  Photon avalanching nanoparticles (ANPs) exhibit extremely nonlinear
upconverted emission valuable for sub-diffraction imaging, nanoscale sensing,
and optical computing. Avalanching has been demonstrated with Tm3+, Nd3+ or
Pr3+-doped nanocrystals, but their emission is limited to 600 and 800 nm,
restricting applications. Here, we utilize Gd3+-assisted energy migration to
tune the emission wavelengths of Tm3+-sensitized ANPs and generate highly
nonlinear emission of Eu3+, Tb3+, Ho3+, and Er3+ ions. The upconversion
intensities of these spectrally discrete ANPs scale with the nonlinearity
factor s = 10-17 under 1064 nm excitation at power densities as low as 6
kW/cm2. This strategy for imprinting avalanche behavior on remote emitters can
be extended to fluorophores adjacent to ANPs, as we demonstrate with
CdS/CdSe/CdS core/shell/shell quantum dots. ANPs with rationally designed
energy transfer networks provide the means to transform conventional linear
emitters into a highly nonlinear ones, expanding the use of photon avalanching
in biological, chemical, and photonic applications.
