The optical properties of ${\mathrm{Nd}}^{3+}$ ions in six different compositions of glasses based on ${\mathrm{GeO}}_2,$ PbO, and ${\mathrm{Bi}}_2{\mathrm{O}}_3$ have been investigated by using steady-state and time-resolved laser spectroscopy. Judd-Ofelt parameters were derived from the absorption spectra and used to calculate the ${}^4{\overrightarrow{F_{3/2}}}^4{I}_{11/2}$ stimulated emission cross section and the ${}^4{F}_{3/2}$ radiative lifetime. Site-selective spectroscopy and time resolved fluorescence line narrowing experiments were performed in the ${}^4{\overrightarrow{F_{3/2}}}^4{I}_{9/2}{,}^4{I}_{11/2}$ transitions. For all samples studied a line narrowing of the ${}^4{\overrightarrow{F_{3/2}}}^4{I}_{11/2}$ emission has been observed when exciting at the long wave side of the ${}^4{\overrightarrow{I_{9/2}}}^4{F}_{3/2}$ transition. The lifetimes of the ${}^4{F}_{3/2}$ state do not show a monotonic variation with the excitation wavelength indicating large site-to-site variations in the local crystal field. Spectral migration of excitation among the ${\mathrm{Nd}}^{3+}$ ions has been studied from the time evolution of the ${}^4{\overrightarrow{F_{3/2}}}^4{I}_{9/2}$ spectra under resonant excitation. The results can be interpreted in terms of a dipole-dipole energy transfer mechanism. Visible upconversion has been observed in these glasses under infrared laser excitation.

The infrared to visible upconversion processes have been investigated for ${\mathrm{Nd}}^{3+}$-doped chalcohalide glasses with different halide modifiers by using steady-state and time-resolved laser spectroscopy. Two different upconversion mechanisms have been identified depending on the infrared excitation wavelength. When the excitation wavelength is resonant with the ${}^4{F}_{3/2}$ state, three main bands at 538, 600, and 675 nm are observed and attributed to emissions from the ${}^4{G}_{7/2}$ level. These upconverted emissions occur via energy-transfer upconversion involving two neodymium ions in the ${}^4{F}_{3/2}$ state. However, nonresonant excitation at higher energies than that of ${}^4{F}_{3/2}$ state (between states ${}^4{F}_{3/2}$ and ${}^4{F}_{5/2})$ or in resonance with the ${}^4{F}_{5/2}$ state, causes an additional blue emission to originate from the ${}^2{P}_{1/2}$ state. This latter upconverted emission can be attributed to excited-state absorption of the pump radiation. The proposed upconversion mechanisms responsible for the different emissions from levels ${}^2{P}_{1/2}$ and ${}^4{G}_{7/2}$ are supported by both the time evolution of the upconversion luminescence after infrared pulsed excitation and the upconversion luminescence excitation spectra.

In this work, we report on studies of the nature of the dynamics and hydrophobic binding in cyclodextrins and human serum albumin protein complexes with orange II. With femtosecond time resolution, we examined the proton-transfer and trans-cis isomerization reactions of the ligand in these nanocavities and in pure solvents. Because of confinement at the ground state, the orientational motion in the formed phototautomer is restricted, leading to a rich dynamics. Therefore, the emission lifetimes span a large window of tens to hundreds of picoseconds in the cavities. Possible H-bond interactions between the guest and cyclodextrin do not affect the caged dynamics. For the protein–ligand complexes, slow diffusional motion (≈630 ps) observed in the anisotropy decay indicates that the binding structure is not completely rigid, and the embedded guest is not frozen with the hydrophobic pocket. The ultrafast isomerization and decays are explained in terms of coupling motions between N–N and C–N stretching modes of the formed tautomer. We discuss the role of confinement on the trans-cis isomerization with the cavities and its relationships to frequency and time domains of nanostructure emission.