Infrared-to-visible upconversion in Nd3+-doped chalcohalide glasses

Abstract

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.