Optical properties of B2O3-CaF2 glass-ceramics doped with silver nanoparticles and praseodymium ions

We report on the synthesis and optical experiments with borate glass-ceramics (B2O3-CaF2 glass enclosing CaF2 nanocrystals), either undoped or doped with praseodymium ions (Pr3+) and containing silver nanoparticles (Ag-NPs). The techniques of transmission electron microscopy, X-rays diffraction, linear optical absorption, and photoluminescence (PL), were used to characterize the samples prepared. The glass samples, prepared by using the diffusion method, were heat-treated for nucleation of CaF2 nanocrystals (CaF2-NCs) with cubic structure and dimensions of similar to 20 nm, and Ag-NPs (with sizes between similar to 2 and similar to 50 nm). Optical absorption and PL experiments were performed. The glass-ceramic with Ag-NPs, but without Pr3+, exhibited tenfold enhancement (similar to 1000%) of the blue PL from the CaF2-NCs, in comparison with the samples without Ag-NPs. In the samples with Pr3+ the presence of Ag-NPs induced small enhancement of the absorption spectra in the blue region [Pr3+ transitions: H-3(4)-> P-3(J) (J = 0, 1, 2), I-1(6)] and 75% increase of the emitted intensity in the red region (Pr3+ transitions: D-1(2)-> H-3(4)). On the other hand, the CaF2-NCs luminescence was totally quenched due to the presence of Pr3+. This effect was attributed to resonant energy-transfer from the CaF2-NCs to Pr3+. The phenomena observed in the experiments were understood considering the contributions of the local electric field in the vicinities of the Ag-NPs and processes of energy-transfer among the CaF2-NCs, Ag-NPs and Pr3+.

Automated summary

In this study, borate glass-ceramics were synthesized and optical experiments were conducted with doping to modify their properties. The enhancement of blue photoluminescence in CaF2 nanocrystals by adding silver nanoparticles was observed. The introduction of praseodymium ions showed slight enhancement in the blue absorption spectrum and a significant increase in red emission intensity.