The use of energy looping between Tm 3+ and Er 3+ ions to obtain an intense upconversion under the 1208 nm radiation and its use in temperature sensing

Core@shell nanoparticles doped with Tm 3+ and Er 3+ ions exhibit intense temperature-dependent photon upconversion when subjected to 1208 nm laser excitation. The mechanism behind this observed emission is elucidated, unveiling its intricate nature.