Effects of co-activator species and transition metal ions doping on structure and fluorescence properties of strontium aluminate phosphors

Abstract

The phosphors of SrAl₂O₄: Eu²⁺, RE³⁺ (RE = Dy³⁺, Tb³⁺, Ho³⁺, La³⁺, Nd³⁺, Y³⁺, Tm³⁺, Er³⁺) and SrAl₂O₄: Eu²⁺, Dy³⁺, M²⁺ (M = Mn²⁺, Ni²⁺, Mg²⁺, Cu²⁺, Zn²⁺) were synthesized by co-precipitation combined hydrothermal method, and analyzed by X-ray diffraction (XRD), fluorescence spectrometer and SEM. XRD patterns illustrated that the synthesized products all were the mixed crystal phase of SrAl₂O₄ and Sr₄Al₁₄O₂₅. The diffraction peaks shapes of phosphors SrAl₂O₄: Eu²⁺, RE³⁺ (RE = Tb³⁺, Ho³⁺, Y³⁺) were almost unchanged contrast to the marked changes of phosphors SrAl₂O₄: Eu²⁺, RE³⁺ (RE = Tm³⁺, Er³⁺, Nd³⁺, La³⁺), which showed co-activator species had a great impact on the crystal field around the emission center (Eu²⁺). Besides, the peak positions of SrAl₂O₄: Eu²⁺, Dy³⁺, M²⁺ (M = Mn²⁺, Ni²⁺, Mg²⁺, Cu²⁺, Zn²⁺) were unaltered after doping, while the peak intensity of crystal phase Sr₄Al₁₄O₂₅ was enhanced after doped by cations (Mn²⁺, Ni²⁺, Cu²⁺, Zn²⁺), which indicated the doping of transition metal ions would cause the crystal phase transition. The fluorescence analysis results indicated that the luminescent intensity were reduced after being doped by co-activator ions (Dy³⁺, Tb³⁺, Ho³⁺, La³⁺, Nd³⁺, Y³⁺), but enhanced when doped by co-activator ions (Tm³⁺, Er³⁺), and the final emission wavelength and intensity sequence were as follows: $\lambda$_Nd < $\lambda$_La < $\lambda$_Er < $\lambda$_Y < $\lambda$_Tm < $\lambda$_Tb < $\lambda$_Ho < $\lambda$_Dy, I_Nd < I_Dy < I_Y < I_Tb < I_Ho < I_La < I_Tm < I_Er. Instead, the fluorescence emission intensity decreased with the increment of the doping concentration of transition metal ions, which perhaps because the transition metal ions doping under the optimal concentration of co-activator could reduce the luminescence intensity of products due to the concentration quenching. The crystal particles of SrAl₂O₄: Eu²⁺, Dy³⁺ presented regular hexagon flake-like morphology with a width of ~ 500 nm and a thickness of ~ 70 nm. The title products could be applied in the safety indicators, emergency lighting danger signals, automobiles, solar cells, etc.