Time-Tuned Photon Avalanche Upconversion in Nanoparticles for Optical Logic and Multidimensional Data Encoding

The increasing demand for ultrafast data processing and high-density information storage necessitates photonic platforms capable of optical logic operations and multidimensional data encoding. However, most optical materials exhibit insufficient nonlinear absorption and limited tunability, preventing threshold-controlled switching for deterministic logic. Lanthanide-doped upconversion nanoparticles circumvent these limitations through discrete ladder-type manifolds, energy transfer, and strong nonlinear excitation pathways. Here, we report time-tuned photon avalanche upconversion in NaYF4:Yb3+/Pr3+(15/0.5%)@NaYF4 nanoparticles under 852 nm pulsed excitation as a reconfigurable platform for logic and encoding. By independently modulating the pulse width and frequency, we establish orthogonal control over avalanche kinetics and branching ratios. Long pulse widths promote excited-state population buildup, enhancing cross-relaxation-assisted feeding into higher-lying Pr3+ states and producing dominant blue emission. Conversely, high repetition frequencies reduce ground-state recovery, increase Yb3+ sensitizer recycling, and drive saturation-like regimes favoring red channels. Rate equation simulations corroborate the observed transitions in the emission color, temporal profile, and threshold behavior. Reversible color switching was demonstrated in both the photon avalanche and saturation regimes with tunable blue-to-red emission ratios. These dynamics enable optical logic gates and multidimensional encoding leveraging emission wavelength, lifetime, and temporal switching, establishing a framework for high-speed photonic computing and scalable high-capacity data encoding.