Multiband emission from single ?-NaYF4(Yb,Er) nanoparticles at high excitation power densities and comparison to ensemble studies

Abstract Ensemble and single particle studies of the excitation power density ( P )-dependent upconversion luminescence (UCL) core core-shell ?-NaYF 4 :Yb,Er nanoparticles (UCNPs) doped with 20% Yb 3+ 1% or 3% Er performed over a regime 6 orders magnitude reveal an increasing contribution emission from high energy levels at > 1 kW/cm 2 . This changes overall color initially green yellow to white. While red dominate in ensemble measurements < , population higher by multiphotonic processes results multitude bands ultraviolet/visible/near infrared (UV/vis/NIR) accompanied decreased luminescence. Based upon thorough analysis P-dependence UCL, activated were grouped assigned 2–3, 3–4, photonic involving transfer (ET), excited-state absorption (ESA), cross-relaxation (CR), back (BET), non-radiative relaxation (nRP). underlines -tunability UCNP brightness highlights potential -dependent for mechanistic required manifest pathways different levels.