Impact of viscosity on photo-induced bimodal emission, decay profile and energy transfer in lanthanide based hybrid nanostructure

Abstract

The effect of viscous media on fluorescence intensity and lifetime of hybrid nanoparticles (HNPs) have been investigated in order to design viscosity sensor. HNPs are developed by using of Eu(TTA)3Phen (ETP) coordination compound and NaGd0.78Er0.02Yb0.20F4 fluoride nanoparticles. Here ETP gives strong emission in orange-red region at 611 nm wavelength by absorbing ultraviolet (UV) {240–450 nm) photons (known as downshifting process, DS) and NaGd0.78Er0.02Yb0.20F4 nanoparticles give strong emission in green region at about 540 nm wavelength by absorbing near-infrared (980 nm) photons (known as Upconversion process, UC). Small amount of HNPs are dispersed in glycerol-water medium (concentratioñ 10−6 M) and its fluorescence intensity and lifetime are monitored. The viscosity of the system is varied by taking different ratios of glycerol (C3H8O3) and distilled water (H2O). The fluorescence intensity of the colloidal solution is measured by exciting it with UV as well as 980 nm diode laser and found enhancement in emission intensity as a function of increase in relative viscosity. Similarly lifetime also increases with the increase in the relative viscosity of the solvent in both DS and UC processes. The viscosity vs emission intensity/lifetime show exponential increment upon increasing glycerol concentrations. Therefore, the HNPs can serves as fluorescent probe for quantitative measurements of the micro viscosity of environment and thus, it could be extremely useful for the study of biological systems.