Using time-resolved photoluminescence measurements, the recombination rate in an In0.18Ga0.82N/GaN quantum well (QW) is shown to be greatly enhanced when spontaneous emission is resonantly coupled to a silver surface plasmon. The rate of enhanced spontaneous emission into the surface plasmon was as much as 92 times faster than normal QW spontaneous emission. A calculation, based on Fermi's golden rule, reveals the enhancement is very sensitive to silver thickness and indicates even greater enhancements are possible for QWs placed closer to the surface metal coating.The spontaneous emission (SE) decay constant τ for radiating dipoles at r e is given by Fermi's golden rulewhere ρ(hω) is the photon density of states (DOS) and f | d · E( r e )|i is the dipole emission matrix element. As pointed out by Purcell, SE may be enhanced by altering the photon DOS 1 . For example, the ratio of enhanced to free space emission (the Purcell factor F ) has been measured as large as 5 in an atomic system by placing the radiating atoms in a high Q, low volume cavity 2,3 . A Purcell factor of up to 6 has been observed from quantum well (QW) and quantum dot emitters in vertical cavity surface emitting laser structures, while an enhancement of 15 has been observed from quantum dots in a microdisk cavity 4,5 . Photonic crystals and distributed Bragg gratings have also been used to enhance the SE rate by as much as a factor of 4.5 6,7,8 . Such enhanced SE rates, achieved by increasing the photonic DOS in a small cavity, permit lower threshold, higher modulation frequency lasers as well as more efficient light emitting diodes.The SE rate can also be modified when semiconductor or dye emitters are coupled to a surface plasmon (SP) of a metallic film 9,10,11,12 . A single QW can experience strong quantum electrodynamic coupling to a SP mode if placed within the SP fringing field penetration depth. An electron-hole pair in the QW recombines and emits a photon into a SP mode instead of into free space. The degree of SE rate modification for a given wavelength depends on the SP DOS at that wavelength. The strongest enhancement occurs near the asymptotic limit of the SP dispersion branch, the SP "resonance" energy E sp , where the SP DOS is very high. Non-resonant, SPmediated SE enhancements as large as 6 have been observed from GaAs QWs near thin Ag films 9 . Even greater enhancements are possible for wide bandgap semiconductors whose emission wavelength is coincident with E sp . In this report, time-resolved photoluminescence (TRPL) measurements of a partially silver-coated InGaN/GaN QW directly demonstrate the SP-mediated resonant enhancement of the SE rate for the first time in a semiconductor QW. An InGaN/GaN QW was used in these experiments, grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrate 13 . Over a 1.5 µm Si-doped GaN buffer layer was grown a 28 nm In 0.04 Ga 0.96 N reference layer, a 6 nm GaN layer, and the 3 nm In 0.18 Ga 0.82 N QW as shown in Fig. 1. Above the QW was a 12 nm Si-doped GaN cap layer, pl...
Colloidal gold nanoparticles (AuNPs) are of interest as non-toxic carriers for drug delivery owing to their advanced properties, such as extensive surface-to-volume ratio and possibilities for tailoring their charge, hydrophilicity and functionality through surface chemistries. To date, various biocompatible polymers have been used for surface decoration of AuNPs to enhance their stability, payloads capacity and cellular uptake. This study describes a facile one-step method to synthesize stable AuNPs loaded with combination of two anticancer therapeutics, -bleomycin and doxorubicin. Anticancer activities, cytotoxicity, uptake and intracellular localization of the AuNPs were demonstrated in HeLa cells. We show that the therapeutic efficacy of the nanohybrid drug was strongly enhanced by the active targeting by the nanoscale delivery system to HeLa cells with a significant decrease of the half-maximal effective drug concentration, through blockage of HeLa cancer cell cycle. These results provide rationale for further progress of AuNPs-assisted combination chemotherapy using two drugs at optimized effective concentrations which act via different mechanisms thus decreasing possibilities of development of the cancer drug resistance, reduction of systemic drug toxicity and improvement of outcomes of chemotherapy.
Poly(N-isopropylacrylamide) (PNIPAM) hydrogel nanospheres response to global temperature stimuli across the low critical solution temperature is studied as the water content in the polymer network is modified. The refractive index of gel nanoparticles was measured as a function of temperature using spectroscopic ellipsometry. The volume of the nanospheres reduces by 40% resulting in a modification of light scattering properties of the medium. A change in temperature from 33 to 34 °C results in a volume contraction of nanospheres which is accompanied by 8–10% enhancement in the refractive index of the gel network.
The synthesis of fluorescent carbon dots-like nanostructures (CNDs) obtained through the laser ablation of a carbon solid target in liquid environment is reported. The ablation process was induced in acetone with laser pulses of 1064, 532, and 355 nm under different irradiation times. Close-spherical amorphous CNDs with sizes between 5 and 20 nm, whose abundance strongly depends on the ablation parameters were investigated using electron microscopy and was confirmed using absorption and emission spectroscopies. The π- π* electronic transition at 3.76 eV dominates the absorption for all the CNDs species synthesized under different irradiation conditions. The light emission is most efficient due to excitation at 3.54 eV with the photoluminescence intensity centered at 3.23 eV. The light emission from the CNDs is most efficient due to ablation at 355 nm. The emission wavelength of the CNDs can be tuned from the near-UV to the green wavelength region by controlling the ablation time and modifying the ablation and excitation laser wavelength.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.