Luminescence color tuning and energy transfer properties in (Sr,Ba)2LaGaO5:Bi3+,Eu3+ solid solution phosphors: realization of single-phased white emission for WLEDs
Recently, controllable luminescence tuning and single-phased white light emitting have been extensively studied to improve the luminescence performances of phosphors for white light-emitting diodes (WLEDs). In this work, the controllable photoluminescence tuning from bluish-green to red region was successfully achieved in Bi3+, Eu3+-codoped Sr2-yBayLaGaO5 solid solutions, combining the effects of crystallographic site engineering and energy transfer. The phase composition and structural variation of the designed phosphors were thoroughly analyzed through X-ray powder diffraction (XRD) and Rietveld refinement. The effects of cation substitutions on the photoluminescence properties were investigated in detail and corresponding mechanism was proposed. The regular red-shift of Sr2-yBayLaGaO5:0.02Bi3+ in bluish-green region could be observed when Sr2+ was substituted by Ba2+, which is attributed to crystal field splitting and nephelauxetic effect. The red-shift emission of Ba2LaGaO5:0.02Bi3+ phosphor with gradually increasing excitation wavelength reveals that Bi3+ ions occupy different cation sites to form multiple luminescent centers. Besides, the efficient energy transfer was designed and successfully realized in Sr2-yBayLaGaO5:0.02Bi3+, zEu3+ (y = 0-2.0; z = 0-0.20) samples. The energy transfer efficiency can reach up to 88%, 91% and 77% at z = 0.20 for y = 0, 1.0 and 2.0, respectively. Moreover, the thermal quenching behaviors of the studied phosphors reveals that the codoping of Eu3+ could efficiently improve the thermal stability of Sr2LaGaO5:0.02Bi3+ phosphor. Finally, the WLED devices were fabricated by composing of 370 nm UV chips and single-phased Sr2-yBayLaGaO5:0.02Bi3+, 0.05Eu3+ (y = 0, 1.0, 2.0) phosphors. The as-fabricated devices presented relatively excellent EL performances, the color coordinates of which all locate in the warm white light region. These results indicate the as-prepared Sr2-yBayLaGaO5:Bi3+, Eu3+ phosphors can be potential candidates for color tuning and efficient single-phased white emission in UV-based WLED lighting applications.