The nanostructure of fire opal

Vibrational spectra of opal-based photonic crystals

“…Natural photonic crystal -natural opal is named often opaline silica [2]. However, it could contain different admixtures, variety of SiO 2 phases and shape of the globules is far from regular sphere [3][4][5]. Growing of synthetic opal-like photonic structures is still not a simple task [1,6], therefore natural opals brought from different regions were investigated more frequently than synthetic ones [3][4][5].…”

“…However, it could contain different admixtures, variety of SiO 2 phases and shape of the globules is far from regular sphere [3][4][5]. Growing of synthetic opal-like photonic structures is still not a simple task [1,6], therefore natural opals brought from different regions were investigated more frequently than synthetic ones [3][4][5]. The authors of [7] have pointed out that vibrational spectra of natural opals in terms of a simple superimposition of bands of cristobalite and tridymite phases is irrelevant to a great extent.…”

Nanocrystalline mimetic opals: synthesis and comparative characterization vs. natural stones

“…Fire opal is transparent and characterized by an orange body color, hence its name. This body color originates from the light absorption by needle-like Fe3+-oxides nanoparticles (typically 10 -100 nm) [13]. It is reason which is presented differences between Raman spectrums of natural opal and synthetic, as shown Figure 6.…”

“…Opals used are a semiprecious stone, typical and abundant in México, extracted from the Cerro Viejo mine, near San Juan del Río, state of Queretaro. These stones are commercially known as "fire opal" [13].…”

“…FT-IR spectrum of fire opal is very similar at the above case; however it does not present the absorption band at 620 cm-1, as shown in Figure 4. Hence, natural opal used in this work is part of the opal-CT structural group as described E. Fritsch et al [13]. Figure 5 shows the Raman spectrum of crystalline opal after annealing.…”