Enhanced infrared to visible upconversion emission in Er ~3 doped phosphate glass: Role of silver nanoparticles

摘要

Phosphate glasses with compositions (59.5-x)P _2O _5-MgO-xAgCl-0.5Er _2O _3 (0.0≤x≤1.5 mol) containing fixed concentration of Er ~3 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 ~4I _(13/2), ~4I _(11/2), ~4I _(9/2), ~4F _(9/2), ~4S _(3/2), ~2H _(11/2), ~4F _(7/2), ~4F _(5/2), ~2G _(9/2), ~4G _(11/2) transitions in which the most intense bands are ~2H _(11/2) and ~4G _(11/2). The absorption spectrum of Er ~3 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 (~4S _(3/2~-) ~4I _(15/2)) and red (~4F _(9/2~-) ~4I _(15/2)) centered at 540 nm and 634 nm, respectively, corresponding to Er ~3 transitions. An enhancement in UC emission intensity of green band (~4S _(3/2~-) ~4I _(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 (~4F _(9/2~-) ~4I _(15/2)) is smaller. The enhancement of UC emission is understood in terms of the intensified local field effect due to silver NPs.