Effect of synthesis method on the structural and optical properties of blue-excitable La_2−xPr_x(MoO₄)₃ phosphors

Structural, optical and photoluminescent properties of La_2−xPr_x(MoO₄)₃ phosphors with different doping concentrations of Pr³⁺, synthesized by conventional solid-state and solution combustion routes were studied. X-ray diffraction studies of compounds synthesized through conventional solid-state ceramic route confirm that all samples crystallized in monoclinic La₂(MoO₄)₃ structure with c2/c space group, while combustion synthesized compounds show the existence of two different crystal environments. Analysis of UV–visible diffuse reflectance spectra (DRS) shows characteristics of absorption bands in blue and red regions for Pr³⁺ substituted La₂(MoO₄)₃ samples, synthesized by both methods. The calculated band gap from the DR spectrum showed an inverse dependence with Pr³⁺ doping concentration for solid-state synthesized La_2−xPr_x(MoO₄)₃ samples, while for combustion synthesized La_2−xPr_x(MoO₄)₃ compounds the variation of band gap with concentration is not monotonous. The photoluminescence emission spectrum of blue excited La_2−xPr_x(MoO₄)₃ phosphors synthesized by both routes showed similar multicoloured emission bands. Maximum emission intensity was observed for Pr³⁺ concentration of x = 0.05 in both synthesis methods. The exchange interaction between nearest activator ions leads to concentration quenching of luminescence for solid-state synthesized La_2−xPr_x(MoO₄)₃ compounds and dipole–dipole interaction for combustion synthesized La_2−xPr_x(MoO₄)₃ compounds. The average emission colour of the blue excited La_2−xPr_x(MoO₄)₃ phosphors lies in the yellow–orange region. The CCT values lie in the warm light region and the luminescence lifetime of 8 µs for red emission peak showed promising applications requiring fast switching response.