Ultraviolet and visible up-conversion in sol-gel based SiO2-BaY0.78-xGdxYb0.2Tm0.02F5 nano-glass-ceramics

Abstract Sol-gel derived nano-glass-ceramics with composition 95SiO2-5BaY0.78-xGdxYb0.2Tm0.02F5, where x = 0, 0.2, 0.4, 0.6 and 0.78, were obtained after adequate thermal treatments of precursor glasses. X-ray diffraction, transmission electron microscope and energy dispersive X-ray spectroscopy, confirmed the precipitation and distribution of nanocrystals, with sizes around 10–13 nm, in an amorphous silica network. Under excitation at 980 nm, along with blue, red and NIR characteristic up-conversion emissions of Tm3+ ions, intense UV up-conversion emissions coming from 1I6 and 1D2 levels of Tm3+ ions were also observed in all the studied samples. Additionally, when substituting Y3+ by Gd3+ ions, UV up-conversion emissions coming from Gd3+ ions, along with a reduction of the UV up-conversion emissions of Tm3+ ions, were observed, involving an energy transfer process from Yb3+/Tm3+ systems to Gd3+ ions. UC mechanisms and energy transfer processes were confirmed by transient emission and pump power measurements. Moreover, power dependence analysis revealed saturation effects in all up-conversion emissions, even at low pump power. Results suggest that these highly efficient up-conversion nano-glass-ceramics present potential applications as UV-blue solid state laser materials and solid state lighting.