Fluorescence line narrowing-Zeeman spectroscopy of Cr3+-doped Gd3Sc2Al3O12 garnet crystals

Abstract

This paper discusses line broadening by compositional disorder and by spin-spin exchange interaction between the paramagnetic Cr3+ and Gd3+ ions in antiferromagnetic Gd3Sc2Al3O12 (GSAG) probed using fluorescence line narrowing (FLN) in the absence and presence of a magnetic field. The most intense R1 lines in Cr3+:GSAG, occurring at lambda =691.2 nm and 692.4 nm, have halfwidths of approximately=32 cm-1. The linewidths of the FLN spectra at 1.6 K are respectively 19 cm-1 and 13 cm-1, much larger than the width of the excitation laser beam (<0.2 cm-1): thus the contributions to the R1-line halfwidth from mechanisms of homogeneous and inhomogeneous broadening are approximately equal. In addition, the peaks of the FLN lines are shifted to lower energy from the laser excitation line by approximately=8 cm-1. As the temperature is increased gradually from 1.6 K to 10 K, the FLN peak is shifted to higher energy and is resonant with the excitation above 10 K. In the presence of an external magnetic field the broad FLN spectrum becomes resolvable into three sharp lines with the width of approximately=3 cm-1 at T=1.6 K. The peak of the line with maximum intensity is coincident with the excitation energy. The FLN spectrum at T=10 K and B=3.46 T is similar to that at T=10 K in the absence of a magnetic field. The temperature dependence and magnetic field dependence of the FLN spectra are discussed in terms of spin-spin exchange interaction between Cr3+ and Gd3+ ions in antiferromagnetic GSAG.