BaSi 2 O 2 N 2 :Eu 2+Performance Study And First-principles Calculation Of A Series Of Phosphors

As a new solid state lighting source, white lighting emitting diode (WLED for short) is considered as the forth generation green lighting products. In the past decades, silicon based (oxy)nitride phosphors drawn our attention because it can be efficiently excited by ultraviolet-visible light with high luminescence efficiency, high thermal stability,high designability and barely no pollution. It's regarded as one of the best phosphors for LED application followed by YAG:Ce3+ and silicate phosphors.Among them, BaSi2O2N2:Eu2+ (oxy)nitride green phosphor promose well for its low preparation cost, pure luminescence light and high thermal stability.Literature review shows that: Although BaSi2O2N2:Eu3+has advantages in its luminescence properties, the excitation spectra needs broadening, the luminescence efficiency needs to be improved further and the relationship between its crystal structure and optical properties needs to be built. Hence,this paper synthesized BaSi2O2N2:Eu2+?Sr2+ doped BaSi2O2N2:Eu2+ and Mn2+ doped phosphors and studied the influence of these factors on the optical properties of BaSi2O2N2:Eu2+. Moreover,first-principles calculation based Density Function Theory (DFT) is conducted to study the relationship between crystal structure, electronic structure and optical properties on three kinds of BaSi2O2N2:Eu2+ phosphors above. The major researches are shown as below:(?)Properties study and first-principles calculation on BaSi2O2N2:Eu2+(1) BaSi2O2N2:Eu2+ with various Eu2+ doping concentrations are synthesized.Research results show that the emission intensity increases and then decreases with increasing Eu2+ doping concantratons. When Eu2+ content is 0.05, the emission intensity reaches the maximum. The quenching concentration is 0.05.(2) First-principles calculation results show that both Ba2+ and Eu2+ have contribution to the absorption of BaSi2O2N2:Eu2+, especially Ba2+ exhibits long-wavelength absorption. When Eu2+ doping content increases, the crystal lattice contracts, Eu-N bond length shortens and the crstal field strength increases. All these factors leads to the decline of the energy differences between the ground state and the excited state and the emission color redden.(?)Properties study and first-principles calculation on Sr2+ doped BaSi2O2N2:Eu2+(1) BaSi2O2N2:Eu2+ with various Sr2+ doping concentrations are synthesized.Research results show that the emission intensity at 497nm decreases gradually with increasing Sr2+ doping content. When the Sr2+ doping content is 0.05, a new emission peak at around 566nm appears and the new emission peak may orginate from the solid solute (Sr/Eu)Si2O2N2 in the sample.(2) Simulation results indicate that the lattice parameters decrease and the volume of the crystal contracts when Sr2+ is doped into the crystal. The conduction band in the range of 1.1eV-4.9eV is mainly consisted of united d orbit of Ba2+,Sr2+and Eu2+,as well as 3p state of Si4+. The doping of Sr2+ decrease the energy difference between the lowest Eu2+ 5d state and 4fstate, which reddens the emission color.(?)Properties study and first-principles calculation on Mn2+ doped BaSi2O2N2:Eu2+(1) BaSi2O2N2:Eu2+ with various Mn2+ doping concentrations are synthesized.Research results show that the emission intensity can be enhanced by codoping Mn2+.When Mn2+ doping content is 0.01, the emission intensity reaches the maximum with the emission intensity increased by 55%.(2) Simulation results indicate that the crystal lattice deformed and the Eu-N bond decreases when Mn2+ is doped into the crystal. All the factors above increases the crystal field intensity around Eu2+. The absorption peak moves to longer wavelength band, which favors the absorption of blue light by InGaN chips.