CW Amplified Upconverted Emission in Blended NaYF₄:Yb³+, Tm³+ and NaYF₄:Yb³+, Er³+ Supraparticles

Upconverting nanoparticles (UCNPs) have gained significant interest due to their ability to emit UV or visible light when excited in the near infrared (NIR) [1]. They exhibit long luminescence lifetimes and narrow spectroscopic features, which make them promising for applications such as colour multiplexing in biological media and security coding. While UCNPs have low absorption due to their size relative to the light's wavelength, micro-assemblies of UCNPs called supraparticles (SPs) address this limitation. SPs exhibit optical resonances and facilitate amplified stimulated emission (ASE) [2], making them a promising option for achieving intense emission.