Nanocomposites and nanomaterials

On photoluminescence of rhodamine 6G and ZnO inside synthetic opal pores and their effective excitation conditions
Derhachov M.P., Ohiienko O.V., Shvets T.V., Roslova E. Yu.
Department of Physics, Electronics and Computer Systems, Oles Honchar Dnipro National University. Prospect Haharina, 72, Dnipro-49010, Ukraine. 
E-mail: derhachov_mp@dnu.dp.ua 

This work is devoted to investigating impact of photonic band-gap structure of synthetic opals on spectral and space distribution of photoluminescence of rhodamine 6G (R6G) molecules and ZnO nanocrystals inside opal pores, and also searching for optimal excitation conditions. 
Synthetic opals with a different grade of structure disordering were soaked in a R6G – ethanol solution (10-4 and 10-5 M). A 532 nm DPSS laser and a 517 nm LED radiation are used for the excitation. The spatial distribution of the R6G emission spectrum is obtained by scanning the excitation radiation through the sample. A stability of dye molecules under the long-time (50 min) laser excitation is studied. The effect of internal and external metallic (copper and silver) resonators on the R6G emission efficiency is also investigated. 
Emission spectrum of laser dye in synthetic opal pores is defined by spectral position of photonic stop-band, by spatial distribution of dye molecules, and by spatial distribution of structure defects. The defects may cause an additional scattering of the exciting and/or emitting photons and result in photon localization. Excitation geometry should be also chosen in a proper way to diminish the re-absorption. The most preferable excitation conditions are found to be the right angle geometry by focusing the exciting radiation into the 0.7 mm thickness layer near by the (111) surface. The existence of internal silver resonators together with the structure disordering may raise the R6G emission efficiency in several times. 
Photoluminescence spectra of ZnO nanocrystals grown in opal matrix from zinc nitrate solution were studied within the 500 nm – 750 nm spectral ranges. An origin of additional bands in the photoluminescence spectra are connected with a recombination through levels, corresponding to defects in the structure of ZnO nanocrystals.