:1.By contrast,When Al doping concentration is on the rise,the existence of substitutional Al and interstitial Al in the?011?plane makes?011?plane denser,and consequently?011?plane becomes stable stacking plane for sample SA50:1.After successfully preparing Al-doped?-Si₃N₄with narrow bandgap,Al-Eu co-doped?-Si₃N₄-based phosphor is obtained by introducing rare-earth element Eu.The orange-red broad emission band whose peak is at 570 nm is observed when Al-Eu co-doped?-Si₃N₄-based phosphor is under 450 nm blue excitation.With Eu doping concentration increasing,there is no evidence of concentration quenching for Al-Eu co-doped?-Si₃N₄-based phosphor.The fact indicated by analysis of crystal structure that interstitial Eu in the?-Si₃N₄crystal lattice is surrounded by seven N atoms is a fundamental interpretation for this unusual phenomenon.The luminescence mechanism of Al-Eu co-doped?-Si₃N₄-based phosphor is unraveled through controlled experiments.Partial energy absorbed by Al doped?-Si₃N₄matrix is transferred to Eu²⁺under crystal field splitting influence in a nonradiative relaxation way,and eventually orange-red light originating from electron transition5d?4f is observed.The CCT of white warm LED fabricated by accompanying Al-Eu co-doped?-Si₃N₄-based phosphor and 450 nm blue chip can be controlled from 3000 K to 6000 K via changing phosphor concentration.