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In-situ Processing
Published in M S Shur, R A Suris, Compound Semiconductors 1996, 2020
Cadmium fluoride has the same fluorite type of crystal structure as calcium fluoride and energy band gap about 8 eV. Being undoped, it has good insulating properties like CaF2. However its doping with RE ions such as Sm, Gd, or Er results in creation of shallow donor levels (0.15eV), that is quite unusual for a wide band gap crystal. Free electron concentration in the doped CdF2 crystals could exceed 1018 cm-3 [12]. In electric field the electrons can excite the RE ions producing efficient electroluminescence from UV to near IR [13]. Lattice parameter of CdF2 is less than that of Si by 0.8%. Together with the fact that CaF2 lattice parameter is larger than this value for silicon only by 0.6%, it makes very attractive to grow CdF2-CaF2 heterostructures on Si.
Carbon quantum dots functionalized agarose gel matrix for in solution detection of nonylphenol
Published in Environmental Technology, 2020
Sanju Singh, Preeti Nigam, Aisha Pednekar, Souvik Mukherjee, Abhishek Mishra
To study the effect of pH, we prepared blank, 0.001, 0.01, 0.1, 1, 10 mM concentrations of HCl and NaOH separately in pure water. Ten microlitres of CQDs in aqueous solution were added to HCl and NaOH solutions followed by fluorescence measurement. Data were analyzed in terms of percent relative fluorescence compared to the control sample. CQDs were found to be insensitive towards the change in H+/OH- ion concentration (Figure 3(a,b)). Furthermore, on the basis of fluorescence quenching behavior of CQDs, a series of cationic, anionic and organic molecules were tested in aqueous solution. Prepared CQDs showed no quenching effect with lead, cadmium, fluoride or phenol. In addition to cations and anions, potential endocrine disrupters such as nonylphenol, benzene hexachloride and phthalate were tested for change in fluorescence of CQDs. Benzene hexachloride and phthalate showed no quenching activity with control CQDs. However, upon addition of nonylphenol, the fluorescence intensity of the prepared CQDs decreased significantly (Figure 3(c)). The reason for quenching could be several interactions with the quencher molecule-like electron transfer, collisional quenching, excited state reaction and ground state complex formation [22]. On the basis of record change in the fluorescence of the CQDs by nonylphenol, we believed that they may serve as a potential sensor for the molecule. The sensitivity of the nonylphenol sensing was recorded for the quenching of CQD, with the limit of detection of 0.1 µM and a linear range from 0.01 to 1.2 µM. The minimum concentration which could significantly decrease the fluorescence intensity is 0.1 µM (reduction by 20%). The addition of 1 µM nonylphenol to CQDs decreased the relative fluorescence intensity by more than 2 log units (Figure 4(a)). The linear decrease in log fluorescence intensity of CQDs was proportional to the increasing nonylphenol concentration. These results indicate that CQDs have the potential to be used as biosensors for the detection of nonylphenol with a sensitivity of 0.1 µM (30 ng/l). We compared various currently used methods for the detection of nonylphenol with our CQDs based method with respect to sample preparation, an instrument used, detection limit and sensitivity (Table 1). CQDs based detection nonylphenol appears to be a simple, rapid and economical method with reliable sensitivity. However, its sensitivity and detection limit are below par to a highly sophisticated method based on ESI-LC-IT-TOF/MS [15]. Nonylphenol is a threat to the environment and human health as it is non-biodegradable. According to a WHO report, 15 mg/kg/day accumulation of nonylphenol may have an adverse effect on human health. These CQDs could serve as a potential facial probe for the detection of the nonylphenol levels in environmental samples. As our results demonstrate a consistent photoluminescence in a wide pH range, these CQDs may be developed as a suitable sensor for diverse environmental samples.