Regulation of morphologies and luminescence of β-NaGdF4:Ybc+,Er3+ upconversion nanoparticles by hydrothermal method and their dual-mode thermometric properties

Abstract Exploring the thermometric properties of UCNPs is of great importance for non-contact fluoresce thermometers. Ln-doped β-NaGdF 4 :Yb 3+ ,Er 3+ upconversion nanoparticles (UCNPs) have been fabricated by varying the ratio of citric ions to molecules in precursor. Morphology of the as-prepared β-NaGdF 4 :Yb 3+ ,Er 3+ UCNPs turns from hexagonal prisms to agglomerations of smaller particles with decreased dimension. Luminescence intensity decreases and red-to-green ratio increases with increasing ratio of citric ions to molecules. A dual-mode thermometric property has been found in the as-prepared β-NaGdF 4 :Yb 3+ ,Er 3+ UCNPs. The first mode derives from the temperature dependent fluoresce-intensity-ratios of thermally coupled manifolds of Er 3+ ( 2 H 11/2 ) and ( 4 S 3/2 ) manifolds, of which the maximum relative sensitivity value is 0.0036 K −1 . The other mode derives from temperature dependent red-to-green ratios, which is a linear function of temperature and the maximum relative sensitivity value is 0.0238 K −1 . The β-NaGdF 4 :Yb 3+ ,Er 3+ UCNPs with morphology of agglomerations of smaller particles with high surface-to-volume ratios show advanced sensitivities, which are suitable for noncontact optical thermometer.