The impact of nanocrystals size on luminescent properties and thermometry capabilities of Cr, Nd doped nanophosphors

Transition metal d-f emission based thermometry has recently proven to be an order of magnitude more sensitive than thermometers based on conventional f-f transitions in rare-earth ions. Little is known however about the susceptibility of these materials to nanoscale parameters, such as size or surface-to-volume ratio. Here we study the impact of nanocrystallite size on luminescent properties as well thermometry capabilities of CrNd co-doped LiLaP4O12 phosphors. In particular, we show that absolute emission intensity decreases (∼ 0.81%/nm), emission band position blue shifts (Δl ∼ −0.066 nmwave length/nmgrain size), temperature sensing range narrows (from 300 to 600 K at 240 nm down to 300-420 K at 20 nm), temperature sensitivity rises up (from 1%/K to ∼5%/K) and temperature resolution drops (from ∼0.3 °C down to 0.05 °C) gradually, when the size of NCs decreases from 240 down to 20 nm, respectively. As a consequence, proper design of host and dopants, enables finding optimal materials for many thermometry applications.