We discuss the necessary conditions for a two-level system in the presence of an isotropic band edge to be transparent to a probe laser field. The two-level atom is transparent whenever it is coupled to a reservoir constituted of two parts - a flat and a non-flat density of modes representing a PBG structure. A proposal on the reconstruction of the band edge profile from the experimentally measured susceptibility is also presented.425 3440Kleppner, D., Inhibited spontaneous emission (1981) Phys. Rev. Lett., 47 (4), pp. 233-236Lewenstein, M., Mossberg, T.W., Glauber, R.J., Dynamical suppression of spontaneous emission (1987) Phys. Rev. Lett., 59, pp. 775-778Lewenstein, M., Zakrzewski, J., Mossberg, T.W., Spontaneous emission of atoms coupled to frequency-dependent reservoirs (1988) Phys. Rev. A, 38 (2), pp. 808-819Haroche, S., Kleppner, D., Cavity quantum electrodynamics (1989) Phys. Today, 42, pp. 24-30Harel, G., Kofman, A.G., Kozhekin, A., Kurizki, G., Control of non-Markovian decay and decoherence by measurements and interference (1998) Opt. Express, 2 (9), pp. 355-367Prataviera, G.A., Mizrahi, S.S., Dodonov, V.V., Brinati, J.R., Probing colored noise from the index of refraction of strongly driven two-level atoms (1999) Phys. Rev. A, 60 (5), pp. 4045-4051Lambropoulos, P., Nikolopoulos, G.M., Nielsen, T.R., Bay, S., Fundamental quantum optics in structured reservoirs (2000) Rep. Progr. Phys., 63, pp. 455-503Auffèves-Garnier, A., Simon, C., Gérard, J.-M., Poizat, J.-P., Giant optical nonlinearity induced by a single two-level system interacting with a cavity in the purcell regime (2007) Phys. Rev. A, 75, pp. 0538231-05382316Yablotonovitch, E., Gmitter, T., Photonic band structure: The face-centered-cubic case (1989) Phys. Rev. Lett., 63, pp. 1950-1953Ho, K.M., Chan, C.T., Soukoulis, C.M., Existence of a photonic band gap in periodic dieletric structures (1990) Phys. Rev. Lett., 65 (25), pp. 3152-3155John, S., Wang, J., Quantum electrodynamics near a photonic band gap: Photons bound states and dressed atoms (1990) Phys. Rev. Lett., 64 (20), pp. 2418-2421John, S., Wang, J., Quantum optics of localized light in a photonic band gap (1991) Phys. Rev. B, 43 (16), pp. 12772-12789Mossberg, T.W., Lewenstein, M., Radiative properties of strongly driven atoms in the presence of photonic bands and gaps (1993) J. Opt. Soc. Amer. B Opt. Phys., 10 (2), pp. 340-345Nabiev, R.F., Yeh, P., Sanchez-Mondragon, J.J., Dynamics of the spontaneous emission of an atom into the photon-density-of-states gap: Solvable quantum-electrodynamical model (1993) Phys. Rev. A, 47 (4), pp. 3380-3384John, S., Quang, T., Spontaneous emission near the edge of a photonic band gap (1994) Phys. Rev. Lett., 50 (2), pp. 1764-1767Kofman, A.G., Kurizki, G., Sherman, B., Spontaneous and induced atomic decay in photonic band structures (1994) J. Modern Opt., 41 (2), pp. 353-384John, S., Quang, T., Localization of superradiance near a photonic band gap (1995) Phys. Rev. Lett., 74, pp. 3419-3422John, S., Quang, T., Quantum optical spin-glass state of impurity two-level atoms in a photonic band gap (1996) Phys. Rev. Lett., 76 (8), pp. 1320-1323Tarhan, I.I., Watson, G.H., Photonic band structure of fcc colloidal crystals (1996) Phys. Rev. Lett., 76 (2), pp. 315-318Zhu, S.-Y., Chen, H., Huang, H., Quantum interference effects in spontaneous emission from an atom embedded in a photonic band gap structure (1997) Phys. Rev. Lett., 79 (2), pp. 205-208Paspalakis, E., Kylstra, N.J., Knight, P.L., Transparency near a photonic band edge (1999) Phys. Rev. A, 60 (1), pp. R33-R36Yang, Y., Zhu, S.-Y., Spontaneous emission from a two-level atom in a three-dimensional photonic crystal (2000) Phys. Rev. A, 62, pp. 0138051-01380511Angelakis, D.G., Knight, P.L., Paspalakis, E., Photonic crystals and inhibition of spontaneous emission: An introduction (2004) Contemp. Phys., 45 (4), pp. 303-318Florescu, M., John, S., Resonance fluorescence in photonic band gap waveguide architectures: Engineering the vacuum for all-optical switching (2004) Phys. Rev. A, 69, pp. 0538101-05381021Lee, R.-K., Lai, Y., Fluorescence squeezing spectra near a photonic bandgap (2004) J. Opt. B: Quantum Semiclassical Opt., 6, pp. S715-S721Wang, R., John, S., Engineering the electromagnetic vacuum for controlling light with light in a photonic-band-gap microchip (2004) Phys. Rev. A, 70, pp. 0438051-14380515Garraway, B.M., Dalton, B.J., Theory of non-Markovian decay of a cascade atom in high-q cavities and photonic band gap materials (2006) J. Phys. B: At. Mol. Opt. Phys., 39, pp. S767-S786Alsing, P.M., Cardimona, D.A., Huang, D.H., Quantum interference near a photonic band edge beyond the weak-field approximation (2007) Phys. Rev. A, 76, pp. 0438021-04380214Cheng, S.-C., Wu, J.-N., Yang, T.-J., Hsieh, W.-F., Effect of atomic position on the spontaneous emission of a three-level atom in a coherent photonic-band-gap reservoir (2009) Phys. Rev. A, 79, pp. 0138011-0138019Wu, J.-N., Huang, C.-H., Cheng, S.-C., Hsieh, W.-F., Spontaneous emission from a two-level atom in anisotropic one-band photonic crystals: A fractional calculus approach (2010) Phys. Rev. A, 81, pp. 0238271-0238279Zhang, D., Li, J., Ding, C., Yang, X., Control of spontaneous emission from a microwave-field-driven four-level atom in an anisotropic photonic crystal (2012) Phys. Lett. A, 376, pp. 1978-1985Zhang, D., Li, J., Ding, C., Yang, X., Spontaneous emission properties of a driven five-level atom embedded in photonic crystals (2012) Opt. Commun., 285, pp. 3612-3617Englund, D., Fattal, D., Waks, E., Solomon, G., Zhang, B., Nakaoka, T., Arakawa, Y., Vuckovic, J., Controlling the spontaneous emission rate of single quantum dots in a two-dimensional photonic crystal (2005) Phys. Rev. Lett., 95, pp. 0139041-0139044Roy, C., John, S., Microscopic theory of multiple-phonon-mediated dephasing and relaxation of quantum dots near a photonic band gap (2010) Phys. Rev. A, 81, pp. 0238171-02381718Lodahl, P., Stobbe, S., Solid-state quantum optics with quantum dots in photonic nanostructures (2013) Nanophotonics, 2 (1), pp. 39-55Yang, Y., Zhu, S.-Y., Spontaneous emission from a three-level atom in two-band photonic crystals (2000) J. Modern Opt., 47 (9), pp. 1513-1547Huang, X.-S., Liu, H.-L., Ding, C.-X., The control of spontaneous emission from a three-level atom in an anisotropic photonic crystal with two asymmetric bands (2013) J. Modern Opt., 60 (2), pp. 128-135Entezar, S.R., Tajalli, H., Probe absorption-dispersion spectra of a driven three-level atom in a double-band photonic crystal (2006) J. Phys. B: At. Mol. Opt. Phys., 39, pp. 2959-2967Wang, Q., Stobbe, S., Lodahl, P., Mapping the local density of optical states of a photonic crystal with single quantum dots (2011) Phys. Rev. Lett., 107, pp. 167404-167407Huisman, S.R., Ctistis, G., Stobbe, S., Mosk, A.P., Herek, J.L., Lagendijk, A., Lodahl, P., Pinkse, P.W.H., Measurement of a band-edge tail in the density of states of a photonic-crystal waveguide (2012) Phys. Rev. B, 86, pp. 1551541-1551545Boyd, R.W., (2008) Nonlinear Optics, , third ed. Academic PressBarnett, S.M., Radmore, P.M., (2002) Methods in Theoretical Quantum Optics, , Oxford University Press OxfordLouisell, W.H., (1973) Quantum Statistical Properties of Radiation, , John Wiley & SonsTiecke, T.G., Thompson, J.D., De Leon, N.P., Liu, L.R., Vuletić, V., Lukin, M.D., Nanophotonic quantum phase switch with a single atom (2014) Nature, 508 (7495), pp. 241-244