We present highly resolved photoluminescence (PL) and absorption spectra of the internal d-d-shell transitions at ${\mathrm{Fe}}^{2+}$ in InP and the related phonon sidebands. By use of the Fourier-transform-infrared technique, the signal-to-noise ratio (SNR) is improved by about two orders of magnitude as compared to conventional dispersive techniques. Thus we are able to resolve new fine structure in the zero-phonon lines of ${\mathrm{Fe}}^{2+}$ in both absorption and PL. This fine structure is identified as shift induced by different iron isotopes. A better SNR also reveals several new features in PL spectra of the phonon sidebands. In absorption measurements ${\mathrm{Fe}}^{2+}$ related spectra in the energetic range of 2800 to 3400 ${\mathrm{cm}}^{\mathrm{-}1}$ (≊0.35–0.4 eV) are recorded, which can be partly attributed to anti-Stokes lines of phonon coupling in emission. Additional peaks at 3103 and 3117 ${\mathrm{cm}}^{\mathrm{-}1}$ are interpreted as transitions from the ${}_{}{}^5{}_{}{}^{}$E ground state to an excited state of the ${}_{}{}^5{}_{}{}^{}$${\mathit{T}}_2$ manifold of ${\mathrm{Fe}}^{2+}$.

• Received 13 August 1990

DOI:https://doi.org/10.1103/PhysRevB.43.2239