Luminescence of erbium doped tellurite glass containing silver nanoparticles

Abstract

Enhancing the optical properties of rare-earth doped inorganic glasses by embedding metallic nanoparticles (NPs) of controlled sizes and examining the mechanism of enhancement are important and challenging. A series of Er3+ doped zinc tellurite glasses with and without silver NPs of molar composition (74.5- x)TeO2-25ZnO-0.5Er2O3-xAgCl with 0 = x = 1.0 mol % were prepared by meltquenching technique. They were characterized by X-ray diffraction, transmission electron microscopy, differential thermal analysis (DTA), and Fourier transform infrared (FTIR), ultraviolet-visible-near infrared and photoluminescence spectroscopy. The thermal, structural, and optical properties of these glasses were determined and analyzed. The XRD pattern confirms the amorphous nature of all samples. The high resolution TEM reveals the presence of silver NPs of average diameter 24 ± 2 nm with measured lattice constant of 2.09 Å and a Gaussian size distribution. The observed glass density ranges from 5.481 to 5.697 g cm-3 and the refractive index evaluated using Sellmeier’s equation varies between 2.16 to 2.27. Thermal parameters such as glass transition temperature (Tg), crystallization temperature (Tc), melting temperature (Tm) and thermal stability ?T (Tc-Tg) were determined from DTA analyses. A wide and stable glass formation range around 87ºC-105ºC was found. The structural properties measured by using FTIR show that as the AgCl content increases, the sharp infrared (IR) absorption peaks were consistently shifted from 675.13 cm-1 to 679.03 cm-1 which were assigned to the structural changes between the stretching vibration mode of TeO4 (trigonal bipyramids) and TeO3(trigonal pyramids). The absorption peaks around 1600 cm-1 and 3400 cm-1 are related to the stretching vibrations of the hydroxyl group participating in the strong metal and hydrogen bonding, respectively. The absorption spectra consist of eight absorption peaks centered at 1510, 975, 799, 655, 586, 523, 489 and 447 nm corresponding to transitions from ground state to 4I13/2, 4I11/2, 4I9/2, 4F9/2, 4S3/2, 2H11/2, 4F7/2, and 4F5/2 excited states, respectively. From PL spectra, excitation at 786 nm and 470 nm for up and down-conversion exhibits strong green and red emission comprised of three emissions band at 501, 548 and 634 nm. The significant enhancement in the luminescence with the increase of AgCl is ascribed to the local field enhancement induced by Ag0 surface plasmon resonance and the energy transfer from fluorescent Ag0?Er3+ ions. The improved optical and structural properties suggest that the studied glasses are potential candidates for nanophotonic devices.