Optical detected ESR in the4 S 3/2 excited state of Er:YCl3

The electron spin resonance in the⁴ S _3/2 excited state of Er³⁺ in yttrium trichloride was studied by optical detection techniques. From angular dependence of the resonance field the principle value of theg-tensor in direction of the twofold crystal axis was deduced to beg∥=3.350±0.004 and the perpendicular valueg⊥ in the crystallographica-b-plane was extrapolated to beg⊥=2.857±0.004. The lifetime of the excited state is found to be temperature independent with τ _r =(1.62±0.02)·10^?3 sec and the spin lattice relaxation timeT ₁ was determined in the temperature region 1.5 to 2.1 °K by observing the recovery of the fluorescent light signal after a microwave saturation pulse was switched off.T ₁ is found to follow a direct process with \(T_1^{ - 1} = k \cdot cth\left( {\frac{{\rlap{--} h\omega }}{{2kT}}} \right)\) .