Infrared emission of single-crystal calcite under broadband short-wavelength excitation

Our results demonstrate that broadband excitation of an oriented calcite single crystal with the radiation from a cw xenon lamp (incident power density of ～1 W/cm²) gives rise to secondary IR emission from the crystal surface. We have measured the IR emission spectrum of a calcite single crystal in two orientations in the range 500–1500 cm^?1 with a resolution of ～1 cm^?1 using a Fourier transform IR spectrometer. The spectrum shows sharp lines arising from IR-active (polar) vibrational transitions in the calcite crystal and can be interpreted in trems of a two-photon decay of a nonpolar vibrational state (A _1g mode) effectively excited through broadband visible pumping. We analyze the ways of raising the efficiency of the conversion of primary (visible) to secondary IR radiation. In particular, this might be achieved using photonic crystals and an excitation frequency near the maximum in their density of states. The new type of IR emission spectroscopy, taking advantage of broadband visible or UV excitation of molecular vibrations in bulk dielectric inorganic materials or materials infiltrated into the pore space of globular photonic crystals, appears to have considerable promise.