Surface–plasmon-coupled photoluminescence from CdS nanoparticles with Au films

doi:10.1016/j.ssc.2012.05.008

Solid State Communications

Volume 152, Issue 18, September 2012, Pages 1767-1770

https://doi.org/10.1016/j.ssc.2012.05.008 Get rights and content

Abstract

The enhancement of surface–plasmon-coupled photoluminescence from CdS nanoparticles was examined for various thicknesses of sputtered Au films. The improved luminescence with thickness control of Au correlated well with the increased density of surface–plasmon states, which was modified by the plasmon-dispersion relation at the planar Au/PMMA interface. By annealing the Au films to form a rough surface morphology, the emission in the CdS nanoparticles was further enhanced by the improved excitation and coupling of the surface–plasmon modes.

Highlights

►The surface–plasmon effects on the photoluminescence (PL) of CdS nanoparticles. ► The PL enhancement matches well with the density of surface–plasmon states. ► Further enhanced PL emission was observed with rough Au surface. ► The contribution from the prolonged optical-path lengths was excluded.

Introduction

Over the past few years, surface–plasmon effects have received much attention because they have provided unique optical properties for a wide range of applications, such as light emitting diodes (LEDs), sensor technology, solar cells, and nanophosphors [1], [2], [3], [4], [5], [6], [7], [8]. Surface plasmon modes are waves that propagate along the metallic surfaces; namely, they are essentially light waves trapped on the surface by the collective oscillations of free electrons in the metal with photons through their interactions. These phenomena between the surface charges and light waves make the electromagnetic field decay exponentially with distance from the surface [9]. The electromagnetic fields near metallic surfaces strongly affect the optical properties of semiconductor materials. Thus, the density of surface–plasmon states should be modified to enhance the spontaneous emission rate and improve the quantum efficiency of the semiconductor materials [10].

Strong photoluminescence (PL) emission by surface–plasmon resonance has been reported in several inorganic and organic semiconductors. For example, when Scherer's group changed the type of metal, they obtained a 17-fold enhanced emission of the InGaN quantum wells, which resulted from the energy transfer between the quantum wells and surface plasmons [11]. Pompa's group and Nurmikko's group have shown, respectively, that by using highly ordered gold nanopatterns and periodic Ag nanoparticle arrays, the fluorescence of CdSe/ZnS core/shell quantum dots was enhanced by 30- and 50-fold [12], [13]. Furthermore, several attempts have been made to control the surface–plasmon-resonance frequency by modifying the density of surface–plasmon states with the use of metal alloy, metal-poor cermet, or double metallic layer [14], [15], [16].

On the other hand, to excite surface–plasmon modes by photon momentum [11], [17], special experimental configurations have been designed, such as the dielectric-prism coupler [18], [19], grating coupler [20], [21], [22], and surface roughness [23], [24], [25]. Thus, controlling the density of surface–plasmon states and the plasmon-excitation configuration is considered important for enhancing luminescence properties.

However, there are few reports considering the PL enhancement with respect to the metal-thickness control and its morphological changes at the same time. In this study, the surface–plasmon effects on the PL properties were investigated by varying the thickness and roughness of Au, combining with the theoretical calculations for the uniform interface. The contribution from the prolonged optical paths was also excluded to consider only the surface–plasmon effect on the PL enhancement.

Section snippets

Material and methods

Nearly monodispersed CdS nanoparticles were prepared via a liquid–solid-solution method [26], [27], [28], [29]. Cadmium chloride (CdCl₂, 0.182 g) and sodium sulfide (Na₂S, 0.078 g) were dissolved separately in distilled water (15 ml) by stirring. The CdCl₂ solution was placed into an autoclave with sodium linoleate ((C₁₇H₃₁)COONa, 0.1 g) and linoleic acid ((C₁₇H₃₁)COOH, 0.2 ml) dissolved in ethanol, and then Na₂S solution was added to the resulting solution. The autoclave was sealed and maintained

Results and discussion

Fig. 1(a) shows the PL spectra from the CdS nanocrystals on different thicknesses of as-deposited Au. For comparison, the emission from the CdS nanocrystals on bare glass without Au film is also included. The PL intensity increased with increasing the Au thickness and gradually saturated at 220 nm, ultimately reaching ∼4-fold enhancement at ∼550 nm. However, with annealing of the Au film, the PL spectra were further enhanced (∼6-fold enhanced with 220 nm thick Au), as shown in Fig. 1(b).

The

Conclusions

The surface–plasmon effects on the PL properties of CdS nanoparticles were examined by varying the thickness and roughness of the Au film. The PL enhancement matched well with the density of surface–plasmon states, which increases with the uniform Au-film thickness and gradually saturates above ∼50 nm. By annealing the Au film, further enhanced PL emission was observed due to the improved excitation and coupling of the surface–plasmon modes.

Acknowledgments

We thank Joonhee Moon and Jihang Lee for helpful discussions. This research was supported by the National Research Foundation of Korea, through the World Class University (WCU, R31-2008-000-10075-0) and the Korean Government (MEST: NRF, 2010-0029065).

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Surface–plasmon-coupled photoluminescence from CdS nanoparticles with Au films

Abstract

Highlights

Introduction

Section snippets

Material and methods

Results and discussion

Conclusions

Acknowledgments

Mater. Res. Bull.

Opt. Commun.

Adv. Mater.

Nat. Mater.

Anal. Chem.

Nanotechnology

Appl. Phys. Lett.

Opt. Express

Electron. Mater. Lett.

Nature (London)

Phys. Rev. B

Nat. Mater.

Nat. Nanotechnol.

Nano Lett.

Appl. Phys. Lett.

Appl. Phys. Lett.

Appl. Phys. Lett.

Surface Plasmons on Smooth and Rough Surfaces and on Gratings

Z. Phys.