Upconversion/back-transfer losses and emission dynamics in Nd3+-Yb3+ co-doped phosphate glasses for multiple pump channel laser

An active phosphate glass system co-doped with Nd3+ and Yb3+ rare earth, optically active ions was studied using steady-state and time-resolved luminescence spectroscopies. Because this system exhibits great potential for the development of multiple pump channel Yb3+ lasers, this work attempts to identify losses in order to establish the limits of its radiative efficiency. To achieve this, multiple upconverted visible emissions related to Nd3+ ions were observed in experiments carried out under near-infrared excitation at around 800 nm. An analysis was carried out to clarify if these upconverted emissions were governed by excited-state absorption of pump radiation or energy transfer between the rare earth ions. Another potential source of losses is related to energy back-transfer from Yb3+ to Nd3+ ions. However, no evidence of this phenomenon was observed, which is a good result for laser applications. Finally, the luminescence dynamics of the Yb3+ ions were investigated in the framework of fast-diffusion processes.