Photoluminescence Investigations of Dy 3+ -Doped Silicate Xerogels and SiO 2 -LaF 3 Nano-Glass-Ceramic Materials.

In this work, the series of Dy 3+ -doped silicate xerogels were synthesized by sol-gel technique and further processed at 350 °C into SiO 2 -LaF 3 :Dy 3+ nano-glass-ceramic materials. The X-ray diffraction (XRD) measurements, along with the thermal analysis, indicated that heat-treatment triggered the decomposition of La(TFA) 3 inside amorphous sol-gel hosts, resulting in the formation of hexagonal LaF 3 phase with average crystal size at about ~10 nm. Based on the photoluminescence results, it was proven that the intensities of blue ( 4 F 9/2 → 6 H 15/2 ), yellow ( 4 F 9/2 → 6 H 13/2 ), and red ( 4 F 9/2 → 6 H 11/2 ) emissions, as well as the calculated yellow-to-blue (Y/B) ratios, are dependent on the nature of fabricated materials, and from fixed La 3+ :Dy 3+ molar ratios. For xerogels, the emission was gradually increased, and the τ( 4 F 9/2 ) lifetimes were elongated to 42.7 ± 0.3 μs (La 3+ :Dy 3+ = 0.82:0.18), however, for the sample with the lowest La 3+ :Dy 3+ molar ratio (0.70:0.30), the concentration quenching was observed. For SiO 2 -LaF 3 :Dy 3+ nano-glass-ceramics, the concentration quenching effect was more visible than for xerogels and started from the sample with the highest La 3+ :Dy 3+ molar ratio (0.988:0.012), thus the τ( 4 F 9/2 ) lifetimes became shorter from 1731.5 ± 5.7 up to 119.8 ± 0.4 μs. The optical results suggest, along with an interpretation of XRD data, that Dy 3+ ions were partially entered inside LaF 3 phase, resulting in the shortening of Dy 3+ -Dy 3+ inter-ionic distances.