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Ultra-small niobate based red phosphor showing highly luminescent performance
Materials Letters 124 (2014) 85–88
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Ultra-small niobate based red phosphor showing highly luminescent performance Yiguo Su, Tingting Wang, Xin Xin, Lijuan Yan, Meng Wang, Xiaojing Wang n College of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot, Inner Mongolia 010021, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 7 January 2014 Accepted 14 March 2014 Available online 21 March 2014
This work presented a simple hydrothermal route based on polyoxometalate chemistry of niobium to prepare a novel red phosphor, K2GdNb5O15:Eu3 þ , with ultra-small size and high quantum efficiency. The red/orange (I612/I594) ratio of Eu3 þ emission is 6.8, indicating high color purity and being nearly ideal for the red component in high luminous efficacy white LEDs. The as-measured quantum yield for K2GdNb5O15:Eu3 þ nanoparticles is as high as 63% at Eu3 þ concentration 20%. & 2014 Elsevier B.V. All rights reserved.
Keywords: Ultra-small Nanoparticles Niobate Luminescence
1. Introduction The ever-increasing energy demands and the subsequent global energy crisis have declared a continuous challenge to traditional lighting industry. As an alternative to traditional light sources, solid state lighting devices, especially the white light-emittingdiodes (LEDs), have garnered much research attention due to its low-energy cost, long-lifetime and robust properties [1,2]. Up to date, the development of solid state lighting devices is notably influenced by the discovery of RGB phosphor materials, which have to efficiently absorb in the near UV to blue spectral range. As a key component of the tricolor luminescence, red emitted phosphors currently utilized by industry for GaN LED are Eu2 þ doped nitridosilicates [3]. Recently, particular attention has focused on the engineering of Eu3 þ -doped converting materials [4], since these phosphors have the possibility to improve the luminous efficacy and color rendering index for LEDs. Rare earth niobates and tantalates comprise a large group of metal oxides that exhibit a unique array of characteristics including chemical and electrochemical stability, photocatalytic activity, and luminescence [5]. Eu3 þ could act as a very efficient activator in many niobates and tantalates for high quantum luminescence emission [6]. From the viewpoint of the unprecedented practical applications, it is urgently necessary to explore novel Eu3 þ -doped red niobate phosphors with high quantum efficiency. However, their poor solubility and high crystallization temperature limit the opportunities for soft chemical routes other than solid state processing which hinder discovery of the novel phases in nanosizes. n
Corresponding author. Tel.: þ 86 471 4344579; fax: þ 86 471 4992981. E-mail address: [email protected] (X. Wang).
http://dx.doi.org/10.1016/j.matlet.2014.03.072 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Fortunately, an aqueous synthetic approach based on polyoxometalate chemistry of niobium was developed [7], which is expected to be important for finding novel niobate phosphors. Though a great number of Eu3 þ doped nanophosphors have been investigated, there are very few reports on Eu3 þ doped tetragonal tungsten bronze-type (TTB) structure niobates. Therefore, the present investigation aims at the synthesis and characterization of Eu3 þ doped TTB structure phosphor as well as its luminescent properties. Herein, we report a novel red phosphor, K2GdNb5O15: Eu3 þ (named as KGN: Eu3 þ ), prepared via a facile hydrothermal method and discovered an intensive red emission under near UV excitation which shows a promising application of solid state lighting devices and the relevant technologies.
2. Experimental The typical procedure is described as follows: 0.009 g Eu2O3 (99.99%) and 0.168 g Gd2O3 (99.99%) were dissolved in diluted nitrate acid on heating while stirring, which was allowed to cool down to room temperature. Then, 0.12 g EDTA was added into the mixed solution while stirring. 1.82 g K7HNb3O19 13H2O (prepared according to Ref. [7]) was dissolved in 20 ml deglassed water and slowly dropped in the abovementioned mixed solution with vigorous stirring. At last, 10 ml of 5 M KOH was added to form an almost clear solution. This solution was sealed in 30 ml Teflonlined stainless steel autoclaves and reacted at 200 1C for 24 h. The obtained products were washed with distilled water for several times and dried at 80 1C for 3 h. Eu3 þ doped K2GdNb5O15 samples with different doping levels were also obtained.
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Phase purities were characterized by X-ray power diffraction (XRD) on a Rigaku DMAX2500 X-ray diffractometer using a copper target. Particle sizes and morphologies were determined using transmission electron microscopy (TEM) on a JEM-2010 apparatus with an acceleration voltage of 200 kV. Optical diffuse reflectance spectra were measured using the integrating sphere of a Lambda 900 UV/VIS Spectrometer in the wavelength region between 200 and 800 nm. BaSO4 was used as a reference material. Emission and excitation spectra were measured on an Edinburgh Instruments FLS920 spectrofluorimeter equipped with both continuous (450 W) and pulsed xenon lamps. Absolute quantum yield measurement was made by exciting the samples with diffuse light inside an integrating sphere.
3. Results and discussion Fig. 1a illustrates the transmission electron microscopy (TEM) image of KGN: Eu3 þ nanoparticles. It is observed that all nanoparticles exhibited highly dispersed property. Its selected-area electron diffraction (SAED) shows distinct ring pattern, revealing the polycrystalline nature of KGN:Eu3 þ nanoparticles and the particle size of KGN: Eu3 þ was estimated to be 1–4 nm. The HRTEM image gave further evidence for the polycrystalline behavior of the as-prepared nanoparticles (inset of Fig. 1b, FFT pattern). As seen in Fig. 1b, the spacing between the adjacent lattice fringes of the as-prepared nanoparticles was 0.391 nm, which is very close to that
of 0.3934 nm for K2GdNb5O15. Moreover, EDS data confirmed that the main elemental components are K, Gd, and Nb (Fig. 1c). The signal of C is attributed to the organic surface layers (S1) and Cu from the TEM grid was also detected. EDS maps of KGN: Eu3 þ nanoparticles indicated that all detected signals dispersed homogeneously (S2). In addition, the atomic ratio of K, Gd and Nb determined by EDS was 7.75:3.69:17.64, which confirmed the formation of K2GdNb5O15 compound. Fig. 1d shows the XRD pattern of the KGN: Eu3 þ nanoparticles. The broadened diffraction peaks were observed, demonstrating the fine nature and ultra-small crystal size. To further confirm the phase structure of as-prepared nanoparticles, KGN: Eu3 þ nanoparticles were allowed to grow larger and examined by XRD and HRTEM measurements (S3). The ultra-small size of KGN: Eu3 þ nanoparticles reduces scattering losses, and the flexibility of the crystal structure enables tailoring optical properties, such as broadening the excitation line width [8], which will predict high quantum efficiency. We first investigated the electronic transitions of KGN: Eu3 þ nanoparticles. The absorption edges (Fig. 2a) for KGN: Eu3 þ nanoparticles is located around 310 nm (4.0 eV). Gaussian function fitting indicated that the absorption spectrum consisted of two components, corresponding to the transitions of two types of NbO6 polyhedra in K2GdNb5O15 lattice [9]. The room temperature excitation spectrum of KGN: Eu3 þ is shown in Fig. 2b. A series of sharp lines appeared in the range of 300–550 nm, which are characteristic of f–f transitions of Eu3 þ ions. The full width at the half maximum (FWHM) of the most intense transition at 394 nm (7F0–5L6) is
Fig. 1. TEM image (a), HRTEM image (b), EDS data, (c) and XRD pattern (d) of KGN: Eu3 þ nanoparticles. Inset is the SEAD pattern of KGN: Eu3 þ nanoparticles.
Y. Su et al. / Materials Letters 124 (2014) 85–88
87
Fig. 2. Optical diffuse reflectance spectrum (a), excitation spectrum (b), emission spectrum (c) and lifetime decay curve (d) of KGN: Eu3 þ nanoparticles.
nearly 2 that of the bulk one (S5). The broadened line width increases the absorption cross section of the KGN: Eu3 þ phosphor, which subsequently enhances the luminescence intensity. The corresponding emission spectrum is illustrated in Fig. 2c. The emission spectrum of KGN:Eu3 þ consists of lines ranging from 570 to 720 nm that come from the transitions of 5D0 to 7FJ (J ¼0, 1, 2, 3, 4) levels of the Eu3 þ activators and the intensity ratio of 5 D0–7F2 to 5D0–7F1 is equal to the red/orange (I612/I594 or R/O) ratio. Yan and coworkers systematically investigated the size dependence of color purity in YBO3: Eu under vacuum ultraviolet irradiation. They found that the R/O value increases from 0.577 to 2.761 with decreasing the particle size and demonstrated that a superior color purity can be obtained from the smaller sized YBO3: Eu [10]. Therefore, for the present KGN:Eu3 þ nanocrystals, the value of I612/I594 is 6.8, indicating high color purity and being nearly ideal for the red component in high luminous efficacy white LEDs. Eu3 þ ion has been intensively investigated as a structural probe due to the relative simplicity of its energy level structure and the fact that it possesses nondegenerate ground (7F0) and emitting (5D0) states [11]. The 5D0–7F0 emission line acquires special importance because it reveals the presence of crystallographic inequivalent sites in a given host matrix. As shown in Fig. 2c, 5D0–7F0 transition can be well fitted by a single Gaussian function, indicating Eu3 þ mainly occupied at Gd3þ site (2a, site symmetry: 4/m) in K2GdNb5O15 host matrix [12]. Moreover, Eu3þ ions are likely to
substitute at Gd3 þ site because of the identical charge valence and similar ionic radii of Gd3þ and Eu3þ . The luminescence decay curves of the 5D0 level in Fig. 2d measured on KGN:Eu3þ nanoparticles exhibit multiexponential feature that can be well-reproduced by a double-exponential function as I¼A1 exp( t/τ1)þ A2 exp( t/τ2) (τ1, τ2 correspond to the two different lifetimes of Eu3 þ ions). The calculated values for the lifetimes are τ1 ¼ 0.30 ms (34%) for the short component and τ2 ¼0.63 ms (66%) for the long component. The average lifetime of 5D0–7F2 emission for Eu3 þ can be determined to be 0.51 ms. On the basis of the emission spectrum and the lifetimes of 5D0 emitting level, the quantum efficiency for Eu3 þ in KGN nanoparticles can be calculated to be 73.5% (S5). The luminescence intensities as a function of Eu3 þ content for KGN: Eu3 þ nanoparticles are plotted in Fig. 3. It is clear that the luminescence intensities increased with Eu3 þ concentration to show a maximum at 20%, whereas further increasing the Eu3 þ concentration led to a signification decrease in the luminescence intensities. The much high quenching concentration has already been observed in many rare earth doped nanoparticles, which were ascribed to poor crystallinity and surface effects [13]. The direct view photos demonstrated high quantum yield for KGN: Eu3 þ nanoparticles. The as-measured quantum yield for KGN: Eu3 þ nanoparticles is as high as 63% at Eu3 þ concentration 20%, which is compatible with that observed in EuOF and Eu3 þ doped KLnTa2O7 nanoparticles [6,14].
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Y. Su et al. / Materials Letters 124 (2014) 85–88
Acknowledgment This work is financially supported by NSFC (No. 21103081) and Fujian Provincial Key Laboratory of Nanomaterials (Grant NM10-07).
Appendix A. Supplementary materials Supplementary materials associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet. 2014.03.072.
References [1] [2] [3] [4] Fig. 3. Luminescence intensities as a function of Eu3 þ content. Inset is the direct view photos of the corresponding KGN: Eu3 þ nanoparticles under daylight (a) and excited under a hand-held 365 lamp irradiation: (b) under daylight and (c) in the dark.
4. Conclusion In conclusion, we have originated the synthesis of a novel red phosphor, K2GdNb5O15:Eu3 þ , with ultra-small size. The asprepared K2GdNb5O15: Eu3 þ nanoparticles show high color purity and emit intense red light under near UV excitation. This work may open the opportunities for phosphors with high quantum yields and promise new applications such as solid state lighting devices and displays.
[5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
Schubert EF, Kim JK. Science 2005;308:1274. Taguchi TJ. Light Vis Environ 2003;27:131. Xie RJ, Hirosaki N, Suehiro T, Xu FF, Mitomo M. Chem Mater 2006;18:5578. Wilkinson AJ, Maffeo D, Beeby A, Foster CE, Williams JAG. Inorg Chem 2007;46:9438. Zhu G, Ci Z, Xin S, Wen Y, Wang Y. Mater Lett 2013;91:304. Nyman M, Rodriguez MA, Shea-Rohwer LE, Martin JE, Provencio PP. J Am Chem Soc 2009;131:11652. Nyman M, Rodriguez MA, Alam TM, Anderson TM, Ambrosini A. Chem Mater 2009;21:2201. Cavalli E, Calestani G, Belletti A, Bovero E. J Alloys Compd 2008;451:143. Janka O, Müller-Bunz H, Schleid T. Z Anorg Allg Chem 2010;636:1865. Wei ZG, Sun LD, Liao CS, Jiang XC, Yan CH, Tao Y, et al. J Appl Phys 2003;93:9783. Montini T, Speghini A, Rogatis LD, Lorenzut B, Bettinelli M, Graziani M, et al. J Am Chem Soc 2009;131:13155. Su YG, Li LP, Li GS. Chem Mater 2008;20:6060. Ferdov S, Ferreira RAS, Lin Z. Chem Mater 2006;18:5958. Du YP, Zhang YW, Yan ZG, Sun LD, Yan CH. J Am Chem Soc 2009;131:16364.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Ultra-small niobate based red phosphor showing highly luminescent performance Yiguo Su, Tingting Wang, Xin Xin, Lijuan Yan, Meng Wang, Xiaojing Wang n College of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot, Inner Mongolia 010021, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 7 January 2014 Accepted 14 March 2014 Available online 21 March 2014
This work presented a simple hydrothermal route based on polyoxometalate chemistry of niobium to prepare a novel red phosphor, K2GdNb5O15:Eu3 þ , with ultra-small size and high quantum efficiency. The red/orange (I612/I594) ratio of Eu3 þ emission is 6.8, indicating high color purity and being nearly ideal for the red component in high luminous efficacy white LEDs. The as-measured quantum yield for K2GdNb5O15:Eu3 þ nanoparticles is as high as 63% at Eu3 þ concentration 20%. & 2014 Elsevier B.V. All rights reserved.
Keywords: Ultra-small Nanoparticles Niobate Luminescence
1. Introduction The ever-increasing energy demands and the subsequent global energy crisis have declared a continuous challenge to traditional lighting industry. As an alternative to traditional light sources, solid state lighting devices, especially the white light-emittingdiodes (LEDs), have garnered much research attention due to its low-energy cost, long-lifetime and robust properties [1,2]. Up to date, the development of solid state lighting devices is notably influenced by the discovery of RGB phosphor materials, which have to efficiently absorb in the near UV to blue spectral range. As a key component of the tricolor luminescence, red emitted phosphors currently utilized by industry for GaN LED are Eu2 þ doped nitridosilicates [3]. Recently, particular attention has focused on the engineering of Eu3 þ -doped converting materials [4], since these phosphors have the possibility to improve the luminous efficacy and color rendering index for LEDs. Rare earth niobates and tantalates comprise a large group of metal oxides that exhibit a unique array of characteristics including chemical and electrochemical stability, photocatalytic activity, and luminescence [5]. Eu3 þ could act as a very efficient activator in many niobates and tantalates for high quantum luminescence emission [6]. From the viewpoint of the unprecedented practical applications, it is urgently necessary to explore novel Eu3 þ -doped red niobate phosphors with high quantum efficiency. However, their poor solubility and high crystallization temperature limit the opportunities for soft chemical routes other than solid state processing which hinder discovery of the novel phases in nanosizes. n
Corresponding author. Tel.: þ 86 471 4344579; fax: þ 86 471 4992981. E-mail address: [email protected] (X. Wang).
http://dx.doi.org/10.1016/j.matlet.2014.03.072 0167-577X/& 2014 Elsevier B.V. All rights reserved.
Fortunately, an aqueous synthetic approach based on polyoxometalate chemistry of niobium was developed [7], which is expected to be important for finding novel niobate phosphors. Though a great number of Eu3 þ doped nanophosphors have been investigated, there are very few reports on Eu3 þ doped tetragonal tungsten bronze-type (TTB) structure niobates. Therefore, the present investigation aims at the synthesis and characterization of Eu3 þ doped TTB structure phosphor as well as its luminescent properties. Herein, we report a novel red phosphor, K2GdNb5O15: Eu3 þ (named as KGN: Eu3 þ ), prepared via a facile hydrothermal method and discovered an intensive red emission under near UV excitation which shows a promising application of solid state lighting devices and the relevant technologies.
2. Experimental The typical procedure is described as follows: 0.009 g Eu2O3 (99.99%) and 0.168 g Gd2O3 (99.99%) were dissolved in diluted nitrate acid on heating while stirring, which was allowed to cool down to room temperature. Then, 0.12 g EDTA was added into the mixed solution while stirring. 1.82 g K7HNb3O19 13H2O (prepared according to Ref. [7]) was dissolved in 20 ml deglassed water and slowly dropped in the abovementioned mixed solution with vigorous stirring. At last, 10 ml of 5 M KOH was added to form an almost clear solution. This solution was sealed in 30 ml Teflonlined stainless steel autoclaves and reacted at 200 1C for 24 h. The obtained products were washed with distilled water for several times and dried at 80 1C for 3 h. Eu3 þ doped K2GdNb5O15 samples with different doping levels were also obtained.
86
Y. Su et al. / Materials Letters 124 (2014) 85–88
Phase purities were characterized by X-ray power diffraction (XRD) on a Rigaku DMAX2500 X-ray diffractometer using a copper target. Particle sizes and morphologies were determined using transmission electron microscopy (TEM) on a JEM-2010 apparatus with an acceleration voltage of 200 kV. Optical diffuse reflectance spectra were measured using the integrating sphere of a Lambda 900 UV/VIS Spectrometer in the wavelength region between 200 and 800 nm. BaSO4 was used as a reference material. Emission and excitation spectra were measured on an Edinburgh Instruments FLS920 spectrofluorimeter equipped with both continuous (450 W) and pulsed xenon lamps. Absolute quantum yield measurement was made by exciting the samples with diffuse light inside an integrating sphere.
3. Results and discussion Fig. 1a illustrates the transmission electron microscopy (TEM) image of KGN: Eu3 þ nanoparticles. It is observed that all nanoparticles exhibited highly dispersed property. Its selected-area electron diffraction (SAED) shows distinct ring pattern, revealing the polycrystalline nature of KGN:Eu3 þ nanoparticles and the particle size of KGN: Eu3 þ was estimated to be 1–4 nm. The HRTEM image gave further evidence for the polycrystalline behavior of the as-prepared nanoparticles (inset of Fig. 1b, FFT pattern). As seen in Fig. 1b, the spacing between the adjacent lattice fringes of the as-prepared nanoparticles was 0.391 nm, which is very close to that
of 0.3934 nm for K2GdNb5O15. Moreover, EDS data confirmed that the main elemental components are K, Gd, and Nb (Fig. 1c). The signal of C is attributed to the organic surface layers (S1) and Cu from the TEM grid was also detected. EDS maps of KGN: Eu3 þ nanoparticles indicated that all detected signals dispersed homogeneously (S2). In addition, the atomic ratio of K, Gd and Nb determined by EDS was 7.75:3.69:17.64, which confirmed the formation of K2GdNb5O15 compound. Fig. 1d shows the XRD pattern of the KGN: Eu3 þ nanoparticles. The broadened diffraction peaks were observed, demonstrating the fine nature and ultra-small crystal size. To further confirm the phase structure of as-prepared nanoparticles, KGN: Eu3 þ nanoparticles were allowed to grow larger and examined by XRD and HRTEM measurements (S3). The ultra-small size of KGN: Eu3 þ nanoparticles reduces scattering losses, and the flexibility of the crystal structure enables tailoring optical properties, such as broadening the excitation line width [8], which will predict high quantum efficiency. We first investigated the electronic transitions of KGN: Eu3 þ nanoparticles. The absorption edges (Fig. 2a) for KGN: Eu3 þ nanoparticles is located around 310 nm (4.0 eV). Gaussian function fitting indicated that the absorption spectrum consisted of two components, corresponding to the transitions of two types of NbO6 polyhedra in K2GdNb5O15 lattice [9]. The room temperature excitation spectrum of KGN: Eu3 þ is shown in Fig. 2b. A series of sharp lines appeared in the range of 300–550 nm, which are characteristic of f–f transitions of Eu3 þ ions. The full width at the half maximum (FWHM) of the most intense transition at 394 nm (7F0–5L6) is
Fig. 1. TEM image (a), HRTEM image (b), EDS data, (c) and XRD pattern (d) of KGN: Eu3 þ nanoparticles. Inset is the SEAD pattern of KGN: Eu3 þ nanoparticles.
Y. Su et al. / Materials Letters 124 (2014) 85–88
87
Fig. 2. Optical diffuse reflectance spectrum (a), excitation spectrum (b), emission spectrum (c) and lifetime decay curve (d) of KGN: Eu3 þ nanoparticles.
nearly 2 that of the bulk one (S5). The broadened line width increases the absorption cross section of the KGN: Eu3 þ phosphor, which subsequently enhances the luminescence intensity. The corresponding emission spectrum is illustrated in Fig. 2c. The emission spectrum of KGN:Eu3 þ consists of lines ranging from 570 to 720 nm that come from the transitions of 5D0 to 7FJ (J ¼0, 1, 2, 3, 4) levels of the Eu3 þ activators and the intensity ratio of 5 D0–7F2 to 5D0–7F1 is equal to the red/orange (I612/I594 or R/O) ratio. Yan and coworkers systematically investigated the size dependence of color purity in YBO3: Eu under vacuum ultraviolet irradiation. They found that the R/O value increases from 0.577 to 2.761 with decreasing the particle size and demonstrated that a superior color purity can be obtained from the smaller sized YBO3: Eu [10]. Therefore, for the present KGN:Eu3 þ nanocrystals, the value of I612/I594 is 6.8, indicating high color purity and being nearly ideal for the red component in high luminous efficacy white LEDs. Eu3 þ ion has been intensively investigated as a structural probe due to the relative simplicity of its energy level structure and the fact that it possesses nondegenerate ground (7F0) and emitting (5D0) states [11]. The 5D0–7F0 emission line acquires special importance because it reveals the presence of crystallographic inequivalent sites in a given host matrix. As shown in Fig. 2c, 5D0–7F0 transition can be well fitted by a single Gaussian function, indicating Eu3 þ mainly occupied at Gd3þ site (2a, site symmetry: 4/m) in K2GdNb5O15 host matrix [12]. Moreover, Eu3þ ions are likely to
substitute at Gd3 þ site because of the identical charge valence and similar ionic radii of Gd3þ and Eu3þ . The luminescence decay curves of the 5D0 level in Fig. 2d measured on KGN:Eu3þ nanoparticles exhibit multiexponential feature that can be well-reproduced by a double-exponential function as I¼A1 exp( t/τ1)þ A2 exp( t/τ2) (τ1, τ2 correspond to the two different lifetimes of Eu3 þ ions). The calculated values for the lifetimes are τ1 ¼ 0.30 ms (34%) for the short component and τ2 ¼0.63 ms (66%) for the long component. The average lifetime of 5D0–7F2 emission for Eu3 þ can be determined to be 0.51 ms. On the basis of the emission spectrum and the lifetimes of 5D0 emitting level, the quantum efficiency for Eu3 þ in KGN nanoparticles can be calculated to be 73.5% (S5). The luminescence intensities as a function of Eu3 þ content for KGN: Eu3 þ nanoparticles are plotted in Fig. 3. It is clear that the luminescence intensities increased with Eu3 þ concentration to show a maximum at 20%, whereas further increasing the Eu3 þ concentration led to a signification decrease in the luminescence intensities. The much high quenching concentration has already been observed in many rare earth doped nanoparticles, which were ascribed to poor crystallinity and surface effects [13]. The direct view photos demonstrated high quantum yield for KGN: Eu3 þ nanoparticles. The as-measured quantum yield for KGN: Eu3 þ nanoparticles is as high as 63% at Eu3 þ concentration 20%, which is compatible with that observed in EuOF and Eu3 þ doped KLnTa2O7 nanoparticles [6,14].
88
Y. Su et al. / Materials Letters 124 (2014) 85–88
Acknowledgment This work is financially supported by NSFC (No. 21103081) and Fujian Provincial Key Laboratory of Nanomaterials (Grant NM10-07).
Appendix A. Supplementary materials Supplementary materials associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet. 2014.03.072.
References [1] [2] [3] [4] Fig. 3. Luminescence intensities as a function of Eu3 þ content. Inset is the direct view photos of the corresponding KGN: Eu3 þ nanoparticles under daylight (a) and excited under a hand-held 365 lamp irradiation: (b) under daylight and (c) in the dark.
4. Conclusion In conclusion, we have originated the synthesis of a novel red phosphor, K2GdNb5O15:Eu3 þ , with ultra-small size. The asprepared K2GdNb5O15: Eu3 þ nanoparticles show high color purity and emit intense red light under near UV excitation. This work may open the opportunities for phosphors with high quantum yields and promise new applications such as solid state lighting devices and displays.
[5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
Schubert EF, Kim JK. Science 2005;308:1274. Taguchi TJ. Light Vis Environ 2003;27:131. Xie RJ, Hirosaki N, Suehiro T, Xu FF, Mitomo M. Chem Mater 2006;18:5578. Wilkinson AJ, Maffeo D, Beeby A, Foster CE, Williams JAG. Inorg Chem 2007;46:9438. Zhu G, Ci Z, Xin S, Wen Y, Wang Y. Mater Lett 2013;91:304. Nyman M, Rodriguez MA, Shea-Rohwer LE, Martin JE, Provencio PP. J Am Chem Soc 2009;131:11652. Nyman M, Rodriguez MA, Alam TM, Anderson TM, Ambrosini A. Chem Mater 2009;21:2201. Cavalli E, Calestani G, Belletti A, Bovero E. J Alloys Compd 2008;451:143. Janka O, Müller-Bunz H, Schleid T. Z Anorg Allg Chem 2010;636:1865. Wei ZG, Sun LD, Liao CS, Jiang XC, Yan CH, Tao Y, et al. J Appl Phys 2003;93:9783. Montini T, Speghini A, Rogatis LD, Lorenzut B, Bettinelli M, Graziani M, et al. J Am Chem Soc 2009;131:13155. Su YG, Li LP, Li GS. Chem Mater 2008;20:6060. Ferdov S, Ferreira RAS, Lin Z. Chem Mater 2006;18:5958. Du YP, Zhang YW, Yan ZG, Sun LD, Yan CH. J Am Chem Soc 2009;131:16364.