Impact of annealing time on silver nanoparticles growth assisted spectral features of erbium-zinc-boro-tellurite glass

Modifying the optical response of rare earth doped inorganic glasses by embedding nanoparticles is a never-ending quest. Accurate size and shape control of metal NPs inside the glass matrix through precise heat treatment (annealing) is challenging. We report for the first time, the effects of annealing time on the optical properties of the Er3+-doped zinc-boro-tellurite glasses containing silver NPs. Glasses are prepared using melt-quenching method where the growth of NPs is tuned by varying heat treatment duration. Modifications in physical, optical, and structural parameters are ascribed to the alteration of non-bridging oxygen due to HT. Shrinkage of NPs sizes from 12.8 to 6.6 nm for annealing time beyond 6 hr at 410 °C is ascribed to their diffusion limited growth. Surface plasmon resonance bands at 550 and 580 nm revealed red shift. The intensity parameters related to the radiative transitions within 4fn configuration of Er3+ ion are determined and analyzed using Judd-Ofelt theory. The room temperature emission spectra under 476 nm excitation exhibited three peaks centered at 536, 550 and 630 nm corresponding to the transitions from 2H11/2, 4S3/2 and 4F9/2 excited states to 4I15/2 ground state. Luminescence intensity enhancement (by a factor as much as 4.52) is majorly attributed to the local field effect of Ag NPs and quenching is due to the energy transfer from NPs to Er3+. Present glass compositions are demonstrated to be promising for the development of photonic devices

Tuning surface plasmon in erbium-boro-tellurite nanoglass via thermal annealing

The demand for tunable surface plasmon (SP) of embedded metal nanoparticles (NPs) in rare earth doped inorganic lasing glasses is ever-growing. Following melt quenching method Er3+ doped zinc-boro-tellurite glasses containing silver (Ag) NPs are prepared. Glasses are heat treated (thermally annealed) at varying temperatures and time duration to alter the NPs morphology which generates SP. The annealing assisted SP resonance mediated modification in spectral features is discerned. Samples heat treatment at 410°C for 6 hrs duration ensures the reduction of Ag+ ions to Ag° NPs. Thermally annealed glasses are characterized via XRD, UV–Vis-IR absorption, photoluminescence spectroscopy, and TEM imaging. XRD spectra confirm the amorphous nature of the glass and TEM image reveals the existence of homogeneously distributed spherically shaped silver NPs of average diameter ~4.5 nm. NPs are found to grow with the increase of both annealing time and temperature. The UV–Vis spectra exhibit seven absorption bands corresponding to 4f–4f transitions of Er3+ ions in the wavelength range of 500-650 nm. The localized SPR band is evidenced at 550 and 580 nm. Heat treatment causes a red shift of the plasmon peaks ascribed to the alteration in glass refractive index. Furthermore, the glass sample annealed for 6 hrs displays maximum enhancement in the emission intensity corresponding to the peaks centered at 536 (2H11/2→4I15/2), 550 (4S3/2→4I15/2) and 632 nm (4F9/2→4I15/2). This enhancement is primarily attributed to the local field effect of the silver NPs. Admirable features of the results suggest that our systematic method for heat treatment in tuning NPs size assisted SPR may contribute towards the development of functional glass