Optical study of spin-flip transitions atFe3+in InP

The 0.5-eV (4000-${\mathrm{cm}}^{\mathrm{-}1}$) emission band in InP:Fe is studied in detail by Fourier-transform infrared photoluminescence (PL), time-resolved PL, and photoluminescence excitation (PLE) spectroscopy. We resolve new fine structures in both the zero-phonon (ZP) lines and in the corresponding phonon sideband. The transient PL signal follows an exponential decay with a time constant of 1.1±0.3 ms. The PLE shows that the 0.5-eV band can be pumped via hole capture of ${\mathrm{Fe}}^{2+}$ and even more efficiently by exciting resonantly the charge-transfer states [${\mathrm{Fe}}^{2+}$ ${(}^5$ ${\mathit{T}}_2$),${\mathit{h}}_{\mathit{b}}$], where the hole is bound to ${\mathrm{Fe}}^{2+}$. The results from PLE and the long decay time strongly support the interpretation of the 0.5-eV band as spin-flip transitions ${}_{}{}^4{}_{}{}^{}$ ${\mathit{T}}_1$ ${\to }^6$ ${\mathit{A}}_1$ of ${\mathrm{Fe}}^{3+}$. We explain the fine structure of the ZP lines by a dynamic Jahn-Teller distortion in the excited state ${}_{}{}^4{}_{}{}^{}$ ${\mathit{T}}_1$. The decay of the charge-transfer states [${\mathrm{Fe}}^{2+}$ ${(}^5$ ${\mathit{T}}_2$),${\mathit{h}}_{\mathit{b}}$] leaves the ${\mathrm{Fe}}^{3+}$ ion in an excited state (${\mathrm{Fe}}^{3+}$ ${)}^{\mathrm{*}}$, which pumps the 0.5-eV emission.