KLn(MoO4)2 micro/nanocrystals (Ln = La–Lu, Y): systematic hydrothermal crystallization, structure, and the performance of doped Eu3+ for optical thermometry

Abstract

Systematic crystallization of KLn(MoO₄)₂ double molybdate micro/nanocrystals was achieved in this work for the family of lanthanide elements (excluding Pm) and Y via hydrothermal reaction under the optimized conditions of pH = 7, Mo/Ln molar ratio R = 5 and 200 °C, with which the intrinsic influence of lanthanide contraction on phase preference, crystallite morphology (size/shape) and crystal structure was clearly revealed. Extended synthesis also produced KLa_1−xEu_x(MoO₄)₂ (KLM:xEu) and KY_1−yEu_y(MoO₄)₂ (KYM:yEu) red phosphors, and detailed spectral analysis found that the layered structure of orthorhombic KYM allows Eu³⁺ to have a high quenching content of ∼70 at% (y = 0.7) and higher quantum efficiency and thermal stability of luminescence. Application also indicated that the KYM:0.7Eu optimal phosphor has the potential for optical temperature sensing with the thermally coupled ⁵D₀ and ⁵D₁ energy levels of Eu³⁺.