Crystal and Electronic Structures, Photoluminescence Properties of Eu2+-Doped Novel Oxynitride Ba4Si6O16-3x/2Nx

Yuanqiang Li,Takashi Takeda,Rong-Jun Xie,Yuan Fang,Lihong Liu,Naoto Hirosaki,Xiaoyun Li

doi:10.3390/ma3031692

Yuanqiang Li, Takashi Takeda + Show 5 more

Open Access

https://doi.org/10.3390/ma3031692

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Abstract

The crystal structure and the photoluminescence properties of novel green Ba4-yEuySi6O16-3x/2Nx phosphors were investigated. The electronic structures of the Ba4Si6O16 host were calculated by first principles pseudopotential method based on density functional theory. The results reveal that the top of the valence bands are dominated by O-2p states hybridized with Ba-6s and Si-3p states, while the conduction bands are mainly determined by Ba-6s states for the host, which is an insulator with a direct energy gap of 4.6 eV at Γ. A small amount of nitrogen can be incorporated into the host to replace oxygen and forms Ba4-yEuySi6O16-3x/2Nx solid solutions crystallized in a monoclinic (space group P21/c, Z = 2) having the lattice parameters a = 12.4663(5) Å, b = 4.6829(2) Å, c = 13.9236(6) Å, and β = 93.61(1)°, with a maximum solubility of nitrogen at about x = 0.1. Ba4Si6O16-3x/2Nx:Eu2+ exhibits efficient green emission centered at 515–525 nm varying with the Eu2+ concentration when excited under UV to 400 nm. Furthermore, the incorporation of nitrogen can slightly enhance the photoluminescence intensity. Excitation in the UV-blue spectral range (λexc = 375 nm), the absorption and quantum efficiency of Ba4-yEuySi6O16-3x/2Nx (x = 0.1, y = 0.2) reach about 80% and 46%, respectively. Through further improvement of the thermal stability, novel green phosphor of Ba4-yEuySi6O16-3x/2Nx is promising for application in white UV-LEDs.

Highlights

In the exploration of novel phosphors for applications in white LED lighting, several oxynitride based phosphors with improved properties have been created by partial cross-substitution ofSi-N for Al-O in the oxide based host lattices, like alkaline earth aluminates of MAl2O4:Eu2+(M = Ca, Sr, Ba) [1] and alkaline earth aluminosilicates, viz., Sr2Al2SiO7:Eu2+ [2] andSr3Al10SiO20:Eu2+ [3,4]
The density of states (DOS) and band structure calculation for Ba4Si6O16 were performed by first principles method using pseudopotentials and a plane wave basis set [18] within the density functional theory (DFT) performed by VASP package [19,20,21]
It can be seen that the valence band is mainly composed of the valence electrons of Ba-6s, Si-3s3p, and O-2p states with a bandwidth of about 9.5 eV

Summary

Introduction

In the exploration of novel phosphors for applications in white LED lighting, several oxynitride based phosphors with improved properties have been created by partial cross-substitution of. It is highly interesting to know whether or not a single nitrogen can be incorporated into the oxide based lattices occupied on the oxygen sites, which could be more flexible than the cross-substitution of Si-N Æ Al-O and increase the possibility of inventing novel oxynitride phosphor materials to meet the requirements of the development of white LEDs. The luminescence properties of rare-earth doped alkaline-earth silicates have been widely investigated [6,7,8,9,10,11,12,13,14,15,16]. For a better understanding of the photoluminescence properties, firstly we calculated the electronic structures of the host lattice of Ba4Si6O16 by first principles method, we characterized the crystal structure, photoluminescence properties, and thermal stability of Eu2+-doped Ba4Si6O16-3x/2Nx

Computational Details

Synthetic approaches

Characterization

Electronic structures of the Ba4Si6O16 host

Photoluminescence properties

Conclusions