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

In this work, the series of Dy-doped silicate xerogels were synthesized by sol-gel technique and further processed at 350 °C into SiO-LaF:Dy 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) inside amorphous sol-gel hosts, resulting in the formation of hexagonal LaF phase with average crystal size at about ~10 nm. Based on the photoluminescence results, it was proven that the intensities of blue (F → H), yellow (F → H), and red (F → H) emissions, as well as the calculated yellow-to-blue (Y/B) ratios, are dependent on the nature of fabricated materials, and from fixed La:Dy molar ratios. For xerogels, the emission was gradually increased, and the τ(F) lifetimes were elongated to 42.7 ± 0.3 μs (La:Dy = 0.82:0.18), however, for the sample with the lowest La:Dy molar ratio (0.70:0.30), the concentration quenching was observed. For SiO-LaF:Dy nano-glass-ceramics, the concentration quenching effect was more visible than for xerogels and started from the sample with the highest La:Dy molar ratio (0.988:0.012), thus the τ(F) 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 ions were partially entered inside LaF phase, resulting in the shortening of Dy-Dy inter-ionic distances.