Highly efficient upconversion luminescence in narrow-bandgap Y₂Mo₄O₁₅

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Lanthanide-doped upconversion (UC) materials convert low-energy excitation to high-energy emission.
• Efficient UC luminescence (UCL) was previously thought to require wide bandgap materials.
• Y2Mo4O15:Yb3+/Tm3+ microcrystals are narrowband materials with unique optical properties.

Purpose of the Study:

• To investigate upconversion luminescence in narrowband Y2Mo4O15:Yb3+/Tm3+ microcrystals.
• To challenge the notion that efficient UCL is exclusive to wide bandgap materials.
• To explore the potential of these microcrystals in anti-counterfeiting and information encryption.

Main Methods:

• Experimental synthesis and characterization of Y2Mo4O15:Yb3+/Tm3+ microcrystals.
• Spectroscopic analysis of upconversion luminescence.
• Theoretical calculations to understand the underlying optical mechanisms.
• Comparison of UCL intensity with commercial upconversion phosphors.

Main Results:

• Highly efficient UC emission was observed in narrowband Y2Mo4O15:Yb3+/Tm3+ microcrystals.
• The emission intensity significantly surpasses that of commercial NaYF4:Yb3+,Er3+ and NaYF4:Yb3+,Tm3+ phosphors.
• The vanishing of four- and five-photon UC emission bands was attributed to strong host-dopant interactions.

Conclusions:

• Narrowband Y2Mo4O15:Yb3+/Tm3+ microcrystals exhibit superior UCL efficiency, contrary to prior beliefs.
• The observed phenomenon is linked to the interaction between the Y2Mo4O15 bandgap and Tm3+ energy levels.
• These microcrystals are promising for advanced anti-counterfeiting and information encryption technologies.