Search

An efficient near-infrared quantum cutting process by cooperative down-conversion of active Bi3+ and Nd3+ ions was demonstrated in Bi3TeBO9:Nd3+ phosphors. In particular, the near-infrared emission of Nd3+ ions enhanced by Bi3+ ions of a series of novel Bi3TeBO9:Nd3+ microcrystalline powders doped with Nd3+ ions in various concentrations was investigated. In order to investigate the luminescent properties of BTBO:Nd3+ powders, the excitation and emission spectra and the fluorescence decay time were measured and analyzed. In particular, the emission of Bi3TeBO9:Nd3+ at 890 and 1064 nm was excited at 327 nm (via energy transfer from Bi3+ ions) and at 586.4 nm (directly by Nd3+ ions). The highest intensity emission bands in near-infrared were detected in the spectra of Bi3TeBO9:Nd3+ doped with 5.0 and 0.5 at.% of Nd3+ ions upon excitation in ultraviolet and visible spectral range, respectively. The fluorescence decay lifetime monitored at 1064 nm for Bi3TeBO9:Nd3+ powders shows the single- or double-exponential character depending on the concentrations of Nd3+ ions. The possible mechanisms of energy relaxation after excitation Bi3TeBO9:Nd3+ powders in ultraviolet or visible spectral range were discussed. The investigated Bi3TeBO9:Nd3+ phosphors efficiently concentrate the ultraviolet/visible radiation in the near-infrared spectral range and can be potentially used as effective spectral converters. [ABSTRACT FROM AUTHOR]

A series of novel KGd(WO4)2 crystalline powders doped with Yb3+/Tm3+, Yb3+/Er3+ and Yb3+/Ho3+ were synthesized using a modified Pechini method. The monoclinic structure of these compounds was confirmed by XRD. The luminescence properties were investigated by measuring up-conversion luminescence spectra and decay curves. KGd(WO4)2 crystalline powders doped with Yb3+/Tm3+, Yb3+/Er3+ and Yb3+/Ho3+ exhibit effective multicolour up-conversion luminescence in the VIS and NIR spectral ranges under 980 nm excitation. The vibrational properties of the materials were investigated using μ-Raman spectroscopy. The assistance of low energy phonons of the KGd(WO4)2 matrix in the energy transfer processes between the excited manifolds of the Yb3+, Er3+, Tm3+ and/or Ho3+ ions during the up-conversion process was discussed. These results indicate that KGd(WO4)2 powders doped with selected Tm3+, Er3+, Ho3+ and Yb3+ ions may be potentially used as single-component multicolour or white emission phosphors. [ABSTRACT FROM AUTHOR]

A recent surge of interest in surface-enhanced Raman scattering (SERS) has stimulated the search for new systems that can be utilized to fabricate high-performance optical devices. However, the two-dimensional design of the vast majority of SERS-based assemblies has significantly hindered their real-life applicability, motivating the development of three-dimensional volumetric materials. Here, we report selective SERS observed in a volumetric Bi2O3-Ag eutectic composite obtained by the micro-pulling-down method utilizing directional solidification of eutectics. The enhancement of the Raman signal originates from the localized surface plasmon resonance, LSPR, resulting from silver nanoparticles embedded in the composite. The plasmonic origin of the enhancement is confirmed by characteristic features, such as (i) an enhancement magnitude >103, (ii) the correspondence between the Raman bands’ intensity upon excitation by different wavelengths and the localized surface plasmon resonance (LSPR) intensity, and (iii) the occurrence of overtones, which are absent in the as-grown material that does not exhibit LSPR. The examined Bi2O3-Ag eutectic-based composite is obtained by directional solidification using a simple crystal growth technique. It is the first case of a bulk SERS-active material fabricated by crystal growth techniques, which opens new perspectives towards scalable three-dimensional optical elements with tunable properties based on Raman scattering.