The past decade has seen extensive developments in the field of upconversion nanotechnology, which has found applications in various fields. Different applications require different emission wavelengths from nanoparticles, and significant research has been undertaken to fine tune individual emission peaks in shorter wavelengths without much success. Recently, a novel class of upconversion nanoparticles with an orthorhombic crystal structure has been developed, which enables high concentrations of activator ions to be used without concentration quenching and also allows for the excellent tuning of shorter emission wavelengths.