Luminescence of Exchange Coupled Pairs of Transition Metal Ions

Abstract

The influence of exchange interaction between paramagnetic ions on the luminescence properties is investigated for Mn 2ϩ-Mn 2ϩ , Cr 3ϩ-Cr 3ϩ , Cr 3ϩ-Gd 3ϩ , and Mn 2ϩ-Gd 3ϩ pairs. Two effects are reported: shortening of the lifetime of the spin-forbidden emission and a shift of emission lines or bands to a longer wavelength. The shortening of the lifetime of the spin-forbidden emission is important in Mn 2ϩ doped phosphors. For application of Mn 2ϩ-doped phosphors in displays the long lifetime of the Mn 2ϩ emission is a problem. Shortening of the lifetime is possible by exchange coupling with Mn 2ϩ neighbors, or possibly other paramagnetic neighbors. The results reported here show that the lifetime shortening depends on the exchange-coupling parameter J. The strongest coupling is observed in Cr 3ϩ-Cr 3ϩ pairs and the lifetime shortening is strong ͑e.g., in LaAlO 3 :Cr 3ϩ J ϭ 63 cm Ϫ1 and the lifetime is about 30 times shorter for the pair emission͒. The coupling in Mn 2ϩ-Mn 2ϩ and Cr 3ϩ-Gd 3ϩ pairs is weak. Typically, values for J are around 1 cm Ϫ1 and the lifetime is reduced by a factor of 2-10 ͑e.g., J is Ϫ1.0 cm Ϫ1 for exchange coupling between Cr 3ϩ and Gd 3ϩ ; the lifetime of the spin-forbidden Cr 3ϩ emission is 14 ms in GdAlO 3 compared to 56 ms in LaAlO 3 ͒. The lifetime shortening for the Mn 2ϩ emission is not related to the observed red shift for the pair emission. For the Mn 2ϩ-Gd 3ϩ pair the exchange interaction is very weak and no significant lifetime shortening could be measured for Gd 3ϩ-Mn 2ϩ pairs ͑24 ms for the Mn 2ϩ emission in YF 3 vs. 22 ms in GdF 3 ͒.

Optical properties of manganese in barium phosphate glasses

“…3(a)). This is typical of Mn 2+ ions in phos- phors and was previously explained by magnetic interactions between pairs of Mn 2+ ions [6,7,9]. The emission band for glass samples containing 1 mol% of Mn 2 O 3 was observed around 617 nm and for a 10 mol% of Mn 2 O 3 around 663 nm.…”

“…A large spectral bandwidth of nearly 2500 cm À1 is noted. Moreover, a larger red shift of the emission peak is seen (D(1/k) = 1125 cm À1 ) when compared to the 343 cm À1 energy shift observed for MgAl 2 O 4 :Mn 2+ crystals [6]. The corresponding excitation spectra were similar, therefore only one experimental curve is shown in Fig.…”

“…Besides that, Mn 3+ luminescence has been observed in both silicate and borate glasses [5]. Concentration dependence studies of Mn 2+ luminescence in phosphors indicated a lifetime shortening of impurity emission with increasing Mn 2+ [6,7]. This decrease is important for some potential applications in plasma display panels and it was explained as due to magnetic interactions between pairs of Mn 2+ ions.…”

Luminescence of BaAl2O4:Mn2+,Ce3+ phosphor

“…This could be the concentration quenching due to migration of excitation energy from one activator center to another that acts as an energy sink [17]. The increase in Mn 2+ concentration in barium aluminate was not accompanied with the shift in the peak position as reported in case of MgAl 2 O 4 :Mn 2+ [19]. In the present study, the manganese concentration used was probably low enough to cause any peak shift.…”

Spectroscopic and dielectric studies on MnO doped PbO–Nb2O5–P2O5 glass system

“…has also been reported from our laboratory in recent years [7][8][9]. Though Zn 2 SiO 4 crystal is considered as the most suitable host for manganese doping for the luminescence emission [10,11], recently the lasing action of Mn 2+ ions has also been observed in some of the inorganic glasses [12][13][14][15] including phosphate glasses with large quantum luminescence efficiencies even at room temperature. The studies on up conversion emission with manganese ion as sensitizer and rare-earth ions as activators in some phosphate glasses have also been reported earlier [16][17][18].…”