Modulation On Spontaneous Emission Of RE Ions By Photonic Crystal

Eversince the birth of photonic crystal, one of its functionalities received constant attentionand continuous research, which is its control over spontaneous emission. Theoretically, the rateof spontaneous emission is proportional to the local photon density of states and photoniccrystal is a powerful tool to manipulate the photon density of states. Currently methods offabrication especially in3D are still limited and large scale production nowadays relies mainlyon the process of flow induced self assembly. The combination of thus-prepared photoniccrystal and Rare-earth emitters offers several promises. First of all, from the perspective offundamental research, Rare-earth emitters with narrowline emission bands offer certainadvatages over broad band emitters, for example they are expected to probe the finer structuresof changes in DOS; it also brings some new perspectives other than the more studied broadbandemitters can, so that hopefully we can approach the issue with a more holistic picture. Secondly,from the perspective of utilitarianism, certain real world devices, like photon sensitizer,directional emitters, color purifiers, photon energy converters, are available from such acombination and before these can be realized, we need to know modulation to what extent cancurrent fabrication technique cater. Based on these concerns, we designed a series ofluminescent photonic crystals and studied systematically their morphology, optical propertiesand effects of photonic stop band on luminescence. The major results are summarized as thefollowing:In our first prject, the TiO₂:Sm³+inverse opal was prepared by the template assisted methodand its modification on photouminescent properties of4f-4f transitions of Sm³+was studied. Thesample morphology was confirm by SEM. Transmittance spectra show a dip within the photonic bandgap, whose location totally shifts to red with the increasing angle between the incident lightand the inverse-opal sample due to uneven shrinkage of lattices. Steady state PL spectra indicatea spatial redistribution of emission lines. Decay kinetics demonstrates that the spontaneousemission rates of Sm³+ions in the inverse opal diminish due to the existence of photonicstopband.In our second project, poly-methyl methacrylate （PMMA） opal PHCs containing uniformlydispersed europium chelate were fabricated with finely controlled photonic stop band （PSB）positions in order to study certain ambiguities regarding weakly opal PHCs. Measurements ofluminescent dynamics and angle resolved/integrated emission spectra as well as numericalcalculations of total density of states （DOS） were performed. We determined that in weaklyopals, the total spontaneous emission rate （SER） of Σ⁵D₀-7^F_Jfor Eu3+was independent of PSBpositions but was higher than that of disorder powder sample, which was attributed to highereffective refractive index in PHC rather than PSB effect. Branch SER of5D0-7F2for Eu³+in thePHCs, on the other hand, was spatially redistributed, suppressed or enhanced in directions ofelevated or reduced optical modes, keeping the angle-integrated total unchanged. All the resultsare in agreement with total DOS approximation.