Abstract

Several approaches are being attempted to obtain narrow spectral lines and/or controlled spontaneous emission on localized (impurity ions) or delocalized crystal excitations (free electron-hole pairs, excitons). A first way is to quantize electron motion, in an increasing manner in 1, 2 or 3 dimensions, in structures called quantum well,s wires or dots structures. While the approach to quantum wires and dots is being pursued since about 10 years, it did not yield so far any convincing improvement of the optical and optoelectronics properties of solids, in the same way as quantum wells did when compared to “traditional” bulk materials. Another, more recent approach is to remark that broad emission lines and isotropic emission (in the broad sense) are obtained because there is a 3D continuum of photon states available which allow transitions at any direction and energy at which a suitable electronic excitation of the crystal is present. One of the approaches to restrict the available photonic states is that of the photonic bandgap materials, in which the material (more precisely its optical constants) is modulated in all three directions in order to open energy gaps in the propagation of optical waves, identically to the energy gap opening of electron states in solids due to the periodic ion potential. A second way is to bury the light-emitting material in an optical cavity, such that optical modes are separated by more than the emission linewidth. In such a case emission will only occur into one optical mode, with a linewidth detemined by the mode linewidth, and all energy-unmatched crystal excitations will reach this single desexcitation mode through energy and momentum relaxation, as far as non-radiative recombination is negligible.

© 1993 Optical Society of America