Coordination polymer templated engineering of YVO4:Eu submicron crystals and photoluminescence

Abstract

Submicron-sized cuboidal and octahedral (Y_0.95Eu_0.05)VO₄ crystals were selectively synthesized via hydrothermally reacting sodium vanadate with a (Y_0.95Eu_0.05)–tartrate coordination polymer (CP) precipitated at room temperature, where the CP compound was analyzed to be an amorphous mass having particle sizes of ∼300 nm and an approximate composition of (Y_0.95Eu_0.05)₂(C₄H₄O₆)₃·7.4H₂O. A series of well controlled experiments clearly revealed that a stoichiometric amount of VO₄³⁻ [VO₄³⁻/(Y_0.95Eu_0.05)³⁺ molar ratio R = 1.0] favors cuboidal crystals (∼300–500 nm), which are formed via tartrate-directed [001] stacking of ∼15 nm thick nanosquares exposed with high energy {001} facets, whereas superfluous VO₄³⁻ (R = 1.5 and 2.0) promotes the crystallization of octahedral crystals (∼600–800 nm) enclosed by low energy {101} facets. The acting mechanisms of reaction temperature (80–200 °C) and time (1–24 h) in structure and morphology evolution were discussed in detail. The octahedrons were also analyzed to have a ∼60% stronger 619 nm red emission and a larger (⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁) intensity ratio, though both the types of crystals have similar fluorescence lifetimes of ∼0.9 ms for their 619 nm main emissions.