Thermal loading induced near-infrared broadband upconversion emission of Sm3+-doped β-NaYbF4 nano-phosphors

► Sm3+ doped β-NaYbF4 nano-phosphors were synthesized by non-closed hydrothermal synthetic processing at 98 °C. ► Novel green, red, and near-infrared broadband upconversion emissions of Sm3+ are observed under 980 nm excitation. ► Half-width of 873 nm emission band is broadened nearly two-fold through the annealing treatment for nano-phosphors. ► Cooperative sensitization and phonon-assisted energy transfer process by the thermal loading mechanisms is discussed.