Bluish-green emission of novel BaAl2Ge2O8:Eu2+ phosphors under near-ultraviolet excitation

Abstract

A new class of phosphor samples, denoted as Ba1–xAl2Ge2O8:xEu2+ (BAGO:xEu2+) was synthesized using Pechini-type sol–gel technique and subsequently underwent thermal reduction in CO atmosphere. The morphology and structural characteristics of both the BAGO host lattice and the Eu2+ ions activated BAGO phosphors were investigated through field-emission scanning electron microscopy and X-ray diffractometry analyses, respectively. The BAGO host lattice has micro-sized particles and the Rietveld refinement reveals the presence of a monoclinic crystal phase, characterized by the space group I12/c1 (No. 15). Introducing Eu2+ ions into Ba2+ sites under CO conditions reduces the particle size, switching from micrometer to nanoscale. Within the near-ultraviolet spectrum (353 nm), the BAGO:xEu2+ phosphors exhibit a broadband blueish-green photoluminescence (PL) emission characterized by a peak band at 492 nm. This phenomenon is attributed to the 4f6 5d1 → 4f7 electronic transition. The BAGO:0.02Eu2+ phosphor sample exhibits the strongest bluish-green PL emission, and a comprehensive description of the concentration quenching mechanism between Eu2+ ions is revealed. Additionally, the thermal stability of the optimized BAGO:0.02Eu2+ phosphor was investigated, and its activation energy was estimated. Therefore, the synthesized bluish-green BAGO:0.02Eu2+ phosphor holds the promise of being a novel and promising candidate for utilization in white-light-emitting diode applications.