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–0.5Er2O3 (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 ∼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 4I13/2, 4I11/2, 4I9/2, 4F9/2, 4S3/2, 2H11/2, 4F7/2, 4F5/2, 2G9/2, 4G11/2 transitions in which the most intense bands are 2H11/2 and 4G11/2. 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 (4S3/2–4I15/2) and red (4F9/2–4I15/2) centered at 540 nm and 634 nm, respectively, corresponding to Er3+ transitions. An enhancement in UC emission intensity of green band (4S3/2–4I15/2) 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 (4F9/2–4I15/2) is smaller. The enhancement of UC emission is understood in terms of the intensified local field effect due to silver NPs.