Structural, optical and mechanical evaluation of solution-combusted NaYF4 as a host matrix for rare-earth doping: Experimental and DFT insights

NaYF 4 nanocrystals were synthesized via solution combustion at 500 °C using stoichiometric amounts of Y(NO 3 ) 3 ·6H 2 O, NaNO 3 , NH 4 F, and urea as fuel. X-ray diffraction (XRD) confirmed the coexistence of cubic and hexagonal (α+β) phases, with an estimated composition of 45.86% α and 54.14% β. Scanning electron microscopy (SEM) revealed irregular morphology with agglomeration. Thermogravimetric analysis (TGA) indicated good thermal stability with minimal weight loss due to water desorption and nitrate decomposition. UV-Vis-NIR spectroscopy showed a wide optical band gap of ∼5.08 eV, suitable for optoelectronic applications. Thermoluminescence (TL) analysis revealed stable electron trapping centers following first-order kinetics, with trap depths confirmed via IR, WGC, and Chen’s methods. To contextualize the experimental findings, density functional theory (DFT) calculations were performed on the hexagonal phase, identified as structurally dominant. The simulations predicted a theoretical indirect band gap of ∼7.47 eV and confirmed mechanical stability through elastic constants satisfying Born’s criteria. A Poisson’s ratio of 0.26 indicated dominant ionic bonding, consistent with the material’s insulating behavior. The presence of both α and β phases did not hinder optical performance, reinforcing the functional viability of mixed-phase NaYF 4 systems. These results highlight NaYF 4 as a stable, transparent host matrix suitable for rare-earth doping in advanced optical and electronic applications. • NaYF 4 nanocrystals synthesized via solution combustion method. • Coexisting cubic and hexagonal phases confirmed by XRD analysis. • Wide optical band gap (5.08 eV) indicates high visible-range transparency. • TL glow peaks at ∼104 °C confirm stable electron traps with first-order kinetics. • DFT results validate high band gap, ionic bonding, and mechanical stability. • First report on mechanical properties of hexagonal NaYF 4 using DFT and experiments.