Inverse opal photonic crystals of Eu3+ doped LaPO4 (LaPO4: Eu）were prepared by a self-assembly technique in combination with a sol-gel method. In the preparation process, Eu3+ doped LaPO4 precursors were filled into the interstices of the opal template assembled by monodispersive polystyrene microspheres. The polystyrene template was then removed by calcination at 650 °C for 5h, meanwhile, Eu3+doped LaPO4 inverse opal photonic crystal was formed. The photoluminescence (PL) from Eu3+ doped LaPO4 inverse opal photonic crystal was studied. The effect of the photonic stop-band on the spontaneous emission of Eu3+ has been observed in the inverse opal photonic crystals of Eu3+ doped LaPO4. Significant suppression of the emission was detected if the photonic band-gap overlaps with the Eu3+ ions emission band.
Considered the model of the one-dimensional photonic crystals (1-D PCs) with double defects, the refractive indexes (n2’, n3’ and n2’’, n3’’) of the double defects were 2.0, 4.0 and 4.0, 2.0 respectively. With parameter n2=1.5, n3=2.5, by theoretical calculations with characteristic matrix method, the results shown that for a certain number (14 was taken) of layers of the 1-D PCs, when the double defects abutted, there was a defect band gap in the stop band gap, while when the double defects separated, there occurred two defect band gaps in the stop band gap; besides, with the separation of the two defects, the transmittance of the double defect band gaps decreased gradually. In addition, in this progress, the frequency range of the stop band gap has a little increase from 0.092 to 0.095.
Different experimental strategies towards the 3-dimensional photonic crystals operating at optical wavelength are classified. The detailed discussion is devoted to the recent progress in photonic crystals fabricated by template method — the photonic band gap materials on the base of opal. The control of photonic properties of opal-based gratings is achieved through impregnating the opal with high refractive index semiconductors and dielectrics. Experimental study demonstrated the dependence of the stop band behaviour upon the type of impregnation (complete or partial) and showed a way for approaching complete photonic band gap. The photoluminescence from opal- semiconductor gratings revealed suppression of spontaneous emission in the gap region with following enhancement of the emission efficiency at the low-energy edge of the gap.
Magnetic-field-tunable photonic stop band in a three-dimensional array of conducting spheres