Optical detection of cross relaxation between rare-earth ions in lanthanum trichloride crystals

Abstract

The dynamics of relaxation and interionic energy-transfer processes for ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Er}}^{3+}$ ions, dilutely cosubstituted at ${\mathrm{La}}^{3+}$ sites in La${\mathrm{Cl}}_{3}$ single crystals, have been investigated in a series of optical-magnetic double-resonance experiments. These processes have been studied by measuring the effects of electron-paramagnetic-resonance absorption at microwave frequencies on the fluorescence radiation emitted during continuous Ar-ion-laser irradiation. In cases for which the ratio of the magnetic field energy splitting of the ground Kramers doublet of ${\mathrm{Er}}^{3+}$ to that of ${\mathrm{Nd}}^{3+}$ had values relatively close to \textonehalf{}, 1, 2, 3, or 4, the time for regaining steady-state-level populations after termination of microwave irradiation was markedly reduced compared with other ratios and was minimum at those particular values. This observation is interpreted as due to energy-conserving cross-relaxation processes involving several ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Er}}^{3+}$ ions simultaneously.