Frequency upconversion involving triads and quartets of ions in a Pr3+/Nd3+ codoped fluoroindate glass

Frequency upconversion (UC) processes involving energy transfer (ET) among ${\mathrm{Nd}}^{\text{3+}}$ and ${\mathrm{Pr}}^{\text{3+}}$ ions in a fluoroindate glass are reported. In a first experiment, the excitation of ${\mathrm{Pr}}^{\text{3+}}$ [transition ${}^3{H}_4{\to }^1{D}_2]$ and of ${\mathrm{Nd}}^{\text{3+}}$ [transition ${}^4{I}_{\text{9/2}}{\mathrm{\to (}}^2{G}_{\text{7/2}}{+}^4{G}_{\text{5/2}})$ ] was achieved with a dye laser operating in the 575–590 nm range. In a second experiment, the ${\mathrm{Nd}}^{\text{3+}}$ ions were excited with the second harmonic of a Nd: YAG laser at 532 nm. The ET processes leading to UC in both experiments were studied by monitoring the blue fluorescence decay at 480 nm due to the transition ${}^3{P}_0{\to }^3{H}_4$ in ${\mathrm{Pr}}^{\text{3+}}.$ In the more relevant UC process, quartets of ions (Nd–Nd–Pr–Pr) are excited due to absorption of three laser photons by two ${\mathrm{Nd}}^{\text{3+}}$ ions which transfer their energy to two ${\mathrm{Pr}}^{\text{3+}}$ ions. Each ${\mathrm{Pr}}^{\text{3+}}$ ion promoted to the ${}^3{P}_0$ level decays to the ground state emitting one photon in the blue region. This conclusion was achieved investigating the dependence of the UC fluorescence intensity as a function of laser intensity, samples concentrations, and temporal behavior of the UC signal. Other UC processes involving nonisoionic groups of three ions are also reported.