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Cathodoluminescent enhancement of Na3YSi3O9:Tb3+ glass ceramic by Ag nanoislands surface plasmon effect
Materials Letters 160 (2015) 331–334
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Cathodoluminescent enhancement of Na3YSi3O9:Tb3 þ glass ceramic by Ag nanoislands surface plasmon effect Wenyu Zhao a,n, Shengli An b, Bin Fan a, Songbo Li a a b
School of Chemistry and Chemical Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China School of Material and Metallurgical Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 July 2015 Received in revised form 29 July 2015 Accepted 30 July 2015 Available online 31 July 2015
The effects of Ag nanoisland structure on the surface of Na3YSi3O9:Tb3 þ glass ceramic was studied by cathodoluminescence and atomic force microscopy. Under electron beam excitation, the emission spectrum shape and main peaks were not affected by the Ag nanoisland structure, but about a fourfold enhancement in emission intensity was observed. The enhancement factor increased remarkably with increasing accelerating voltage and then stabilized to a constant. However, the increasing filament current did not affect the enhancement factor. These results suggest that surface plasmon resonance is beneficial to improve cathodoluminescent intensity. & 2015 Elsevier B.V. All rights reserved.
Keywords: Optical materials Surface plasmon resonance Luminescence Glass ceramics
1. Introduction Nanometal materials exhibit unique optical and electrical properties that remain unmatched by many traditional materials. They present wide application prospects in the fields of material science, life science, and nanophotonics. Generally, when an external electric field (e.g., light field) acts on Au, Ag, Cu, or other metals, an induced charge will form on the metal surface or interface. In this case, when the metal particle size is smaller than the incident wavelength and the natural vibration frequency is close to the incident wavelength, surface plasmon resonance (SPR) is produced. Charge resonance localized on the surface of the metal nanoparticles or rough metal surface is called the localized surface plasmon (LSP). Its properties depend on particle size, shape, dielectric surroundings, particle composition, and particle spacing. Thus, control can be achieved by changing their carrier, particularly the metal micro/nano structure. Metal nanostructure remarkably enhances the SPR of luminescent materials. With the rapid development of methods for preparing and manipulating nanoscale metal particles, the fluorescence enhancement effect of SPR has gained considerable attention in optics research. This property has been explored in the fabrication of biochemical sensor devices, optical waveguides, high-brightness GaN-based LEDs, solar cells, and so on [1,2]. Among all metals, the SPR n
Corresponding author. E-mail address: [email protected] (W. Zhao).
http://dx.doi.org/10.1016/j.matlet.2015.07.163 0167-577X/& 2015 Elsevier B.V. All rights reserved.
between light and Ag is the strongest; hence, silver LSPR is the focus of many investigations [3]. Luminescence intensity tests showed that silver samples enhanced the luminescence effect by the coupling of the LSP resonance with electric dipole transition [4,5]. Red emissions of Sm3 þ ions markedly underwent about a twofold enhancement in luminescence intensity in the nano-Auembedded bulk antimony glass ceramics [6]. However, the SPR luminescence enhancement of nanometal particles inserted with luminescent materials for field emission display (FED) has not been reported previously. In this paper, we report the cathodoluminescence (CL) enhancement of the glass ceramic Na3YSi3O9:Tb3 þ by the SPR effect.
2. Experimental 2.1. Preparation The glass ceramic Na3YSi3O9:Tb3 þ (designated as GC-NYSTb) was prepared from analytical reagents Na2CO3, SiO2, 99.99% Y2O3 and Tb4O7, according to a molar composition of 30Na2O–9.2Y2O3– 60SiO2–0.4Tb4O7. All the raw materials were mixed thoroughly and then melted in a platinum crucible at 1550 °C for 3 h. The melt was cast into a steel mold and pressed by a steel plate. Finally, the GC-NYSTb was obtained by annealing at 750 °C for 5 h in a reduced atmosphere (95% N2 and 5% H2) [7]. The GC-NYSTb was polished, cut into pieces with dimensions
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W. Zhao et al. / Materials Letters 160 (2015) 331–334
of 10 mm 10 mm 0.5 mm, and cleaned by deionized water and 5% KOH solution. Before sputtering, the pieces were again washed with deionized water and dried under compressed air spray. The sputtering chamber was initially evacuated to 7 10 4 Pa and purged with argon flow at 20 sccm to a pressure of 0.5 Pa. An Ag thin film was deposited on the GC-NYSTb surface by magnetron sputtering with a pure silver target (99.999%) at a DC power of 30 W. After deposition time at 0.5 or 1 min, a GC-NYSTb with Ag thin film (designated as GC-NYSTb-Ag-film) was obtained. To fabricate GC-NYSTb with Ag nanoislands (designated as GCNYSTb-Ag-islands), the sample GC-NYSTb-Ag-film was annealed at 300 °C for 0.5 h.
2.2. Characterization The atomic force microscopy (AFM) images of sample surfaces were obtained using a Dimension 3100 AFM (Bruker, Santa Barbara, CA, USA). For GC-NYSTb-Ag-islands, the CL was collected from the GC-NYSTb side in an ultrahigh-vacuum chamber (o8.0 10 4 Pa), and an electron beam was excited from the silver surface with a voltage range of 0.5–7.0 kV and filament current range of 10–70 mA. The CL spectrum was recorded by a spectrometer (Shimadzu RF-5301PC) with a charge-coupled device camera through an optical fiber. All measurements were performed at room temperature.
3. Results and discussion Fig. 1 shows the AFM images of sample surfaces for the GCNYSTb-Ag-film (a) and GC-NYSTb-Ag-islands (b, c). Without annealing, the GC-NYSTb-Ag-film (a) surface displays a continuous layer of Ag thin film with the average thickness of 14 nm. After annealing, the GC-NYSTb-Ag-island surface exhibits Ag nanoisland structure. The average Ag-island heights of sample b and c are about 45 nm and 61 nm, respectively. The sizes of Ag-island increase as the deposition time increases. Fig. 2 shows the CL spectra of samples (a) GC-NYSTb and (b,c) GC-NYSTb-Ag-islands. Under electron beam excitation, all emission spectra show the f–f characteristic transitions of Tb3 þ , such as electric-dipole (ED) transition 5D4-7F6 and magnetic-dipole (MD) transition 5D4-7F5 [7,8]. For Ag, the electron penetration depth can be estimated by the empirical formula: Re (nm)¼25(A/ρ)(E/Z1/2)n, where n¼1.2/(1 0.29 log10 Z), A is the molecular weight (107.8), ρ is the bulk density (10.53 g/cm3), Z is the atomic number (47), and E is the accelerating voltage (kV). Re ¼73.3 nm when E¼4 kV. The electrons can penetrate the Ag nanoislands and reach the surface of GC-NYSTb based on Fig. 1. The shape and emission wavelengths are not affected by the Ag nanoisland structure because the characteristic transitions of Tb3 þ can be excited. For the GC-NYSTb-Ag-islands sample, Tb3 þ ions occupy the C2v site symmetry with four different local sites [9]. More importantly, the CL intensity and asymmetric ratios increase as the deposition time increases due to the localized SPR at the GC-NYSTb/Ag interface [5]. About a fourfold enhancement of 547 nm emission is obtained at 1 min. Under
Fig. 1. AFM images of sample surfaces for GC-NYSTb-Ag-film (a) 1 min; GC-NYSTb-Ag-islands (b) 0.5 min and (c) 1 min.
W. Zhao et al. / Materials Letters 160 (2015) 331–334
Fig. 2. CL spectra of samples GC-NYSTb (a), and GC-NYSTb-Ag-islands (b) 0.5 min and (c) 1 min. (Inset table shows asymmetric ratios: I492 nm/I547 nm).
electron beam excitation, many electrons and holes can be produced. Different recombination energy from different electron–hole pairs (EHs) will cause electron transition from ground state to different excited states, or disappear by non-radiative transition (including non-radiative multi/phonon). With the Ag nanoisland structure, light emission of SPR can be excited by fast electrons [10]. Moreover, the EHs recombination may produce SP polaritons (SPPs) instead of photons or phonons because of faster SPPs formation rate [1,11]. Therefore, SP was excited at the Ag/GC interface by electron beam. When an electron leaps into the excited state, the coupling rate of electron–SP (Ksp) becomes far greater than its emission rate (Krad′) and non-radiative transition rate (knon′). Afterward, the excited SPP transforms to light by inducing the excited state of Tb3 þ . The light matches well with the emission wavelength of Tb3 þ . The CL intensity was increased by internal quantum efficiency (IQE). ηIQE′¼(krad′þCextKsp)/(krad′þ knon′þ Ksp)E1 when the extraction efficiency of the excited SPP transforming to light Cext E1 because of high conversion efficiency of the SP mode energy into the energy of photons [1]. Fig. 3 shows the CL intensities of samples GC-NYSTb (a) GCNYSTb-Ag-islands (c) as a function of the accelerating voltage and
Fig. 3. CL intensities of GC-NYSTb (a) and GC-NYSTb-Ag-islands (c) as a function of the accelerating voltage and the enhancement factor by the Ag nanoisland structure (filament current¼ 40 mA).
333
the enhancement factor by the Ag nanoisland structure. At a fixed filament current of 40 mA, all CL intensities increase with increasing accelerating voltages from 0.5 kV to 7.0 kV. The calculated Re values for accelerating voltages 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, and 7.0 kV are 0.6, 2.9, 14.6, 37.5, 73.3, 123.3, 188.6, and 270.1 nm, respectively. The electron beams cannot penetrate Ag nanoislands at accelerating voltages of 0.5–3.0 kV, but can reach the surface of GC-NYSTb through the gaps between the Ag nanoislands. With increasing accelerating voltage, deeper electron penetration corresponds to higher plasma production. This phenomenon produces more secondary electrons and holes, which cause greater Tb3 þ ion emission. More importantly, the enhancement factor from the insertion of the Ag nanoisland structure exhibits a linear increase from 0.5 kV to 4.0 kV and then became virtually constant from 4.0 kV to 7.0 kV. According to previous analysis SP coupling effect can enhance the CL intensity through the Ag nanoislands at the surface of GC-NYSTb. With increasing accelerating voltage, SP coupling effect increases because of a concomitant increase in excited states of Tb3 þ in the GC-NYSTb-Ag-islands. However, at accelerating voltages higher than 4.0 kV, electron beams can penetrate Ag nanoislands. At this point, the excited state of Tb3 þ and the SP coupling effect reach their saturation at the GC-NYSTb/Ag interface, resulting in a plateau of the enhancement factor. Fig. 4 shows the CL intensities of samples GC-NYSTb (a) and GC-NYSTb-Ag-islands (c) as a function of the filament current and the enhancement factor from the insertion of Ag nanoisland structure. All the CL intensities increase with increasing filament current from 10 mA to 70 mA. According to the equation for CL intensity (LCL): LCL ¼f(Ib)(U–U0)m, where U0, f(Ib), and U are “dead voltage,” electron beam current, and accelerating voltage, respectively, the increase in CL intensity with increase in filament current is attributed to the concomitant increase in electron beam current f(Ib). Based on the CL mechanism, secondary electrons induce charge accumulation, change electric field distribution, and produce ions when the conductivity is poor. This results in cathode damage from ion bombardment. Thus, the presence of Ag nanoislands on the surface GC-NYSTb increases conductivity and consequently enhances CL emission. However, Ag nanoislands improve CL intensity only up to a certain extent, after which CL intensity remains constant.
Fig. 4. CL intensities of GC-NYSTb (a) and GC-NYSTb-Ag-islands (c) as a function of the filament current and the enhancement factor from the insertion of Ag nanoisland structure (accelerating voltage¼4 kV).
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W. Zhao et al. / Materials Letters 160 (2015) 331–334
4. Conclusions
References
Samples of GC-NYSTb-Ag-islands were prepared by annealing at 300 °C for 0.5 h. Under electron beam excitation, the GC-NYSTbAg-islands exhibited the characteristic emissions of Tb3 þ , but also the high CL intensity. CL intensity augments with increasing accelerating voltage and filament current. The influence of the accelerating voltage on the enhancement factor is greater than that of the filament current. All results indicate that the fabricated GCNYSTb-Ag-islands have potential applications in FED devices.
[1] I.-H. Lee, L.W. Jang, A.Y. Polyakov, Nano Energy 13 (2015) 140–173. [2] H.-W. Chen, C.-Y. Hong, C.-W. Kung, C.-Y. Mou, K.C.-W. Wu, K.-C. Ho, J. Power Sources 288 (2015) 221–228. [3] L.X. Mao, M. Rycenga, S.E. Skrabalak, B. Wiley, Y.N. Xia, Annu. Rev. Phys. Chem. 60 (2009) 167–192. [4] S.M. Lee, K.C. Choi, Opt. Express 18 (2010) 12144–12152. [5] S.M. Lee, K.C. Choi, D.H. Kim, D.Y. Jeon, Opt. Express 19 (2011) 13209–13217. [6] T. Som, B. Karmakar, Appl. Surf. Sci. 255 (2009) 9447–9452. [7] W.Y. Zhao, S.Li An, B. Fan, S.B. Li, J. Alloy. Compd. 566 (2013) 142–146. [8] G. Lakshminarayana, J.R. Qiu, M.G. Brik, I.V. Kityk, J. Phys.: Condens. Mater. 20 (2008) 335106–335116. [9] Z.Y. Zhang, Y.H. Wang, J.C. Zhang, Y. Hao, Mater. Res. Bull. 43 (2008) 926–931. [10] N. Yamamoto, T. Suzuki, Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe-EQEC 2009. European Conference on IEEE (2009)1. [11] K. Okamoto, Y. Kawakami, IEEE J. Sel. Top. Quant. 15 (2009) 1199–1209.
Acknowledgments This work was supported by the Natural Science Foundation of Inner Mongolia 2014MS0209.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Cathodoluminescent enhancement of Na3YSi3O9:Tb3 þ glass ceramic by Ag nanoislands surface plasmon effect Wenyu Zhao a,n, Shengli An b, Bin Fan a, Songbo Li a a b
School of Chemistry and Chemical Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China School of Material and Metallurgical Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China
art ic l e i nf o
a b s t r a c t
Article history: Received 8 July 2015 Received in revised form 29 July 2015 Accepted 30 July 2015 Available online 31 July 2015
The effects of Ag nanoisland structure on the surface of Na3YSi3O9:Tb3 þ glass ceramic was studied by cathodoluminescence and atomic force microscopy. Under electron beam excitation, the emission spectrum shape and main peaks were not affected by the Ag nanoisland structure, but about a fourfold enhancement in emission intensity was observed. The enhancement factor increased remarkably with increasing accelerating voltage and then stabilized to a constant. However, the increasing filament current did not affect the enhancement factor. These results suggest that surface plasmon resonance is beneficial to improve cathodoluminescent intensity. & 2015 Elsevier B.V. All rights reserved.
Keywords: Optical materials Surface plasmon resonance Luminescence Glass ceramics
1. Introduction Nanometal materials exhibit unique optical and electrical properties that remain unmatched by many traditional materials. They present wide application prospects in the fields of material science, life science, and nanophotonics. Generally, when an external electric field (e.g., light field) acts on Au, Ag, Cu, or other metals, an induced charge will form on the metal surface or interface. In this case, when the metal particle size is smaller than the incident wavelength and the natural vibration frequency is close to the incident wavelength, surface plasmon resonance (SPR) is produced. Charge resonance localized on the surface of the metal nanoparticles or rough metal surface is called the localized surface plasmon (LSP). Its properties depend on particle size, shape, dielectric surroundings, particle composition, and particle spacing. Thus, control can be achieved by changing their carrier, particularly the metal micro/nano structure. Metal nanostructure remarkably enhances the SPR of luminescent materials. With the rapid development of methods for preparing and manipulating nanoscale metal particles, the fluorescence enhancement effect of SPR has gained considerable attention in optics research. This property has been explored in the fabrication of biochemical sensor devices, optical waveguides, high-brightness GaN-based LEDs, solar cells, and so on [1,2]. Among all metals, the SPR n
Corresponding author. E-mail address: [email protected] (W. Zhao).
http://dx.doi.org/10.1016/j.matlet.2015.07.163 0167-577X/& 2015 Elsevier B.V. All rights reserved.
between light and Ag is the strongest; hence, silver LSPR is the focus of many investigations [3]. Luminescence intensity tests showed that silver samples enhanced the luminescence effect by the coupling of the LSP resonance with electric dipole transition [4,5]. Red emissions of Sm3 þ ions markedly underwent about a twofold enhancement in luminescence intensity in the nano-Auembedded bulk antimony glass ceramics [6]. However, the SPR luminescence enhancement of nanometal particles inserted with luminescent materials for field emission display (FED) has not been reported previously. In this paper, we report the cathodoluminescence (CL) enhancement of the glass ceramic Na3YSi3O9:Tb3 þ by the SPR effect.
2. Experimental 2.1. Preparation The glass ceramic Na3YSi3O9:Tb3 þ (designated as GC-NYSTb) was prepared from analytical reagents Na2CO3, SiO2, 99.99% Y2O3 and Tb4O7, according to a molar composition of 30Na2O–9.2Y2O3– 60SiO2–0.4Tb4O7. All the raw materials were mixed thoroughly and then melted in a platinum crucible at 1550 °C for 3 h. The melt was cast into a steel mold and pressed by a steel plate. Finally, the GC-NYSTb was obtained by annealing at 750 °C for 5 h in a reduced atmosphere (95% N2 and 5% H2) [7]. The GC-NYSTb was polished, cut into pieces with dimensions
332
W. Zhao et al. / Materials Letters 160 (2015) 331–334
of 10 mm 10 mm 0.5 mm, and cleaned by deionized water and 5% KOH solution. Before sputtering, the pieces were again washed with deionized water and dried under compressed air spray. The sputtering chamber was initially evacuated to 7 10 4 Pa and purged with argon flow at 20 sccm to a pressure of 0.5 Pa. An Ag thin film was deposited on the GC-NYSTb surface by magnetron sputtering with a pure silver target (99.999%) at a DC power of 30 W. After deposition time at 0.5 or 1 min, a GC-NYSTb with Ag thin film (designated as GC-NYSTb-Ag-film) was obtained. To fabricate GC-NYSTb with Ag nanoislands (designated as GCNYSTb-Ag-islands), the sample GC-NYSTb-Ag-film was annealed at 300 °C for 0.5 h.
2.2. Characterization The atomic force microscopy (AFM) images of sample surfaces were obtained using a Dimension 3100 AFM (Bruker, Santa Barbara, CA, USA). For GC-NYSTb-Ag-islands, the CL was collected from the GC-NYSTb side in an ultrahigh-vacuum chamber (o8.0 10 4 Pa), and an electron beam was excited from the silver surface with a voltage range of 0.5–7.0 kV and filament current range of 10–70 mA. The CL spectrum was recorded by a spectrometer (Shimadzu RF-5301PC) with a charge-coupled device camera through an optical fiber. All measurements were performed at room temperature.
3. Results and discussion Fig. 1 shows the AFM images of sample surfaces for the GCNYSTb-Ag-film (a) and GC-NYSTb-Ag-islands (b, c). Without annealing, the GC-NYSTb-Ag-film (a) surface displays a continuous layer of Ag thin film with the average thickness of 14 nm. After annealing, the GC-NYSTb-Ag-island surface exhibits Ag nanoisland structure. The average Ag-island heights of sample b and c are about 45 nm and 61 nm, respectively. The sizes of Ag-island increase as the deposition time increases. Fig. 2 shows the CL spectra of samples (a) GC-NYSTb and (b,c) GC-NYSTb-Ag-islands. Under electron beam excitation, all emission spectra show the f–f characteristic transitions of Tb3 þ , such as electric-dipole (ED) transition 5D4-7F6 and magnetic-dipole (MD) transition 5D4-7F5 [7,8]. For Ag, the electron penetration depth can be estimated by the empirical formula: Re (nm)¼25(A/ρ)(E/Z1/2)n, where n¼1.2/(1 0.29 log10 Z), A is the molecular weight (107.8), ρ is the bulk density (10.53 g/cm3), Z is the atomic number (47), and E is the accelerating voltage (kV). Re ¼73.3 nm when E¼4 kV. The electrons can penetrate the Ag nanoislands and reach the surface of GC-NYSTb based on Fig. 1. The shape and emission wavelengths are not affected by the Ag nanoisland structure because the characteristic transitions of Tb3 þ can be excited. For the GC-NYSTb-Ag-islands sample, Tb3 þ ions occupy the C2v site symmetry with four different local sites [9]. More importantly, the CL intensity and asymmetric ratios increase as the deposition time increases due to the localized SPR at the GC-NYSTb/Ag interface [5]. About a fourfold enhancement of 547 nm emission is obtained at 1 min. Under
Fig. 1. AFM images of sample surfaces for GC-NYSTb-Ag-film (a) 1 min; GC-NYSTb-Ag-islands (b) 0.5 min and (c) 1 min.
W. Zhao et al. / Materials Letters 160 (2015) 331–334
Fig. 2. CL spectra of samples GC-NYSTb (a), and GC-NYSTb-Ag-islands (b) 0.5 min and (c) 1 min. (Inset table shows asymmetric ratios: I492 nm/I547 nm).
electron beam excitation, many electrons and holes can be produced. Different recombination energy from different electron–hole pairs (EHs) will cause electron transition from ground state to different excited states, or disappear by non-radiative transition (including non-radiative multi/phonon). With the Ag nanoisland structure, light emission of SPR can be excited by fast electrons [10]. Moreover, the EHs recombination may produce SP polaritons (SPPs) instead of photons or phonons because of faster SPPs formation rate [1,11]. Therefore, SP was excited at the Ag/GC interface by electron beam. When an electron leaps into the excited state, the coupling rate of electron–SP (Ksp) becomes far greater than its emission rate (Krad′) and non-radiative transition rate (knon′). Afterward, the excited SPP transforms to light by inducing the excited state of Tb3 þ . The light matches well with the emission wavelength of Tb3 þ . The CL intensity was increased by internal quantum efficiency (IQE). ηIQE′¼(krad′þCextKsp)/(krad′þ knon′þ Ksp)E1 when the extraction efficiency of the excited SPP transforming to light Cext E1 because of high conversion efficiency of the SP mode energy into the energy of photons [1]. Fig. 3 shows the CL intensities of samples GC-NYSTb (a) GCNYSTb-Ag-islands (c) as a function of the accelerating voltage and
Fig. 3. CL intensities of GC-NYSTb (a) and GC-NYSTb-Ag-islands (c) as a function of the accelerating voltage and the enhancement factor by the Ag nanoisland structure (filament current¼ 40 mA).
333
the enhancement factor by the Ag nanoisland structure. At a fixed filament current of 40 mA, all CL intensities increase with increasing accelerating voltages from 0.5 kV to 7.0 kV. The calculated Re values for accelerating voltages 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, and 7.0 kV are 0.6, 2.9, 14.6, 37.5, 73.3, 123.3, 188.6, and 270.1 nm, respectively. The electron beams cannot penetrate Ag nanoislands at accelerating voltages of 0.5–3.0 kV, but can reach the surface of GC-NYSTb through the gaps between the Ag nanoislands. With increasing accelerating voltage, deeper electron penetration corresponds to higher plasma production. This phenomenon produces more secondary electrons and holes, which cause greater Tb3 þ ion emission. More importantly, the enhancement factor from the insertion of the Ag nanoisland structure exhibits a linear increase from 0.5 kV to 4.0 kV and then became virtually constant from 4.0 kV to 7.0 kV. According to previous analysis SP coupling effect can enhance the CL intensity through the Ag nanoislands at the surface of GC-NYSTb. With increasing accelerating voltage, SP coupling effect increases because of a concomitant increase in excited states of Tb3 þ in the GC-NYSTb-Ag-islands. However, at accelerating voltages higher than 4.0 kV, electron beams can penetrate Ag nanoislands. At this point, the excited state of Tb3 þ and the SP coupling effect reach their saturation at the GC-NYSTb/Ag interface, resulting in a plateau of the enhancement factor. Fig. 4 shows the CL intensities of samples GC-NYSTb (a) and GC-NYSTb-Ag-islands (c) as a function of the filament current and the enhancement factor from the insertion of Ag nanoisland structure. All the CL intensities increase with increasing filament current from 10 mA to 70 mA. According to the equation for CL intensity (LCL): LCL ¼f(Ib)(U–U0)m, where U0, f(Ib), and U are “dead voltage,” electron beam current, and accelerating voltage, respectively, the increase in CL intensity with increase in filament current is attributed to the concomitant increase in electron beam current f(Ib). Based on the CL mechanism, secondary electrons induce charge accumulation, change electric field distribution, and produce ions when the conductivity is poor. This results in cathode damage from ion bombardment. Thus, the presence of Ag nanoislands on the surface GC-NYSTb increases conductivity and consequently enhances CL emission. However, Ag nanoislands improve CL intensity only up to a certain extent, after which CL intensity remains constant.
Fig. 4. CL intensities of GC-NYSTb (a) and GC-NYSTb-Ag-islands (c) as a function of the filament current and the enhancement factor from the insertion of Ag nanoisland structure (accelerating voltage¼4 kV).
334
W. Zhao et al. / Materials Letters 160 (2015) 331–334
4. Conclusions
References
Samples of GC-NYSTb-Ag-islands were prepared by annealing at 300 °C for 0.5 h. Under electron beam excitation, the GC-NYSTbAg-islands exhibited the characteristic emissions of Tb3 þ , but also the high CL intensity. CL intensity augments with increasing accelerating voltage and filament current. The influence of the accelerating voltage on the enhancement factor is greater than that of the filament current. All results indicate that the fabricated GCNYSTb-Ag-islands have potential applications in FED devices.
[1] I.-H. Lee, L.W. Jang, A.Y. Polyakov, Nano Energy 13 (2015) 140–173. [2] H.-W. Chen, C.-Y. Hong, C.-W. Kung, C.-Y. Mou, K.C.-W. Wu, K.-C. Ho, J. Power Sources 288 (2015) 221–228. [3] L.X. Mao, M. Rycenga, S.E. Skrabalak, B. Wiley, Y.N. Xia, Annu. Rev. Phys. Chem. 60 (2009) 167–192. [4] S.M. Lee, K.C. Choi, Opt. Express 18 (2010) 12144–12152. [5] S.M. Lee, K.C. Choi, D.H. Kim, D.Y. Jeon, Opt. Express 19 (2011) 13209–13217. [6] T. Som, B. Karmakar, Appl. Surf. Sci. 255 (2009) 9447–9452. [7] W.Y. Zhao, S.Li An, B. Fan, S.B. Li, J. Alloy. Compd. 566 (2013) 142–146. [8] G. Lakshminarayana, J.R. Qiu, M.G. Brik, I.V. Kityk, J. Phys.: Condens. Mater. 20 (2008) 335106–335116. [9] Z.Y. Zhang, Y.H. Wang, J.C. Zhang, Y. Hao, Mater. Res. Bull. 43 (2008) 926–931. [10] N. Yamamoto, T. Suzuki, Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe-EQEC 2009. European Conference on IEEE (2009)1. [11] K. Okamoto, Y. Kawakami, IEEE J. Sel. Top. Quant. 15 (2009) 1199–1209.
Acknowledgments This work was supported by the Natural Science Foundation of Inner Mongolia 2014MS0209.