The rich magnetic properties of rare-earth orthochromites (RCrO3) have been studied for decades, but luminescence from their rare-earth ions has not been reported. We report the photoluminescence (PL) of faceted microcrystals of the G-type antiferromagnetic orthochromites YCrO3, Yb3+-doped YCrO3, and YbCrO3 (i.e., Y1-xYbxCrO3, 0 ≤ x ≤ 1), prepared via a molten-salt synthesis. The 4 K PL of the Yb3+-containing samples is dominated by narrow multiline f–f emission from Yb3+, with most intensity concentrated into two pronounced lines associated with the 2F5/2(0′) → 2F7/2(0) crystal-field transition that are split by ∼13 cm–1 at 4 K. This splitting is attributed to Cr3+-Yb3+ magnetic exchange coupling, which spontaneously lifts Yb3+ Kramers degeneracies upon ordering of the Cr3+ spin sublattice. The splitting energy decreases with increasing temperature, and the two peaks eventually coalesce at the orthochromite’s magnetic-ordering temperature of TN = 118 – 140 K (depending on composition). All compositions show pronounced Cr3+-Yb3+ simultaneous pair excitation (SPE) bands at 407 nm in their Yb3+ PL excitation (PLE) spectra, with this SPE feature dominating the PLE spectra at room temperature. Variable-temperature PL and PLE measurements reveal that Yb3+ PL sensitization via Cr3+ d–d excitation is ineffective due to efficient nonradiative deactivation of the 2Eg state, whereas simultaneous pair excitation circumvents the need for intervening energy-transfer steps. The ability to monitor lattice spin correlation using Yb3+ PL up to relatively high temperatures suggests exploration of such microstructures as local spin probes, microscale spin-photonic transducers, or magnetically tunable emitters.
Tzanetopoulos et al. (Mon,) studied this question.