Upconversion Nanoparticle Imaging Simulator

Lanthanide-doped upconversion nanoparticles (UCNPs) do something ordinary fluorophores cannot: absorb two dim near-infrared photons and emit one bright visible photon, via energy-transfer upconversion between a Yb³⁺ sensitizer and an Er³⁺ activator inside a NaYF₄ nanocrystal lattice. This simulator solves the steady-state sensitizer/activator rate-balance equations live as you tune pump power, tissue depth and Yb:Er doping, driving a 3D cluster of glowing nanocrystals buried in a tissue slab. Watch the measured power-law exponent slide from the signature two-photon value of n≈2 down toward n≈1 as the sensitizer population saturates, and see how green and red emission survive re-emerging through tissue differently — the reason near-infrared-excited, deep-tissue-penetrating UCNP probes are used for imaging and theranostics beyond what surface fluorophores can reach.