Optical Upconversion in Mononuclear Lanthanide Co-Crystal Assemblies.

Area of Science:

• Inorganic Chemistry
• Materials Science
• Luminescence

Background:

• Lanthanide ions exhibit unique photoluminescent properties.
• Upconversion luminescence (UCL) allows conversion of lower energy photons to higher energy photons.
• Yb³⁺ sensitization is a common strategy to enhance UCL in lanthanide systems.

Purpose of the Study:

• To develop novel co-crystal assembly systems for lanthanide upconversion luminescence.
• To investigate the effect of Yb³⁺ sensitization on Er³⁺ and Pr³⁺ upconversion.
• To elucidate the energy transfer mechanisms responsible for UCL.

Main Methods:

• Synthesis of discrete mononuclear Yb³⁺/Er³⁺ and Yb³⁺/Pr³⁺ co-crystal assemblies.
• Characterization of crystal structure and composition using single crystal X-ray diffraction.
• Photoluminescence spectroscopy under 980 nm excitation to study upconversion luminescence.

Main Results:

• Two co-crystal systems were successfully developed, achieving Er³⁺ and Pr³⁺ UCL via Yb³⁺ sensitization.
• The strongest UCL for both Er³⁺ and Pr³⁺ systems was observed at a Yb³⁺:Ln³⁺ molar ratio of 1:1.
• Energy transfer mechanisms were identified as energy transfer upconversion for Er³⁺ and a combination of energy transfer and cooperative sensitization upconversion for Pr³⁺.

Conclusions:

• The study demonstrates efficient Yb³⁺-sensitized upconversion luminescence in discrete lanthanide co-crystal assemblies.
• The findings highlight the importance of the Yb³⁺:Ln³⁺ molar ratio for optimizing UCL intensity.
• This work presents the first molecular-level demonstration of Pr³⁺ upconversion luminescence at room temperature, expanding the field of lanthanide luminescence.