Gold nanoparticles assisted structural and spectroscopic modification in Er~(3+)-doped zinc sodium tellurite glass

摘要

Achieving enhanced spectroscopic properties of rare earth doped inorganic glasses by embedding metallic nanoparticles of controlled sizes is a challenging task. We report the gold (Au) NPs assisted modifications in structural and spectroscopic properties of melt-quench synthesized Er~(3+) doped zinc sodium tellurite glass. The growth of NPs is stimulated via time varying heat treatment at 300 ℃. XRD patterns confirm the amorphous nature of glasses and TEM images manifest the growth of gold NPs with sizes between 6.1 and 10.7 nm. The heat treatment time dependent variations in physical properties are ascribed to the alteration in bonding of non-bridging oxygen ions. The UV-VIS-NIR spectra reveal six absorption peaks centered at 488, 523, 655, 800, 973 and 1533 nm corresponding to the transition from ground state of ~4I_(15/2) to ~4F_(7/2), ~2H_(11/2), ~4F_(9/2), ~4I_(9/2), ~4I_(11/2),. and ~4I_(13/2) excited states of Er~(3+) ions, respectively. Surface plasmon resonance (SPR) bands are observed in the range of 618-632 nm. Judd-Ofelt analyses demonstrate a significant increase of spectroscopic quality factors (0.86-1.05) and branching ratio (0.62-92.38%). The up-conversion emission spectra of Er~(3+) exhibit three prominent peaks of reasonable green (502 nm), a moderate green (546 nm) and a strong red (629 nm). An enhancement in the red band luminescence intensity by a factor of 8.19 and 8.54 times are achieved for 2 and 4 h of heat treatments, respectively. This enhancement is attributed to the SPR effects of gold NPs producing an intense local field in the proximity of Er~(3+) ions and subsequent energy transfer between RE ions and NPs. The FTIR spectra display the presence of vibrational modes for ZnO_4 bonds, Te-O bond in TeO_3 (tp) and TeO_4 (tbp) units and the hydroxyl groups. Excellent features of the results suggest that our method constitute a basis for tunable growth of gold NPs which is exceedingly useful for the optimization of optical and structural properties.