INFLUENCE OF REACTION TEMPERATURE ON OPTICAL ...

Advances in Optics, Photonics, Spectroscopy & Applications VI ISSN 1859 - 4271The XRD patterns of samples after SiO 2 removal indicate a lesser amount of amorphous SiO 2in comparision with the original samples (line 2 in Figs. 3b, c, d). The XRD patterns of thesamples annealed at 1000 and at 1100 o C after SiO 2 removal show a crystobalite structure – theother form of amorphous SiO 2 when annealed at high temperature. In theory, this annealingprocess at high temperature in inert gas might only change the structure of amorphous SiO 2 andnot the weight because no additional oxygen is provided.In order to investigate the photoluminescence of synthesized materials, we measured thesamples at different stages as following: as-grown, after SiO 2 removal in 5% HF for 10 minutes,and after annealing process at 1000 o C and at 1100 o C in Ar gas for 1 hour after removing SiO 2 .Fig. 4a displays PL images among the as-grown samples with different synthesis times. As canbe seen, PL peaks lie in blue region at 390, 430 nm and one small peak at ~ 480 nm. We alsoobserved a higher intensity on the sample having longer synthesis time. In reality, samples withlonger synthesis times have more SiC nanorods than other samples.Figs. 4b, c are PL of the samples with synthesis times of 2.5 and 3 hours. The lines 1, 2, 3, 4are PL of as-grown, after removing SiO 2 in HF solution, annealed at 1000 o C and at 1100 o C inAr gas after SiO 2 removal respectively. The results show that after removing SiO 2 in 5% HFsolution for 10 minutes the PL intensity changed very little. In contrast, after annealing in inertAr gas at high temperature, the intensity increased noticeably. In both cases, the peaks positionsdid not changed. The only difference is that the PL intensity of sample with longer synthesistime, corresponding with larger amount of produced SiC nanorods, experienced a smaller changeafter annealing at high temperature.Intensity (a.u)(a)150010005001230350 400 450 500Wavelength (nm)1- 2 hours2- 2.5 hours3- 3 hoursIntensity (a.u)(b)15001000500021- As -grown for 2.5 hours2- After remov. SiO 23- Anneal. at 1000 o C4- Anneal. at 1100 o C400 500 600 70031Wavelength (nm)4Intensity (a.u.)(c)10000800060004000200001421- As-grown for 3 hours2- After remov. SiO 23- Anneal. at 1000 o C4- Anneal. at 1100 o C3400 500 600 700542Wavelength (nm)Fig. 4. PL of samples with different synthesized times. a: as-grown samples; b: samplesynthesized for 2.5 hours; c: sample synthesized for 3 hoursThe slight change observed in PL intensity and peak position after removing SiO 2 in 5% HFsolution can be explained by suggesting that the removed part of SiO 2 did not contributesignificantly in the PL emission.With the increase in PL intensity after high-temperature annealing in inert gas it can beassessed as follows: In general, high-temperature annealing in inert gas may reduce some of the