Fig. 1. Principle of nanoscale RETA optical writing on a GO-conjugated UCNP nanocomposite.

(A) The writing beam induces GO reduction through RET of high-energy quanta from UCNPs, while the inhibition beam inhibits GO reduction through suppression of high-energy quantum generation in UCNPs. (B) The experimental setup of a dual-beam super-resolution configuration that enables writing of subdiffraction features on the nanocomposite. (C) Simulated intensity distribution of the 980-nm writing beam with a Gaussian shape (writing), the 808-nm inhibition beam with a doughnut shape (inhibition), and their spatial overlap (writing + inhibition) along the radial direction in the focal plane. (D) Simulated intensity distribution on the nanocomposite irradiated with the dual-beam super-resolution configuration (writing + inhibition) with a writing beam intensity of 0.13 MW cm⁻² and an inhibition beam intensity of 11.25 MW cm⁻². (E) Simulated intensity profile along the dashed line in (D). (F) The 450-nm upconversion luminescence emission intensity from the nanocomposite after irradiation with the dual-beam super-resolution configuration (writing + inhibition). (G) Intensity profile along the dashed line in (F). a.u., arbitrary units.