Highly sensitive Boltzmann thermometry by double-layered Bi ₂ SiO ₅ :Yb ³⁺ ,Tm ³⁺ @SiO ₂ hollow nanoparticles with exceptional thermometric performances and biocompatibility are demonstrated.

The energy transfer process between Tb³⁺ and Eu³⁺ ions in water-dispersible CaF₂ nanocrystals prepared using a simple process is reported. Fine colour control and long excited state lifetimes make the nanosystem suitable for biosensing applications.

In the field of novel applications involving upconverting processes, the determination of new strategies for realizing emission-tunable nanomaterials is a challenge. In this work the design of Y³⁺ and Er³⁺ codoped bismuth oxide-based upconverting nanoparticles is presented, evidencing that the active role of the matrix allows for the emission selectivity with chromaticity control. The bandgap of the bismuth oxide-based host can be manipulated in the range of 0.65 eV, consequently leading to upconversion emission color tunability from red to yellow-greenish. The resulting fine control of the nanoparticle chromaticity through accurate host bandgap engineering reveals a novel concept for the development of a new generation of upconverting nanophosphors.