Structure Evolution and Up‐Conversion Studies of ZnX2O4:Er3+/Yb3+(X = Al3+, Ga3+, In3+) Nanoparticles

Abstract A series of ZnX 2 O 4 :Er 3+ /Yb 3+ (X = Al 3+ , Ga 3+ , In 3+ ) nanoparticles were obtained by using a modified Pechini technique. The crystal structure, morphology, and chemical composition of the engineered compounds were characterized in detail by means of X‐ray diffraction, Micro‐Raman spectroscopy, transmission electron microscopy (TEM) and selected area electron diffraction, and energy‐dispersive X‐ray spectroscopy. Particle sizes were estimated by using theoretical calculations (Scherrer and Rietveld methods) as well as experimental techniques [TEM and dynamic light scattering (DLS)] and were, furthermore, cross‐compared. The calculated average grain size, for dry powders, is in the range 20–45 nm. The hydrodynamic size was measured by using the DLS technique on nonmodified, surfactant‐free particles of the whole ZnX 2 O 4 series. The up‐conversion properties of the particles were discussed in detail. The low value of the green‐to‐red ratio points to a significant contribution of non‐radiative pathways, such as multiphonon relaxation or cross relaxation processes, to the depopulation of the green band, which feeds and favors the red emission of Er 3+ in the up‐conversion process.