Enhanced infrared to visible upconversion emission in Er3+ doped phosphate glass: Role of silver nanoparticles

Phosphate glasses with compositions (59.5-x)P2O5-MgO-xAgCl-0.5Er(2)O(3) (0.0 <= x <= 1.5 mol%) containing fixed concentration of Er3+ ion with and without silver nanoparticles (NPs) are prepared using melt quenching technique. The amorphous nature of the glass is confirmed using the X-ray diffraction method. The homogeneous distribution of spherical Ag NPs (average size similar to 37 nm) in the glassy matrix is evidenced from the transmission electron microscopy (TEM) analyses. The UV-vis-NIR absorption spectra shows 10 bands corresponding to I-4(13/2), I-4(11/2), I-4(9/2), F-4(9/2), S-4(3/2), H-2(11/2), F-4(7/2), F-4(5/2), (2)G(9/2), (4)G(11/2) transitions in which the most intense bands are H-2(11/2) and (4)G(11/2). The absorption spectrum of Er3+ ions free glass sample containing Ag NPs displays a prominent surface Plasmon resonance (SPR) band located at 528 nm. The infrared to visible frequency upconversion (UC) emission under 797 nm excitation shows two emission bands green (S-4(3/2)-I-4(15/2)) and red (F-4(9/2)-I-4(15/2)) centered at 540 nm and 634 nm, respectively, corresponding to Er3+ transitions. An enhancement in UC emission intensity of green band (S-4(3/2)-I-4(15/2)) is observed in the presence of silver NPs and the maximum enhancement occurred for 1.5 mol% AgCl. However, the enhancement of emission intensity of the red band (F-4(9/2)-I-4(15/2)) is smaller. The enhancement of UC emission is understood in terms of the intensified local field effect due to silver NPs. (C) 2012 Elsevier B.V. All rights reserved.