Broad color tuning of Bi3+/Eu3+-doped (Ba,Sr)3Sc4O9 solid solution compounds via crystal field modulation and energy transfer

Abstract

Controllable luminescence tuning can modify and improve the luminescence performances of phosphor materials and thus promote their application in white light emitting diodes (W-LEDs). Usually, crystal field modulation by constructing solid solutions based on diverse composition substitutions and energy transfers are effective strategies for adjusting the luminescence properties of phosphors. Herein, we report a series of novel emission-tunable Ba_3−xSr_xSc₄O₉:yBi³⁺,zEu³⁺ (x = 0–3.0, y = 0–0.15, z = 0–0.30) solid solution phosphors synthesized via a high-temperature solid-state route. The XRD patterns and Rietveld refinements were utilized to confirm the phase purity and analyze the structural variation. Cation substitution-dependent color-tunable evolution as a function of Sr content in Bi³⁺-doped Ba_3−xSr_xSc₄O₉ was observed and investigated in detail. The regular emission red-shift located in the blue-green region with the increase of Sr content was attributed to the combined effect of the crystal field splitting. Due to the suitable optical band gap (5.50 eV), Bi³⁺ ions realized a highly efficient doping in the Sr₃Sc₄O₉ matrix. The as-prepared Sr₃Sc₄O₉:Bi³⁺ samples were efficiently excited by UV light, and the photoluminescence properties presented obvious preferential-occupation selected excitation phenomenon where the emission peaks had remarkable red-shifts along with increasing the excitation wavelength. In addition, luminescence tuning from green to orange was achieved by designing the energy transfer from Bi³⁺ to Eu³⁺ ions in the as-prepared Sr_2.97−zSc₄O₉:0.03Bi³⁺,zEu³⁺ samples and the corresponding mechanism was proposed. Moreover, the thermal stabilities of the studied phosphors were revealed. According to the distortion calculation of the Ba/Sr crystallographic occupation, the thermal stability is related to the lattice rigidity, which would become much stronger with the reduction of distortion. These results illustrate that the as-prepared Ba_3−xSr_xSc₄O₉:Bi³⁺,Eu³⁺ phosphors can be potential candidates for color-tunable phosphors applied in UV-pumped W-LEDs.