Intrinsic fluorescence of an Ising antiferromagnet, DyPO4, in a magnetic field

The intrinsic emission of DyP${\mathrm{O}}_4$ has been studied under magnetic field above and below the spin-flip transition. A detailed analysis of the behavior of one of the emission lines corresponding to the ${}_{}{}^4{}_{}{}^{}F_{\frac{9}{2}}^{}{}_{}{}^{}\to {}_{}{}^6{}_{}{}^{}H_{\frac{13}{2}}^{}{}_{}{}^{}$ transition has been performed in the framework of the $3d$ Ising model involving only the nearest-neighbor interactions. The experimental data quite nicely fit this model which was previously proposed by Wright for DyP${\mathrm{O}}_4$. We determine the Ising parameter $J_0$ (exchange and dipolar interactions) for the emitting ${}_{}{}^4{}_{}{}^{}F_{\frac{9}{2}}^{}{}_{}{}^{}$ level and for the sublevels of the ${}_{}{}^6{}_{}{}^{}H_{\frac{13}{2}}^{}{}_{}{}^{}$. A calculation of the dipolar field acting on one ${\mathrm{Dy}}^{3+}$ ion allows us to determine the molecular field corresponding to the exchange interaction, which we show to be the same for different sublevels of the $J=\frac{13}{2}$ states. Our measurements, although being much more difficult than absorption studies (short lifetimes, small quantum efficiencies) lead to a different insight in the DyP${\mathrm{O}}_4$ model and prove to be very useful in this crystal where we could make a quantitative study from emission spectra.