Dynamics of Excited-State Annihilation in NdCl3

Two processes are observed in Nd${\mathrm{Cl}}_3$ whereby two excited ${\mathrm{Nd}}^{3+}$ ions undergo a transition leaving one ion in a higher excited state and the other in a lower state. In one case the initial states are the same, namely ${}_{}{}^4{}_{}{}^{}F_{\frac{3}{2}}^{}{}_{}{}^{}$; in the other they are different, ${}_{}{}^4{}_{}{}^{}F_{\frac{3}{2}}^{}{}_{}{}^{}$ and ${}_{}{}^4{}_{}{}^{}I_{\frac{15}{2}}^{}{}_{}{}^{}$. In both cases fluorescence decays of initial and final states are measured, allowing the determination of the rate equation for the processes.