Lattice perturbation by optically inert Sc 3+ grants NaGdF 4 upconversion nanocrystals giant emission and excitation-gated thermal response

:Er upconversion (by up to 146-fold) and exhibits an excitation-gated thermal response: emission is temperature-invariant at 980 nm but shows a green-to-red shift at 1550 nm, thus establishing a versatile platform for programmable luminescent materials.