Efficient quantum splitting and sensitization of ${\mathrm{Gd}}^{3+}$ is demonstrated for the ${\mathrm{Gd}}^{3+}-{\mathrm{Nd}}^{3+}$ system in ${\mathrm{GdLiF}}_4:\mathrm{Nd}2\%$. The quantum splitting results from a two-step cross-relaxation energy transfer between ${\mathrm{Gd}}^{3+}$ and ${\mathrm{Nd}}^{3+}$ that first involves a transition ${}^6\mathrm{G}\to {}^6\mathrm{I}$ on ${\mathrm{Gd}}^{3+}$ and an excitation within the $4f^3$ configuration of ${\mathrm{Nd}}^{3+}$ followed by a second cross-relaxation energy transfer that brings ${\mathrm{Gd}}^{3+}$ to ${}^{6}P_{7∕2}$. The excited ${\mathrm{Nd}}^{3+}$ ion rapidly relaxes, nonradiatively, to the emitting ${}^{4}F_{3∕2}$. The excited ${\mathrm{Gd}}^{3+}$ ion then transfers its energy back to ${\mathrm{Nd}}^{3+}$, which gives rise to the second photon. The process is studied by emission and excitation spectroscopy. The result is a quantum yield for the emission of IR photons, which has its maximum of about $1.05\pm 0.35$, at 175 nm. The dynamics of both the ${\mathrm{Gd}}^{3+}$ and ${\mathrm{Nd}}^{3+}$ excited states are studied in detail, providing information about the mechanisms and rates for the various energy transfer processes. It appears that the second step in the quantum splitting is less efficient than the first. It is found that energy migration among the ${\mathrm{Gd}}^{3+}$ ions plays an important role in the quantum splitting and that there is strong evidence that the exchange interaction is the dominant mechanism in the energy transfer. This system provides excellent insights into the quantum splitting process, especially with regard to an evaluation of the details of the dynamics.

• Received 28 January 2005

DOI:https://doi.org/10.1103/PhysRevB.72.075114