KLn(MoO) micro/nanocrystals (Ln = La-Lu, Y): systematic hydrothermal crystallization, structure, and the performance of doped Eu for optical thermometry.

Systematic crystallization of KLn(MoO) double molybdate micro/nanocrystals was achieved in this work for the family of lanthanide elements (excluding Pm) and Y hydrothermal reaction under the optimized conditions of pH = 7, Mo/Ln molar ratio = 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 KLaEu(MoO) (KLM:Eu) and KYEu(MoO) (KYM:Eu) red phosphors, and detailed spectral analysis found that the layered structure of orthorhombic KYM allows Eu to have a high quenching content of ∼70 at% ( = 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 D and D energy levels of Eu.