Orthorhombic (NH₄,Li)Eu(MoO₄)₂ Solid Solution: Crystal Structure and Red-Emitting Photoluminescence

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Rare-earth molybdates are known for their luminescent properties.
• Polymorphism significantly influences material characteristics.
• Controlling crystal structure is key to optimizing phosphor performance.

Purpose of the Study:

• To synthesize and characterize a novel orthorhombic polymorph of (NH4,Li)Eu(MoO4)2.
• To investigate the photoluminescent properties of the new phase.
• To establish a facile synthesis route for new rare-earth molybdate structures.

Main Methods:

• One-pot low-temperature hydrothermal synthesis.
• Synchrotron X-ray powder diffraction.
• Rietveld refinement.
• Photoluminescence spectroscopy.

Main Results:

• A novel orthorhombic polymorph of (NH4,Li)Eu(MoO4)2 was successfully synthesized.
• The new phase crystallizes in the Pbcn space group, distinct from known polymorphs.
• Intense red photoluminescence with a dominant peak at ~615 nm was observed under UV excitation.
• Crystal-field splitting confirmed a noncentrosymmetric Eu3+ site.

Conclusions:

• Partial substitution of NH4 with Li enables the formation of a new orthorhombic polymorph.
• The hydrothermal method is effective for synthesizing unreported polymorphs under mild conditions.
• This work provides a new structure-property regime for rare-earth molybdate phosphors.