LAUSR

Multi-functional lanthanides doped upconversion nanoparticles (UCNP) have spread its wings in the fields of flexible optoelectronics and biomedical applications. One of the ongoing challenges lies in achieving UCNP based nanocomposites which enable continuous wave (CW) laser action at ultralow-threshold. Here, gold sandwich UCNP nanocomposites {gold (Au1)-UCNP-gold (Au2)} capable of exhibiting lasing at ultralow-thresholds under CW excitation is demonstrated. The metastable energy-level characteristics of lanthanides is advantageous for creating population inversion. In particular, localised surface plasmon resonance based electromagnetic hotspots in the nanocomposites and the giant enhancement of scattering coefficient for the formation of coherent closed loops due to multiple scattering facilitates the process of stimulated emissions as confirmed by theoretical simulation. The nanocomposites are subjected to stretchable systems for enhancing lasing action (threshold ~0.06 kW/cm2) via light trapping effect. The applications on bioimaging of HeLa cells and antibacterial activity (photothermal therapy) are demonstrated using the newly designed Au1-UCNP-Au2 nanocomposites.