- Email: [email protected]
Tm) microstructures
Journal Pre-proof Tunable multicolor and white emission NaLuF4:Yb, Nd, Ln (Ln = Er, Tm, Er/Tm) microstructures Guixin Yang, Zhenyu Wu, Dan Yang, Shili Gai, Mengshu Xu, Xiaojun Sun, Piaoping Yang PII:
S1293-2558(18)31271-8
DOI:
https://doi.org/10.1016/j.solidstatesciences.2019.03.010
Reference:
SSSCIE 5860
To appear in:
Solid State Sciences
Received Date: 28 November 2018 Revised Date:
7 March 2019
Accepted Date: 14 March 2019
Please cite this article as: G. Yang, Z. Wu, D. Yang, S. Gai, M. Xu, X. Sun, P. Yang, Tunable multicolor and white emission NaLuF4:Yb, Nd, Ln (Ln = Er, Tm, Er/Tm) microstructures, Solid State Sciences (2019), doi: https://doi.org/10.1016/j.solidstatesciences.2019.03.010. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Masson SAS.
Tunable
multicolor
and
white
emission
NaLuF4:Yb, Nd, Ln (Ln = Er, Tm, Er/Tm) microstructures Guixin Yang*1, Zhenyu Wu*3, Dan Yang2, Shili Gai*2, Mengshu Xu2, Xiaojun Sun1, and Piaoping Yang *2
1 College of Chemical and Environmental Engineering, Harbin University of Science and Technology , Harbin, 150040, P. R. China. E-mail: [email protected] 2 Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Material Science and Chemical Engineering , Harbin Engineering
University
[email protected]
,
Harbin,
150001,
P.
R.
China.
E-mail:
[email protected]
3 Harbin Marine Boiler&Turbine Research Institute, Harbin, 150078, P. R. China. E-mail:[email protected]
*
Corresponding author: Fax: +86 431 86598041.
E-mail: [email protected] (P. Yang)
1
ABSTRACT A facile and surfactant-free molten salt method has been proposed to prepare a well-defined one-dimensional NaLuF4:Yb3+,Nd3+,Er3+,Tm3+ nanorods for the first time. It is found that by properly tuning the sensitizer (Nd3+) concentration in the host matrix upon 980 nm laser diode (LD) excitation, white up-conversion (UC) emission was achieved. Also, by doping Yb3+/Er3+/Tm3+/Nd3+ in NaLuF4 the relative intensities of different emissions can be precisely adjusted in a broad range. Consequently, by appropriately controling the emission intensity balance of blue, green and red basic colors in multicolor UC emissions, a strong white light can be realized in NaLuF4:Yb3+, Er3+,Tm3+,Nd3+ structures. UC mechanisms were analyzed in detail based on the emission spectra. The as-synthesized abundant luminescence colors in a wide region contribute themselves great potential applications. Furthermore, by manipulating the sensitizer concentration the paper provides an effective and facile method to gain a desired color.
Keywords: Upconversion, Nd-doping , sensitizer, luminescence
2
1. Introduction In recent years, lanthanide ions (Ln3+) doped up-conversion (UC) nanoparticles (NPs)[1-8] have been extensively investigated because of their unique optical properties, such as long luminescent lifetimes (micro- to milli-seconds), sharp emission bands, high penetration, low auto-fluorescence, low toxicity as well as high signal-to-noise ratio, which make them potential applications in displays, solar cells[9], biological imaging[10], phototherapy[11,12] and anti-counterfeiting[2,13]. Among all rare earth ions, Lu3+ for trivalent lanthanide (Ln3+) dopants’ due to the intensity-borrowing mechanism mixing the 4f and 5d orbital’s of the Ln3+ ions via the lattice valence band level, as a kind of colorless ion with optical inertia, is very suitable for using as an optical material[14-19]. Moreover, by influencing on the emitters’ electronic population life time, Lu3+ can remarkably tune the luminescent properties. At the same time, Lu3+ can absorb the X-ray and exhibit CT imaging. Therefore, Lu-based crystals, such as NaLuF4 can be widely used as a unique host material for up conversion luminescence [16, 20-22]. By now, many techniques have been used to synthesize those nano-structures, such as solid-state combinatorial chemistry method, sol-gel route chemical vapor synthesis and microwave assisted process. Besides, hydrothermal /solvothermal method is also a promising technique to develop some special nano-/microstructures which might be difficult or impossible to directly synthesizing in atmospheric pressure. The high temperature thermal decomposition method is easy to synthesize nanoparticles with super small size but usually release toxic substances to 3
environment [23-26]. Sol-gel route has many advantages such as low cost and good repeatability, but has the disadvantages of poor size uniformity [27]. Accordingly, the molten-salt growth method is a much better choice for synthesizing nanoparticles largely and greenly [28, 29]. By comparing with other experimental procedure such as co-precipitation method, molten salt synthesis method can ensure the oxidation state of rare earth metals ions and benefit for the formation of relatively fine and small particles with good luminescence performances. The molten salt method is used for synthesizing target crystals, their precursors are liquid phase medium formed by molten salt after the reaction temperature is up to the melting point of the salts. Benefiting from the incorporation of salt medium, the diffusion speeds of reacting components could be expedited, the reaction time and temperature could be expedited, the reaction time and temperature could reduced as well. Therefore, the molten salt method is considered as one of the most versatile, cost-effective and simplest approaches to obtain chemically purified, crystalline, single-phase with little residual impurities as compared with conventional solid-state reactions. Recently, many inorganic compounds have been synthesized through molten salt method, such as NaZnPO4 [30], and Tb3+-doped Ca2P2O7 [31, 32] etc. In present work, we report for the first time the preparation of uniformed NaLuF4:Ln (Ln = Yb3+,Er3+,Tm3+,Nd3+) nanorod through molten-salt method with high dispersity. We controlled the doping concentration of Yb3+, Er3+ and Tm3+ to achieve the siphonate morphology and white-light-emitting. On the other hand, we 4
investigate NaLuF4 nanocrystals by doping with different concentration of Nd3+. These doped NaLuF4 superstructures display strong UC emissions. The result indicates that this simple molten-salt method is an effective way for the synthesizing of NaLuF4 phosphors. Furthermore, the special structural geometry and excellent luminescent properties of as-prepared NaLuF4:Ln nanocrystals, together with mass production, low-cost, environmentally friendly and convenient procedure method, will endow this luminescent structure potential to serve as biomedical candidates, and display devices and solid-state lasers.
2. Experimental section 2.1. Reagents and materials. All the aforementioned chemical reagents used in this experiment are of analytical grade and received without further purification, including urea, concentrated HNO3 (Beijing Chemical including urea, concentrated HNO3 (Beijing Chemical Corporation, 69% Wt). Lu(NO3)3, NaF, NaNO3, and KNO3 (purity≥ 99.0%)were purchase analytical grade and received without further purification, including urea, concentrated HNO3 (Beijing Chemical from sinopharm Chemical Reagent Co., Ltd (China). Yb(NO3)3, Er(NO3)3, and Tm(NO3)3 (purity≥ 99.0%) were prepared by dissolving the corresponding Yb2O3, Er2O3 and Tm2O3 (99.99%, purchased from Changchun Applied Chemistry Science and Technology Limited, China) in HNO3 solution at elevated temperature from Changchun Applied Chemistry Science and Technology Limited, China) in HNO3 solution at elevated temperature followed by evaporating superfluous HNO3 and the under vacuum. 5
2.2. Synthesis Synthesis of NaLuF4 nanocrystals. In a typical process for the synthesis of hexagonal NaLuF4, stoichiometric Lu(NO3)3, NaF, NaNO3, KNO3 with molar ratio of 1: 4: 50: 25 were thoroughly mixed with appropriate amount of ethanol in an agate mort and ground for 30 min. This mixture was then transferred into an alumina and heated at 350
for different
reaction time. After cool down to the room temperature, the as-annealed samples were washed with demonized water, and subsequently dried at 100
overnight. Hexagonal
NaLuF4:Yb3+, Er3+, Tm3+, Nd3+ were prepared in a similar procedure by adding corresponding Yb(NO3)3, Er(NO3)3, Tm(NO3)3, Nd(NO3)3 into the precursor mixture. Notably, we can easily and routinely scale up this process to produce large amounts of NaLuF4:Ln phosphors.
3. Results and discussion 3.1. Phase identification and morphology of lutetium precursor Fig. 1 shows the XRD patterns of the as-synthesized NaLuF4:Yb3+, Er3+, Tm3+ as well as the standard data of pure β-NaLuF4 for comparison. As shown, all the characteristic diffraction peaks of the pattern is very sharp and strong, which may indicate a high crystallinity of the sample. However, on the basis of the Joint Committee on Powder Diffraction Standards (JCPDS No. 27-7026) reference database, a compound diffraction pattern can be found. Nevertheless, the diffraction peaks of the sample are quite similar to JCPDS No. 27-0726 in both their positions and relative intensities, which indicates the sample is directly indexed to the pure hexagonal NaLuF4 crystal. 6
The as-prepared NaLuF4:Yb3+,Er3+,Tm3+ crystals with pure hexagonal phase exhibit morphology of nanorod, as shown in Fig. 2. The SEM image in Fig. 2A reveals that β-NaLuF4:Yb3+, Er3+, Tm3+ consists of hollow and hexagonal rod morphologies. The SEM image in Fig. 2A reveals that the NaLuF4:Yb, Er, Tm consists of uniform hexagonal microtubes 2–3 µm in length and 300-500 nm in diameter.
It can be seen that the particles present the similar morphology and size
distribution. However, the size and morphology and size of the particles are not relatively uniform and regular. Although the aggregation of the particles is still observed through the molten salt method, the temperature is much lower than that of solid state reaction and the reaction period is much shorter. Therefore, this can save a lot of energy resource. In Fig. 2B, EDS shows a characteristic intensity profile of Na, Lu and F elements. As the low doping amount of Er and Tm, it is difficult to distinguish their energy spectrum, but the characteristic peaks in the up-conversion fluorescence spectra can prove the existence of these two elements. When Nd3+ was doped in NaLuF4:Yb3+,Er3+,Tm3+, the XRD of the new sample was changed. As shown in Fig. 3, in addition to the original hexagonal phase, the cubic NaLuF4 appeared which indicated that the crystal phase was changed by doping Nd3+. This is because the ion radius of Nd3+ is 141 pm which is larger than that of Lu3+(the radius is 84.89 pm), and the difference is obvious, so the transformation of the crystal phase is produced in the synthesis process. We also investigate the XRD patterns of Nd3+ doped samples with different concentrations. When the concentration of Nd3+ increased, the shape of the peak becomes disordered, which affect the change of the 7
crystallites becomes large. And the lowest Nd3+ concentration to induce such change is 5%. The as-prepared NaLuF4:Yb3+,Nd3+,Er3+,Tm3+ crystals exhibit nano-rod morphologies, which are shown in Fig. 4A. The EDS (Fig. 4B) confirms the presence of Na, Lu, Yb, Nd and F elements, which indicates that the Nd3+ has been successfully doped in the crystals. UC luminescence properties It is well acknowledged that rare earth (RE) fluorides (especially NaREF4 or REF3) are excellent host lattices for the luminescence of various lanthanide ions. To investigate the luminescent properties of as-synthesized nanorod bundles, NaLuF4 doped with different RE ions was designed and discussed. It is acknowledged that, when sensitized by Yb3+, Er3+ can emit high intensity UC luminescence in red and green wavelength range under the excitation of infrared light. Fig. 5A gives the UC spectrum of NaLuF4:Yb3+, Er3+. It can be seen that NaLuF4:Yb3+, Er3+ sample can emit the characteristic Er3+ transition bands centered at 411 nm (from 2H9/2 to 4I15/2 ), 521 nm (from 2H11/2 to 4I15/2), 541 nm (from 4S2/3 4
to
I15/2), and 655 nm (from 4F9/2 to 4I15/2). It should point out that the observation of 411
nm emission indicates the high UC efficiency of as-prepared NaLuF4 host. Because generally, the 411 nm emission could not be observed due to the low efficiency of three or four-photon UC and strong scattering of host lattices. In Fig. 5B for NaLuF4:Yb,Tm nanorods, the three emission bands at around 475 nm, 655 nm and 700 nm can be assigned to the thermalized from 1D2 to 3F4, from 1G4 to 3H6, from 1G4 to 3F4, and from 3F3 to 3H6 transition of Tm3+, respectively. For NaLuF4:Yb3+, Er3+,
8
Tm3+ nanorods in Fig. 5C, the Er3+ ions generate a very strong red transition (from 1
G4 to 3F4) at 648 nm. Moreover, we can also find that relative emission intensities of
the red, green and blue colors. The respective CIE (commission Internationale de I’Eclairage 1931 chromaticity) coordinates for UC emission spectra of NaLuF4:Yb,Er, NaLuF4:Yb,Tm and NaLuF4:Yb,Er,Tm products are given in the Fig. 5D. Furthermore, there is a simple regularity to each phosphor, the CIE chromaticity values of different doping level samples are arranged approximately in line, which would be a date base for further study in the color parameters of this kind of phosphors. The CIE chromaticity coordinates (x, y) of NaLuF4:33%Yb3+, x%Er3+,2%Tm3+ (x = 0, 1, 1.5, 2) with different Er3+ concentration are summarized in Table 1. As illustrated, by changing of Er3+ doping concentration the chromaticity coordinates changes, and the luminescent colors can be altered in a wide scope (Fig. 6). And the luminescent colors were changed from blue to white, then to yellow. Specially, when the doping concentration of Er3+ was 1%, the output color becomes white. Moreover, the precise control of the intensity balance for blue, green and red emissions by co-doping Yb3+/ Er3+/Tm3+, the output color change from blue to yellow basic colors by simply tuning the Er3+ doping concentration may also offer a simple and efficient method to obtain a desired color. We next examined the emission intensity of NaLuF4:Yb3+, Er3+, Nd3+ with different concentrations of Nd3+ dopants from 5% to 30%. As shown in Fig. 7A, the UCL intensity of the NaLuF4:Yb3+,Er3+,Nd3+ is affected by Nd3+ ions, in detail, decreased 9
upon increasing the concentration of Nd3+ from 5% to 30 mol% in the naked-core nanoparticles. And Fig. 7B gives the original UC spectra of NaLuF4:Yb3+, Er3+, Nd3+ with different doping concentrations of Nd3+(5% - 30%). It can be observed that all five NaLuF4:Yb3+, Er3+, Nd3+ samples can send out the symbolic Er3+ transition bands focus on
411, 521, 541 and 655 nm, which indicating that Er3+ successfully doped
into the NaLuF4 nanoparticles. As shown in Fig. 7C, the peak area ratio of the red area (from 4F9/2 to 4I15/2) to the green area (from2H11/2，4S3/2 to 4I15/2) tunes from 1.75 to 2.71 with the changing of Nd3+ concentration. When the doped Nd3+ concentration is increased to 30 – 40%, the luminescent intensity reduced. This phenomenon is resulted from energy back-transfer from Er3+ to Nd3+ which produces the energy quenching. While the doped Nd3+ concentration increased the degree of quenching, which lead to the decrease of emission intensity. Table 2 shows the effect of different doped Nd3+ on the calculated CIE chromaticity coordinates of NaLuF4:33%Yb3+,1%Er3+,x%Nd3+. As shown, the chromaticity coordinates alter with the tune of Nd3+ doping concentration, and the luminescent colors can be changed in a wide scope. Fig. 5D illustrated the tunable color region for Yb3+ doped NaLuF4:Yb3+, Er3+. All kinds of luminescence colors and wide color area of the NaLuF4:Yb3+, Er3+, Tm3+ samples under 980 nm LD excitation devote themselves great potential applications in a variety of areas. More importantly, the accurate command of the intensity balance for the red, white and yellow colors by simply changing the Yb3+ doping concentration may also offering an effective and convenient method to obtain a perfect color. 10
The NaLuF4 phosphors co-doped with 33%Yb3+, 2%Tm3+ and x% Nd3+ ions (x = 5, 10, 20, and 30) were also prepared, and transitions of Tm3+ (from 1D2 to 3F4 at 450 nm, and from 1G4 to 3H6 at 480 nm ions) were found. With an increasing in the doped Nd3+ concentration, the relative intensities of the blue and red bands altered. Fig. 8B illustrates the original UC luminescence spectra excited by 980 nm LD. It can be seen that all five NaLuF4:Yb3+, Tm3+, Nd3+ samples can emit characteristic Tm3+ transition bands centered at 475, 644 and 700 nm, which indicating that Tm3+successfully doped into the NaLuF4 nanoparticles. As illustrated in Fig. 7C, the peak area ratio of the red area becomes obvious by changing of Nd3+ concentration. When the doped Nd3+ concentration is 5 - 10%, the blue emission is most powerful emission color. While the doped Nd3+ concentration is changed to 20 - 30%, the variation trend of blue emission becomes obvious. Table 3 shows the effect of different doped Nd3+ on the calculated CIE chromaticity coordinates of NaLuF4:33%Yb3+,2%Tm3+,x%Nd3+. As shown, by altering the Nd3+ doping concentration the chromaticity coordinates changes, and the luminescent colors can be changed in a wide range. Fig. 8D illustrated the tunable color region for Nd3+ doped NaLuF4:Yb3+, Tm3+, which is marked by the solid-lined. These abundant luminescence colors and wide color area of the NaLuF4:Yb3+, Tm3+, Nd3+ phosphors under 980 nm LD excitation devote themselves great potential applications in a variety of areas. More importantly, by simply adjusting the Nd3+ doping concentration may also provide a convenient and effective method to obtain a
11
perfect color, the precise command of the intensity balance for the green, red and blue colors. We finally examined the emission intensity of NaLuF4:Yb3+,Er3+,Tm3+,Nd3+ with different concentration of Nd3+ dopants from 5% to 30%. As shown in Fig. 9A, the UCL intensity of NaLuF4:Yb3+, Er3+, Tm3+, Nd3+ which is affected by the Nd3+ ions decreased upon increasing the concentration of Nd3+ from 5 to 30 mol% in the naked-core nanoparticles. From Fig.9 A we can see the blue (450 and 480 nm) green (520 and 540 nm), and red (655 nm) emissions. Compared with the UC spectra
of
NaLuF4:33%Yb3+,1%Er3+,
x%Nd3+
(Fig.7A)
and
NaLuF4:33%Yb3+,2%Tm3+,x% Nd3+(Fig.8A) (x = 5, 10, 20, 30), it is easy to assign the origins of the observed emission bands. The blue emissions centered at 450 and 480 nm are generated from the electronic transitions of Tm3+(1D2→3F4, and 1G4→3H6). The green and red emissions originate frm the electronic transion of Er3+ ions at 520 (2H11/2→4I15/2), 540 (4S3/2→4I15/2) and 655(4F9/2→4I15/2). It is noted that Tm3+ions also generate a very weak red transion of 1G4→3F4 at 648 nm.[33-35] Which may be covered by red emission of Er3+ ion. Moreover, we can also find that the relative emission intensities of red, green and blue colors change with Nd3+ concentrations. And Fig. 9B shows the original UC luminescence spectra of NaLuF4:Yb3+, Er3+,Tm3+, Nd3+ with different concentrations of Nd3+ (5% - 30%) excited by 980 nm LD. It can be seen that all five NaLuF4:Yb3+,Er3+,Tm3+,Nd3+ samples can emit characteristic Er3+ and Tm3+ transition bands which indicating that both the ions were successfully doped into the NaLuF4 12
nanoparticles. As illustrated in Fig. 9C, the peak area ratio of the green area becomes obvious with the changing of Nd3+ concentration. When the doped Nd3+ concentration is 5 –10%, the green emission is the strongest emission color. While the doped Nd3+ concentration is changed to 20 - 30%, the variation trend of green emission becomes obvious. Table 4 shows the change of different doped Nd3+ on the calculated CIE chromaticity coordinates of NaLuF4:33%Yb3+,1%Er3+,2%Tm3+,x%Nd3+. As shown, the chromaticity coordinates altered with the change of Nd3+ doping concentration, and the emitting colors can be changed in a wide range. Fig. 9D illustrates the tunable color scope for Nd3+ doped NaLuF4:Yb3+, Er3+, Tm3+. These abundant luminescence colors and wide color region of the NaLuF4:Yb3+, Er3+, Tm3+, Nd3+ phosphors under 980 nm LD excitation devotes themselves many potential applications in a variety areas. More importantly, the precise control of the intensity balance for the green, blue and red colors by simply changing the Nd3+ doping concentration may also offer a convenient and efficient way to obtain a desired color.
4. Conclusions In conclusion, NaLuF4 nanorods have been firstly prepared through a simple one-pot molten salt procedure. The phase and morphology were well discussed. The UC luminescence properties of NaLuF4 crystals doped with different RE ions (Yb3+/Er3+/Nd3+, Yb3+/Tm3+/Nd3+ , Yb3+/Er3+/Tm3+/Nd3+) were researched under 980 nm LD excitation. By adjusting the Nd3+ doping concentration, the relative emission
13
colors intensities can be precisely commanded resulting in a variety of visible emissions. More importantly, by controlling the emission intensity balance for the three green, blue, and red basic colors, white light luminescence are gained in the NaLuF4:Yb3+, Er3+,Tm3+, Nd3+ sample. The consequence indicate a general procedure for the progress of highly-efficient luminescent UC phosphors in a wide color range, which have many potential applications in a variety of areas
Acknowledgments Financial support from National Natural Science Foundation of China (NSFC 51702070, 21676066), Natural Science Foundation of Heilongjiang Province (QC2017006), Harbin Science and Technology Youth Reserve Talent Project (2017RAQXJ077), 2017T00228),
and
China
Postdoctoral
Heilongjiang
Science
Postdoctoral
Foundation
(2016M600241,
Foundation(LBH-Z16050),
Fundamental Research Funds for the Harbin Engineering University are greatly acknowledged.
References [1] L. T. Liu, L. H. Cheng, B. J. Chen, J. Y. Shang, X. H. Qi, Y. A. Zhu and R. N. Hua, Dependence of optical temperature sensing and photo-thermal conversion on particle size and excitation wavelength in β-NaYF4:Yb3+, Er3+ nanoparticles, J. Alloys Compd., 741, 2018, 927-936. [2] Q. Luo, X. S. Deng, W. H. Chen, H. Guo, O. Y. Wei, X. H. Chen and S. M. Huang, Enhancing upconversion from NaYF4:Yb,Er@NaYF4 core–shell 14
nanoparticles assembled on metallic nanostructures, J. Nanosci Nanotechno., 18, 2018, 5063-5073. [3] C. Zhu, W. Y. Zhou, J. J. Fang, Y. R. Ni, L. Fang, C. H. Lu, Z. Z. Xu and Z. T. Kang, Improved upconversion efficiency and thermal stability of NaYF4@SiO2 photonic crystal film, J. Alloys Compd., 741, 2018, 337-347. [4]
Y. Gao, J. Z. Feng, C. Shi, M. M. Fan, GuiyanZhao, Y. F. Bi, Y. G. Sun, F. Ding and Z. H. Xu,
Highly uniform hollow GdF3 ellipsoids: controllable synthesis,
characterization and
up-conversion luminescence properties, J. Nanosci
Nanotechno., 18, 2018, 5822-5827. [5] P. Du, X. Y. Huang and J. S. Yu, Facile synthesis of bifunctional Eu3+-activated NaBiF4 red-emitting nanoparticles for simultaneous white light-emitting diodes and field emission displays, Chem. Eng. J., 337, 2018, 91-100. [6] X. Q. Zhao, H. Suo, Z. Y. Zhang and C. F. Guo, Cross-relaxation and non-steady-state processes induced up-conversion color modulation in Gd2O3: Ln3+/Er3+ (Ln = Tm, Ho), Dyes Pigments, 151, 2018, 335-341. [7] D. den Engelsen, G. R. Fern, T. G. Ireland and J. Silver, Reassignment of electronic transitions in the laser-activated spectrum of nanocrystalline Y2O3:Er3+, J. Lumin., 196, 2018, 337-346. [8] Z. A. S. Mahraz, M. R. Sahar and S. K. Ghoshal, Near-infrared up-conversion emission from erbium ions doped amorphous tellurite media: Judd-Ofelt evaluation, J. Alloys Compd., , 740, 2018, 617-625. [9] Z. H. Zhao, X. Zhang, J. M. Fan, D. F. Xue, B. Zhang and S. Yin, 15
N-TiO2/g-C3N4/Up-conversion phosphor composites for the full-spectrum light-responsive deNO x photocatalysis, J. Mater. Sci., 53, 2018,7266-7278. [10] R. Lv, D. Yang, P. Yang, J. Xu, F. He, S. Gai, C. Li, Y. Dai, G. Yang and J. Lin, Integration of upconversion nanoparticles and ultrathin black phosphorus for efficient photodynamic theranostics under 808 nm near-infrared light irradiation, Chem. Mater., 28 (13), 2016, 4724-4734. [11] H. Bi, Y. Dai, R. Lv, C. Zhong, F. He, S. Gai, A. Gulzar, G. Yang and P. Yang, Doxorubicin-conjugated CuS nanoparticles for efficient synergistic therapy triggered by near-infrared light, Dalton. T., 45, 2016, 5101-5110. [12] L. Feng, F. He, B. Liu, G. Yang, S. Gai, P. Yang, C. Li, Y. Dai, R. Lv and J. Lin, g-C3N4 coated upconversion nanoparticles for 808 nm near-infrared light triggered
phototherapy
and
multiple
imaging,
Chem.
Mater.,28,
2016,7935-7946. [13] J. F. Tang, Y. W. Huang, M. J. Sun, J. Gou, Y. Zhang, G. N. Li, Y. C. Kang, J. Yang and Z. H. Xiao, Spectroscopic characterization and temperature-dependent upconversion behavior of Er3+ and Yb3+ co-doped zinc phosphate glass, J. Lumin., 197, 2018,, 153-158. [14] N. Niu, P. P. Yang, F. He, X. Zhang, S. L. Gai, C. X. Li and J. Lin, Tunable multicolor and bright white emission of one-dimensional NaLuF4:Yb3+,Ln3+ (Ln = Er, Tm, Ho, Er/Tm, Tm/Ho) microstructures, J. Mater. Chem., 22, 2012, 10889-10899. [15] A. Bagheri, H. Arandiyan, C. Boyer, M. Lim, Lanthanide-doped upconversion 16
nanoparticles: emerging intelligent light-activated drug delivery systems, Adv. Sci. 3 , 2016. [16]T. S. Yang, Y. M. Wang, H. Gao, Q. Liu and K. Y. Zhang, Eur. RGD-Peptide-Modified
NaLuF4:Yb,Er
nanocrystals
for
upconversion-luminescence-targeted tumor-cell imaging, J. Inorg. Chem., 44, 2017, 5169-5175. [17] M. Y. Ding, D. Q. Chen, C. H. Lu, J. H. Xi, Z. G. Ji and Z. Z. Xu, Hydrothermal synthesis,
energy
transfer
and
luminescent
properties
of
β-NaLuF4:Ce3+/Gd3+/Sm3+ microcrystals, J. Lumin., 186, 2017, 109-116. [18] L. L. Tong, X. P. Li, R. N. Hua, L. H. Cheng, J. S. Sun, J. S. Zhang, S. Xu, H. Zheng, Y. Q. Zhang and B. J. Chen, Optical temperature sensing properties of Yb3+/Tm3+ co-doped NaLuF4 crystals , Curr. Appl. Phys. , 17, 2017, 999-1004. [19] A. Xie and C. Y. Cao, Synthesis and Optical Properties of Yb3 +/Er3 +, Yb3 +/Tm3 +, Eu3 + Doped NaLuF4, Na5Lu9F32, KLu3F10, and KLu2F7, Nanosci. Nanotech. Let., 9, 2017,305-309. [20] H. Y. Lu, H. Y. Hao, H. M. Zhu, G. Shi, Q. D. Fan, Y. L. Song, Y. X. Wang and X. R. Zhang, Enhancing temperature sensing behavior of NaLuF4:Yb3+/Er3+via incorporation of Mn2+ ions resulting in a closed energy transfer, J. Alloys Compd., 728, 2017, 971-975. [21] Y. Liu, N. Kang, J. Lv, Z. Zhou, Q. Zhao, L. Ma, Z. Chen, L. Ren, L. Nie, Deep photoacoustic/luminescence/magnetic resonance multimodal imaging in living subjects using high-efficiency upconversion nanocomposites, Adv. Mater. 17
28 ,2016, 6411–6419. [22] D. P. Yang, C. Cao, W. Feng, C. H. Huang and F. Y. Li, Synthesis of NaYF4:Nd@NaLuF4@SiO2@PS Colloids for Fluorescence Imaging in the Second Biological Window, J. Rare Earth., 36, 2018, 113-118. [23] X. B. Li, S. L. Gai, C. X. Li, D. Wang, N. Niu, F. He and P. P. Yang, Monodisperse lanthanide fluoride nanocrystals: synthesis and luminescent properties, Inorg. Chem., 51, 2012, 3963-3971. [24] S. L. Gai, G. X. Yang, X. B. Li, C. X. Li, Y. L. Dai, F. He and P. P. Yang, Facile synthesis and up-conversion properties of monodisperse rare earth fluoride nanocrystals, Dalton. T., 41, 2012,
11716-11724.
[25] S. L. Gai, P. P. Yang, X. B. Li, C. X. Li, D. Wang, Y. L. Dai and J. Lin, Monodisperse CeF3, CeF3:Tb3+, and CeF3:Tb3+@LaF3 core/shell nanocrystals: synthesis and luminescent properties, J. Mater. Chem., 21, 2011, 14610-14615. [26] C. N. Zhong, P. A. P. Yang, X. B. Li, C. X. Li, D. Wang, S. L. Gai and J. Lin, Monodisperse bifunctional Fe3O4@NaGdF4:Yb/Er@NaGdF4:Yb/Er core–shell nanoparticles, Rsc Adv., 2, 2012, 3194-3197. [27] K. K. Patankar, D. M. Ghone, V. L. Mathe and S. D. Kaushik, Structural and physical property study of sol–gel synthesized CoFe2−xHoxO4 Nano Ferrites, J. Magn. Magn. Mater., 454, 2018, 71-77. [28] J. Fu, Y. D. Hou, M. P. Zheng and M. K. Zhu, Comparative study of dielectric properties of the PVDF composites filled with spherical and rod-like BaTiO3 derived by molten salt synthesis method, J. Mater. Sci., 53, 2018, 7233-7248. 18
[29] L. Tian, J. Y. Li, F. Liang, J. K. Wang, S. S. Li, H. J. Zhang and S. W. Zhang, Molten salt synthesis of tetragonal carbon nitride hollow tubes and their application for removal of pollutants from wastewater,
Appl. Catalysis
B-Environmental, 225, 2018, 307-313. [30] L. Mukhopadhyay, V. K. Rai, R. Bokolia, K. Sreenivas, 980 nm excited Er3+/Yb3+ /Li3+ /Ba2+ : NaZnPO4 upconverting phosphors in optical thermometry , J. Lumin., 187, 2017, 368-377. [31] L. Mukhopadhyay, V. K. Rai, Upconversion based near white light emission, intrinsic
optical
bistability
and
temperature
sensing
in
Er3+/Tm3+
/Yb3+/Li+ :NaZnPO 4 phosphors, New J. Chem. 41, 2017, 7650-7661. [32] Y. Tian, Y. H. Fang, B. N. Tian, C. Cui, P. Huang, L. Wang, H. Y Jia, B. J. Chen, Molten salt synthesis, energy transfer, and temperature quenching fluorescence of green-emitting β-Ca2P2O7:Tb
3+
phosphors, J. Mater. Sci., 50, 2015,
6060-6065. [33] M. C. Wong, C. Li, M. K. Tsang, Y. Zhang, J. H. Hao, Magnetic-Induced Luminescence from Flexible Composite Laminates by Coupling Magnetic Field to Piezophotonic Effect, Adv. Mater., 27, 2015, 4488-4495. [34] G. X. Bai, S. G. Yuan, Y. D. Zhao, Z. B. Yang, S. Y. Choi, Y. Chai, S. F. Yu, S. P. Lau, J. H. Hao, 2D Layered Materials of Rare-Earth Er-Doped MoS 2 with NIR-to-NIR Down- and Up-Conversion Photoluminescence, Adv. Mater., 28, 2016, 7472-7477. [35] M. C. Wong, C. Li, G. G. Bai, L. B. Huang, J. H. Hao, Temporal and Remote 19
Tuning of Piezophotonic-Effect-Induced Luminescence and Color Gamut via Modulating Magnetic Field, Adv. Mater., 29, 2017, 170945.
Fig. 1 XRD patterns of NaLuF4:Yb, Er, Tm prepared at 350℃ for reaction time of 3 h, and the standard data of hexagonal β-NaLuF4 (JCPDS No. 27-0726).
Fig. 2 (A) Low magnification SEM images and (B) EDS of NaLuF4:Yb,Er,Tm.
20
Fig.3 XRD patterns of NaLuF4:Yb3+,Nd3+,Er3+,Tm3+ prepared at 350℃ and the standard data of cubic α-NaLuF4 (JCPDS No. 27-0725) and hexagonal β-NaLuF4 (JCPDS No. 27-0276).
Fig. 4 (A) Low magnification SEM images and (B) EDS of NaLuF4:Yb,Er,Tm,Nd
21
Fig.5
(A)
The
UC
luminescence
properties
of
NaLuF4:Yb3+,Er3+,
NaLuF4:Yb3+,Tm3+, and (C) the CIE chromaticity of the three crystals.
22
(B)
Fig.6 the CIE chromaticity of NaLuF4:33%Yb3+, x%Er3+, 2%Tm3+.
Fig.7 (A) Comparable and (B) original UC luminescence properties of NaLuF4:33%Yb3+,1%Er3+,x%Nd3+ with different Nd3+ concentrations. (C) Peak area ratio
of
red
and
green
emissions.
(D)
The
CIE
chromaticity
NaLuF4:33%Yb3+,1%Er3+,x%Nd3+ showing the tunable color region. 23
of
Fig.8 (A) Comparable and (B) original UC luminescence properties of NaLuF4:33%Yb3+,2%Tm3+, x%Nd3+. (C) Peak area ratio of red, green and blue emissions. (D) The CIE chromaticity of NaLuF4:33%Yb3+, 2%Tm3+,x%Nd3+ showing the tunable color region of Yb3+/Tm3+/Nd3+ doped crystals.
24
Fig. 9 (A) Comparable and (B) original UC luminescence properties of NaLuF4:33%Yb3+,2%Er3+,1%Tm3+,x%Nd3+ with different Nd3+ doping concentration. (C) Peak area ratio of blue, green and red emissions. (D) The CIE chromaticity of NaLuF4:Yb3+,Er3+,Tm3+,x%Nd3+ doped crystals.
Table
1
The
calculated
CIE
chromaticity
coordinates
NaLuF4:33%Yb3+,x%Er3+,2%Tm3+ samples. samples NaLuF4:33%Yb3+,0%Er3+,2%Tm3+
x 0.2271
y 0.1162
NaLuF4:33%Yb3+,1%Er3+,2%Tm3+
0.3050
0.2670
NaLuF4:33%Yb3+,1.5%Er3+,2%Tm3+ 0.3352
0.4297
NaLuF4:33%Yb3+,2%Er3+,2%Tm3+ 25
0.3549
0.4757
(x,
y)
of
Table
2
The
calculated
CIE
chromaticity
coordinates
(x,
y)
of
(x,
y)
of
(x,
y)
of
NaLuF4:33%Yb3+,1%Er3+,x%Nd3+ samples.
Table
3
samples NaLuF4:33%Yb3+,1%Er3+,5%Nd3+
x 0.3584
y 0.6007
NaLuF4:33%Yb3+,1%Er3+,10%Nd3+
0.3628
0.5919
NaLuF4:33%Yb3+,1%Er3+,20%Nd3+
0.3721
0.5754
NaLuF4:33%Yb3+,1%Er3+,30%Nd3+
0.3989
0.5190
The
calculated
CIE
Chromaticity
coordinates
NaLuF4:33%Yb3+,2%Tm3+
Table
4
samples NaLuF4:33%Yb3+,2%Tm3+,5%Nd3+
x 0.1529
y 0.0753
NaLuF4:33%Yb3+,2%Tm3+,10%Nd3+
0.1584
0.0915
NaLuF4:33%Yb3+,2%Tm3+,20%Nd3+
0.1962
0.1539
NaLuF4:33%Yb3+,2%Tm3+,30%Nd3+
0.2638
0.2604
The
calculated
CIE
chromaticity
coordinates
NaLuF4:33%Yb3+,1%Er3+,2%Tm3+,x%Nd3+ samples NaLuF4:33%Yb ,1%Er3+,2%Tm3+,5%Nd3+
x 0.2455
y 0.4958
NaLuF4:33%Yb3+,1%Er3+,2%Tm3+,10%Nd3+
0.2660
0.5625
NaLuF4:33%Yb3+,1%Er3+,2%Tm3+,20%Nd3+
0.2844
0.5243
NaLuF4:33%Yb3+,1%Er,2%Tm3+,30%Nd3+
0.2891
0.4363
3+
26
1.
In this study, we firstly proposed a strategy to preparing one-dimensional NaLuF4:Yb3+,Nd3+, Er3+, Tm3+ nanorods by a surfactant-free molten salt method .
2.
Upon 980 nm laser diode (LD) excitation, white up-conversion light was successfully achieved by properly tuning the sensitizer (Nd3+) concentration in the host matrix.
S1293-2558(18)31271-8
DOI:
https://doi.org/10.1016/j.solidstatesciences.2019.03.010
Reference:
SSSCIE 5860
To appear in:
Solid State Sciences
Received Date: 28 November 2018 Revised Date:
7 March 2019
Accepted Date: 14 March 2019
Please cite this article as: G. Yang, Z. Wu, D. Yang, S. Gai, M. Xu, X. Sun, P. Yang, Tunable multicolor and white emission NaLuF4:Yb, Nd, Ln (Ln = Er, Tm, Er/Tm) microstructures, Solid State Sciences (2019), doi: https://doi.org/10.1016/j.solidstatesciences.2019.03.010. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Masson SAS.
Tunable
multicolor
and
white
emission
NaLuF4:Yb, Nd, Ln (Ln = Er, Tm, Er/Tm) microstructures Guixin Yang*1, Zhenyu Wu*3, Dan Yang2, Shili Gai*2, Mengshu Xu2, Xiaojun Sun1, and Piaoping Yang *2
1 College of Chemical and Environmental Engineering, Harbin University of Science and Technology , Harbin, 150040, P. R. China. E-mail: [email protected] 2 Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Material Science and Chemical Engineering , Harbin Engineering
University
[email protected]
,
Harbin,
150001,
P.
R.
China.
E-mail:
[email protected]
3 Harbin Marine Boiler&Turbine Research Institute, Harbin, 150078, P. R. China. E-mail:[email protected]
*
Corresponding author: Fax: +86 431 86598041.
E-mail: [email protected] (P. Yang)
1
ABSTRACT A facile and surfactant-free molten salt method has been proposed to prepare a well-defined one-dimensional NaLuF4:Yb3+,Nd3+,Er3+,Tm3+ nanorods for the first time. It is found that by properly tuning the sensitizer (Nd3+) concentration in the host matrix upon 980 nm laser diode (LD) excitation, white up-conversion (UC) emission was achieved. Also, by doping Yb3+/Er3+/Tm3+/Nd3+ in NaLuF4 the relative intensities of different emissions can be precisely adjusted in a broad range. Consequently, by appropriately controling the emission intensity balance of blue, green and red basic colors in multicolor UC emissions, a strong white light can be realized in NaLuF4:Yb3+, Er3+,Tm3+,Nd3+ structures. UC mechanisms were analyzed in detail based on the emission spectra. The as-synthesized abundant luminescence colors in a wide region contribute themselves great potential applications. Furthermore, by manipulating the sensitizer concentration the paper provides an effective and facile method to gain a desired color.
Keywords: Upconversion, Nd-doping , sensitizer, luminescence
2
1. Introduction In recent years, lanthanide ions (Ln3+) doped up-conversion (UC) nanoparticles (NPs)[1-8] have been extensively investigated because of their unique optical properties, such as long luminescent lifetimes (micro- to milli-seconds), sharp emission bands, high penetration, low auto-fluorescence, low toxicity as well as high signal-to-noise ratio, which make them potential applications in displays, solar cells[9], biological imaging[10], phototherapy[11,12] and anti-counterfeiting[2,13]. Among all rare earth ions, Lu3+ for trivalent lanthanide (Ln3+) dopants’ due to the intensity-borrowing mechanism mixing the 4f and 5d orbital’s of the Ln3+ ions via the lattice valence band level, as a kind of colorless ion with optical inertia, is very suitable for using as an optical material[14-19]. Moreover, by influencing on the emitters’ electronic population life time, Lu3+ can remarkably tune the luminescent properties. At the same time, Lu3+ can absorb the X-ray and exhibit CT imaging. Therefore, Lu-based crystals, such as NaLuF4 can be widely used as a unique host material for up conversion luminescence [16, 20-22]. By now, many techniques have been used to synthesize those nano-structures, such as solid-state combinatorial chemistry method, sol-gel route chemical vapor synthesis and microwave assisted process. Besides, hydrothermal /solvothermal method is also a promising technique to develop some special nano-/microstructures which might be difficult or impossible to directly synthesizing in atmospheric pressure. The high temperature thermal decomposition method is easy to synthesize nanoparticles with super small size but usually release toxic substances to 3
environment [23-26]. Sol-gel route has many advantages such as low cost and good repeatability, but has the disadvantages of poor size uniformity [27]. Accordingly, the molten-salt growth method is a much better choice for synthesizing nanoparticles largely and greenly [28, 29]. By comparing with other experimental procedure such as co-precipitation method, molten salt synthesis method can ensure the oxidation state of rare earth metals ions and benefit for the formation of relatively fine and small particles with good luminescence performances. The molten salt method is used for synthesizing target crystals, their precursors are liquid phase medium formed by molten salt after the reaction temperature is up to the melting point of the salts. Benefiting from the incorporation of salt medium, the diffusion speeds of reacting components could be expedited, the reaction time and temperature could be expedited, the reaction time and temperature could reduced as well. Therefore, the molten salt method is considered as one of the most versatile, cost-effective and simplest approaches to obtain chemically purified, crystalline, single-phase with little residual impurities as compared with conventional solid-state reactions. Recently, many inorganic compounds have been synthesized through molten salt method, such as NaZnPO4 [30], and Tb3+-doped Ca2P2O7 [31, 32] etc. In present work, we report for the first time the preparation of uniformed NaLuF4:Ln (Ln = Yb3+,Er3+,Tm3+,Nd3+) nanorod through molten-salt method with high dispersity. We controlled the doping concentration of Yb3+, Er3+ and Tm3+ to achieve the siphonate morphology and white-light-emitting. On the other hand, we 4
investigate NaLuF4 nanocrystals by doping with different concentration of Nd3+. These doped NaLuF4 superstructures display strong UC emissions. The result indicates that this simple molten-salt method is an effective way for the synthesizing of NaLuF4 phosphors. Furthermore, the special structural geometry and excellent luminescent properties of as-prepared NaLuF4:Ln nanocrystals, together with mass production, low-cost, environmentally friendly and convenient procedure method, will endow this luminescent structure potential to serve as biomedical candidates, and display devices and solid-state lasers.
2. Experimental section 2.1. Reagents and materials. All the aforementioned chemical reagents used in this experiment are of analytical grade and received without further purification, including urea, concentrated HNO3 (Beijing Chemical including urea, concentrated HNO3 (Beijing Chemical Corporation, 69% Wt). Lu(NO3)3, NaF, NaNO3, and KNO3 (purity≥ 99.0%)were purchase analytical grade and received without further purification, including urea, concentrated HNO3 (Beijing Chemical from sinopharm Chemical Reagent Co., Ltd (China). Yb(NO3)3, Er(NO3)3, and Tm(NO3)3 (purity≥ 99.0%) were prepared by dissolving the corresponding Yb2O3, Er2O3 and Tm2O3 (99.99%, purchased from Changchun Applied Chemistry Science and Technology Limited, China) in HNO3 solution at elevated temperature from Changchun Applied Chemistry Science and Technology Limited, China) in HNO3 solution at elevated temperature followed by evaporating superfluous HNO3 and the under vacuum. 5
2.2. Synthesis Synthesis of NaLuF4 nanocrystals. In a typical process for the synthesis of hexagonal NaLuF4, stoichiometric Lu(NO3)3, NaF, NaNO3, KNO3 with molar ratio of 1: 4: 50: 25 were thoroughly mixed with appropriate amount of ethanol in an agate mort and ground for 30 min. This mixture was then transferred into an alumina and heated at 350
for different
reaction time. After cool down to the room temperature, the as-annealed samples were washed with demonized water, and subsequently dried at 100
overnight. Hexagonal
NaLuF4:Yb3+, Er3+, Tm3+, Nd3+ were prepared in a similar procedure by adding corresponding Yb(NO3)3, Er(NO3)3, Tm(NO3)3, Nd(NO3)3 into the precursor mixture. Notably, we can easily and routinely scale up this process to produce large amounts of NaLuF4:Ln phosphors.
3. Results and discussion 3.1. Phase identification and morphology of lutetium precursor Fig. 1 shows the XRD patterns of the as-synthesized NaLuF4:Yb3+, Er3+, Tm3+ as well as the standard data of pure β-NaLuF4 for comparison. As shown, all the characteristic diffraction peaks of the pattern is very sharp and strong, which may indicate a high crystallinity of the sample. However, on the basis of the Joint Committee on Powder Diffraction Standards (JCPDS No. 27-7026) reference database, a compound diffraction pattern can be found. Nevertheless, the diffraction peaks of the sample are quite similar to JCPDS No. 27-0726 in both their positions and relative intensities, which indicates the sample is directly indexed to the pure hexagonal NaLuF4 crystal. 6
The as-prepared NaLuF4:Yb3+,Er3+,Tm3+ crystals with pure hexagonal phase exhibit morphology of nanorod, as shown in Fig. 2. The SEM image in Fig. 2A reveals that β-NaLuF4:Yb3+, Er3+, Tm3+ consists of hollow and hexagonal rod morphologies. The SEM image in Fig. 2A reveals that the NaLuF4:Yb, Er, Tm consists of uniform hexagonal microtubes 2–3 µm in length and 300-500 nm in diameter.
It can be seen that the particles present the similar morphology and size
distribution. However, the size and morphology and size of the particles are not relatively uniform and regular. Although the aggregation of the particles is still observed through the molten salt method, the temperature is much lower than that of solid state reaction and the reaction period is much shorter. Therefore, this can save a lot of energy resource. In Fig. 2B, EDS shows a characteristic intensity profile of Na, Lu and F elements. As the low doping amount of Er and Tm, it is difficult to distinguish their energy spectrum, but the characteristic peaks in the up-conversion fluorescence spectra can prove the existence of these two elements. When Nd3+ was doped in NaLuF4:Yb3+,Er3+,Tm3+, the XRD of the new sample was changed. As shown in Fig. 3, in addition to the original hexagonal phase, the cubic NaLuF4 appeared which indicated that the crystal phase was changed by doping Nd3+. This is because the ion radius of Nd3+ is 141 pm which is larger than that of Lu3+(the radius is 84.89 pm), and the difference is obvious, so the transformation of the crystal phase is produced in the synthesis process. We also investigate the XRD patterns of Nd3+ doped samples with different concentrations. When the concentration of Nd3+ increased, the shape of the peak becomes disordered, which affect the change of the 7
crystallites becomes large. And the lowest Nd3+ concentration to induce such change is 5%. The as-prepared NaLuF4:Yb3+,Nd3+,Er3+,Tm3+ crystals exhibit nano-rod morphologies, which are shown in Fig. 4A. The EDS (Fig. 4B) confirms the presence of Na, Lu, Yb, Nd and F elements, which indicates that the Nd3+ has been successfully doped in the crystals. UC luminescence properties It is well acknowledged that rare earth (RE) fluorides (especially NaREF4 or REF3) are excellent host lattices for the luminescence of various lanthanide ions. To investigate the luminescent properties of as-synthesized nanorod bundles, NaLuF4 doped with different RE ions was designed and discussed. It is acknowledged that, when sensitized by Yb3+, Er3+ can emit high intensity UC luminescence in red and green wavelength range under the excitation of infrared light. Fig. 5A gives the UC spectrum of NaLuF4:Yb3+, Er3+. It can be seen that NaLuF4:Yb3+, Er3+ sample can emit the characteristic Er3+ transition bands centered at 411 nm (from 2H9/2 to 4I15/2 ), 521 nm (from 2H11/2 to 4I15/2), 541 nm (from 4S2/3 4
to
I15/2), and 655 nm (from 4F9/2 to 4I15/2). It should point out that the observation of 411
nm emission indicates the high UC efficiency of as-prepared NaLuF4 host. Because generally, the 411 nm emission could not be observed due to the low efficiency of three or four-photon UC and strong scattering of host lattices. In Fig. 5B for NaLuF4:Yb,Tm nanorods, the three emission bands at around 475 nm, 655 nm and 700 nm can be assigned to the thermalized from 1D2 to 3F4, from 1G4 to 3H6, from 1G4 to 3F4, and from 3F3 to 3H6 transition of Tm3+, respectively. For NaLuF4:Yb3+, Er3+,
8
Tm3+ nanorods in Fig. 5C, the Er3+ ions generate a very strong red transition (from 1
G4 to 3F4) at 648 nm. Moreover, we can also find that relative emission intensities of
the red, green and blue colors. The respective CIE (commission Internationale de I’Eclairage 1931 chromaticity) coordinates for UC emission spectra of NaLuF4:Yb,Er, NaLuF4:Yb,Tm and NaLuF4:Yb,Er,Tm products are given in the Fig. 5D. Furthermore, there is a simple regularity to each phosphor, the CIE chromaticity values of different doping level samples are arranged approximately in line, which would be a date base for further study in the color parameters of this kind of phosphors. The CIE chromaticity coordinates (x, y) of NaLuF4:33%Yb3+, x%Er3+,2%Tm3+ (x = 0, 1, 1.5, 2) with different Er3+ concentration are summarized in Table 1. As illustrated, by changing of Er3+ doping concentration the chromaticity coordinates changes, and the luminescent colors can be altered in a wide scope (Fig. 6). And the luminescent colors were changed from blue to white, then to yellow. Specially, when the doping concentration of Er3+ was 1%, the output color becomes white. Moreover, the precise control of the intensity balance for blue, green and red emissions by co-doping Yb3+/ Er3+/Tm3+, the output color change from blue to yellow basic colors by simply tuning the Er3+ doping concentration may also offer a simple and efficient method to obtain a desired color. We next examined the emission intensity of NaLuF4:Yb3+, Er3+, Nd3+ with different concentrations of Nd3+ dopants from 5% to 30%. As shown in Fig. 7A, the UCL intensity of the NaLuF4:Yb3+,Er3+,Nd3+ is affected by Nd3+ ions, in detail, decreased 9
upon increasing the concentration of Nd3+ from 5% to 30 mol% in the naked-core nanoparticles. And Fig. 7B gives the original UC spectra of NaLuF4:Yb3+, Er3+, Nd3+ with different doping concentrations of Nd3+(5% - 30%). It can be observed that all five NaLuF4:Yb3+, Er3+, Nd3+ samples can send out the symbolic Er3+ transition bands focus on
411, 521, 541 and 655 nm, which indicating that Er3+ successfully doped
into the NaLuF4 nanoparticles. As shown in Fig. 7C, the peak area ratio of the red area (from 4F9/2 to 4I15/2) to the green area (from2H11/2，4S3/2 to 4I15/2) tunes from 1.75 to 2.71 with the changing of Nd3+ concentration. When the doped Nd3+ concentration is increased to 30 – 40%, the luminescent intensity reduced. This phenomenon is resulted from energy back-transfer from Er3+ to Nd3+ which produces the energy quenching. While the doped Nd3+ concentration increased the degree of quenching, which lead to the decrease of emission intensity. Table 2 shows the effect of different doped Nd3+ on the calculated CIE chromaticity coordinates of NaLuF4:33%Yb3+,1%Er3+,x%Nd3+. As shown, the chromaticity coordinates alter with the tune of Nd3+ doping concentration, and the luminescent colors can be changed in a wide scope. Fig. 5D illustrated the tunable color region for Yb3+ doped NaLuF4:Yb3+, Er3+. All kinds of luminescence colors and wide color area of the NaLuF4:Yb3+, Er3+, Tm3+ samples under 980 nm LD excitation devote themselves great potential applications in a variety of areas. More importantly, the accurate command of the intensity balance for the red, white and yellow colors by simply changing the Yb3+ doping concentration may also offering an effective and convenient method to obtain a perfect color. 10
The NaLuF4 phosphors co-doped with 33%Yb3+, 2%Tm3+ and x% Nd3+ ions (x = 5, 10, 20, and 30) were also prepared, and transitions of Tm3+ (from 1D2 to 3F4 at 450 nm, and from 1G4 to 3H6 at 480 nm ions) were found. With an increasing in the doped Nd3+ concentration, the relative intensities of the blue and red bands altered. Fig. 8B illustrates the original UC luminescence spectra excited by 980 nm LD. It can be seen that all five NaLuF4:Yb3+, Tm3+, Nd3+ samples can emit characteristic Tm3+ transition bands centered at 475, 644 and 700 nm, which indicating that Tm3+successfully doped into the NaLuF4 nanoparticles. As illustrated in Fig. 7C, the peak area ratio of the red area becomes obvious by changing of Nd3+ concentration. When the doped Nd3+ concentration is 5 - 10%, the blue emission is most powerful emission color. While the doped Nd3+ concentration is changed to 20 - 30%, the variation trend of blue emission becomes obvious. Table 3 shows the effect of different doped Nd3+ on the calculated CIE chromaticity coordinates of NaLuF4:33%Yb3+,2%Tm3+,x%Nd3+. As shown, by altering the Nd3+ doping concentration the chromaticity coordinates changes, and the luminescent colors can be changed in a wide range. Fig. 8D illustrated the tunable color region for Nd3+ doped NaLuF4:Yb3+, Tm3+, which is marked by the solid-lined. These abundant luminescence colors and wide color area of the NaLuF4:Yb3+, Tm3+, Nd3+ phosphors under 980 nm LD excitation devote themselves great potential applications in a variety of areas. More importantly, by simply adjusting the Nd3+ doping concentration may also provide a convenient and effective method to obtain a
11
perfect color, the precise command of the intensity balance for the green, red and blue colors. We finally examined the emission intensity of NaLuF4:Yb3+,Er3+,Tm3+,Nd3+ with different concentration of Nd3+ dopants from 5% to 30%. As shown in Fig. 9A, the UCL intensity of NaLuF4:Yb3+, Er3+, Tm3+, Nd3+ which is affected by the Nd3+ ions decreased upon increasing the concentration of Nd3+ from 5 to 30 mol% in the naked-core nanoparticles. From Fig.9 A we can see the blue (450 and 480 nm) green (520 and 540 nm), and red (655 nm) emissions. Compared with the UC spectra
of
NaLuF4:33%Yb3+,1%Er3+,
x%Nd3+
(Fig.7A)
and
NaLuF4:33%Yb3+,2%Tm3+,x% Nd3+(Fig.8A) (x = 5, 10, 20, 30), it is easy to assign the origins of the observed emission bands. The blue emissions centered at 450 and 480 nm are generated from the electronic transitions of Tm3+(1D2→3F4, and 1G4→3H6). The green and red emissions originate frm the electronic transion of Er3+ ions at 520 (2H11/2→4I15/2), 540 (4S3/2→4I15/2) and 655(4F9/2→4I15/2). It is noted that Tm3+ions also generate a very weak red transion of 1G4→3F4 at 648 nm.[33-35] Which may be covered by red emission of Er3+ ion. Moreover, we can also find that the relative emission intensities of red, green and blue colors change with Nd3+ concentrations. And Fig. 9B shows the original UC luminescence spectra of NaLuF4:Yb3+, Er3+,Tm3+, Nd3+ with different concentrations of Nd3+ (5% - 30%) excited by 980 nm LD. It can be seen that all five NaLuF4:Yb3+,Er3+,Tm3+,Nd3+ samples can emit characteristic Er3+ and Tm3+ transition bands which indicating that both the ions were successfully doped into the NaLuF4 12
nanoparticles. As illustrated in Fig. 9C, the peak area ratio of the green area becomes obvious with the changing of Nd3+ concentration. When the doped Nd3+ concentration is 5 –10%, the green emission is the strongest emission color. While the doped Nd3+ concentration is changed to 20 - 30%, the variation trend of green emission becomes obvious. Table 4 shows the change of different doped Nd3+ on the calculated CIE chromaticity coordinates of NaLuF4:33%Yb3+,1%Er3+,2%Tm3+,x%Nd3+. As shown, the chromaticity coordinates altered with the change of Nd3+ doping concentration, and the emitting colors can be changed in a wide range. Fig. 9D illustrates the tunable color scope for Nd3+ doped NaLuF4:Yb3+, Er3+, Tm3+. These abundant luminescence colors and wide color region of the NaLuF4:Yb3+, Er3+, Tm3+, Nd3+ phosphors under 980 nm LD excitation devotes themselves many potential applications in a variety areas. More importantly, the precise control of the intensity balance for the green, blue and red colors by simply changing the Nd3+ doping concentration may also offer a convenient and efficient way to obtain a desired color.
4. Conclusions In conclusion, NaLuF4 nanorods have been firstly prepared through a simple one-pot molten salt procedure. The phase and morphology were well discussed. The UC luminescence properties of NaLuF4 crystals doped with different RE ions (Yb3+/Er3+/Nd3+, Yb3+/Tm3+/Nd3+ , Yb3+/Er3+/Tm3+/Nd3+) were researched under 980 nm LD excitation. By adjusting the Nd3+ doping concentration, the relative emission
13
colors intensities can be precisely commanded resulting in a variety of visible emissions. More importantly, by controlling the emission intensity balance for the three green, blue, and red basic colors, white light luminescence are gained in the NaLuF4:Yb3+, Er3+,Tm3+, Nd3+ sample. The consequence indicate a general procedure for the progress of highly-efficient luminescent UC phosphors in a wide color range, which have many potential applications in a variety of areas
Acknowledgments Financial support from National Natural Science Foundation of China (NSFC 51702070, 21676066), Natural Science Foundation of Heilongjiang Province (QC2017006), Harbin Science and Technology Youth Reserve Talent Project (2017RAQXJ077), 2017T00228),
and
China
Postdoctoral
Heilongjiang
Science
Postdoctoral
Foundation
(2016M600241,
Foundation(LBH-Z16050),
Fundamental Research Funds for the Harbin Engineering University are greatly acknowledged.
References [1] L. T. Liu, L. H. Cheng, B. J. Chen, J. Y. Shang, X. H. Qi, Y. A. Zhu and R. N. Hua, Dependence of optical temperature sensing and photo-thermal conversion on particle size and excitation wavelength in β-NaYF4:Yb3+, Er3+ nanoparticles, J. Alloys Compd., 741, 2018, 927-936. [2] Q. Luo, X. S. Deng, W. H. Chen, H. Guo, O. Y. Wei, X. H. Chen and S. M. Huang, Enhancing upconversion from NaYF4:Yb,Er@NaYF4 core–shell 14
nanoparticles assembled on metallic nanostructures, J. Nanosci Nanotechno., 18, 2018, 5063-5073. [3] C. Zhu, W. Y. Zhou, J. J. Fang, Y. R. Ni, L. Fang, C. H. Lu, Z. Z. Xu and Z. T. Kang, Improved upconversion efficiency and thermal stability of NaYF4@SiO2 photonic crystal film, J. Alloys Compd., 741, 2018, 337-347. [4]
Y. Gao, J. Z. Feng, C. Shi, M. M. Fan, GuiyanZhao, Y. F. Bi, Y. G. Sun, F. Ding and Z. H. Xu,
Highly uniform hollow GdF3 ellipsoids: controllable synthesis,
characterization and
up-conversion luminescence properties, J. Nanosci
Nanotechno., 18, 2018, 5822-5827. [5] P. Du, X. Y. Huang and J. S. Yu, Facile synthesis of bifunctional Eu3+-activated NaBiF4 red-emitting nanoparticles for simultaneous white light-emitting diodes and field emission displays, Chem. Eng. J., 337, 2018, 91-100. [6] X. Q. Zhao, H. Suo, Z. Y. Zhang and C. F. Guo, Cross-relaxation and non-steady-state processes induced up-conversion color modulation in Gd2O3: Ln3+/Er3+ (Ln = Tm, Ho), Dyes Pigments, 151, 2018, 335-341. [7] D. den Engelsen, G. R. Fern, T. G. Ireland and J. Silver, Reassignment of electronic transitions in the laser-activated spectrum of nanocrystalline Y2O3:Er3+, J. Lumin., 196, 2018, 337-346. [8] Z. A. S. Mahraz, M. R. Sahar and S. K. Ghoshal, Near-infrared up-conversion emission from erbium ions doped amorphous tellurite media: Judd-Ofelt evaluation, J. Alloys Compd., , 740, 2018, 617-625. [9] Z. H. Zhao, X. Zhang, J. M. Fan, D. F. Xue, B. Zhang and S. Yin, 15
N-TiO2/g-C3N4/Up-conversion phosphor composites for the full-spectrum light-responsive deNO x photocatalysis, J. Mater. Sci., 53, 2018,7266-7278. [10] R. Lv, D. Yang, P. Yang, J. Xu, F. He, S. Gai, C. Li, Y. Dai, G. Yang and J. Lin, Integration of upconversion nanoparticles and ultrathin black phosphorus for efficient photodynamic theranostics under 808 nm near-infrared light irradiation, Chem. Mater., 28 (13), 2016, 4724-4734. [11] H. Bi, Y. Dai, R. Lv, C. Zhong, F. He, S. Gai, A. Gulzar, G. Yang and P. Yang, Doxorubicin-conjugated CuS nanoparticles for efficient synergistic therapy triggered by near-infrared light, Dalton. T., 45, 2016, 5101-5110. [12] L. Feng, F. He, B. Liu, G. Yang, S. Gai, P. Yang, C. Li, Y. Dai, R. Lv and J. Lin, g-C3N4 coated upconversion nanoparticles for 808 nm near-infrared light triggered
phototherapy
and
multiple
imaging,
Chem.
Mater.,28,
2016,7935-7946. [13] J. F. Tang, Y. W. Huang, M. J. Sun, J. Gou, Y. Zhang, G. N. Li, Y. C. Kang, J. Yang and Z. H. Xiao, Spectroscopic characterization and temperature-dependent upconversion behavior of Er3+ and Yb3+ co-doped zinc phosphate glass, J. Lumin., 197, 2018,, 153-158. [14] N. Niu, P. P. Yang, F. He, X. Zhang, S. L. Gai, C. X. Li and J. Lin, Tunable multicolor and bright white emission of one-dimensional NaLuF4:Yb3+,Ln3+ (Ln = Er, Tm, Ho, Er/Tm, Tm/Ho) microstructures, J. Mater. Chem., 22, 2012, 10889-10899. [15] A. Bagheri, H. Arandiyan, C. Boyer, M. Lim, Lanthanide-doped upconversion 16
nanoparticles: emerging intelligent light-activated drug delivery systems, Adv. Sci. 3 , 2016. [16]T. S. Yang, Y. M. Wang, H. Gao, Q. Liu and K. Y. Zhang, Eur. RGD-Peptide-Modified
NaLuF4:Yb,Er
nanocrystals
for
upconversion-luminescence-targeted tumor-cell imaging, J. Inorg. Chem., 44, 2017, 5169-5175. [17] M. Y. Ding, D. Q. Chen, C. H. Lu, J. H. Xi, Z. G. Ji and Z. Z. Xu, Hydrothermal synthesis,
energy
transfer
and
luminescent
properties
of
β-NaLuF4:Ce3+/Gd3+/Sm3+ microcrystals, J. Lumin., 186, 2017, 109-116. [18] L. L. Tong, X. P. Li, R. N. Hua, L. H. Cheng, J. S. Sun, J. S. Zhang, S. Xu, H. Zheng, Y. Q. Zhang and B. J. Chen, Optical temperature sensing properties of Yb3+/Tm3+ co-doped NaLuF4 crystals , Curr. Appl. Phys. , 17, 2017, 999-1004. [19] A. Xie and C. Y. Cao, Synthesis and Optical Properties of Yb3 +/Er3 +, Yb3 +/Tm3 +, Eu3 + Doped NaLuF4, Na5Lu9F32, KLu3F10, and KLu2F7, Nanosci. Nanotech. Let., 9, 2017,305-309. [20] H. Y. Lu, H. Y. Hao, H. M. Zhu, G. Shi, Q. D. Fan, Y. L. Song, Y. X. Wang and X. R. Zhang, Enhancing temperature sensing behavior of NaLuF4:Yb3+/Er3+via incorporation of Mn2+ ions resulting in a closed energy transfer, J. Alloys Compd., 728, 2017, 971-975. [21] Y. Liu, N. Kang, J. Lv, Z. Zhou, Q. Zhao, L. Ma, Z. Chen, L. Ren, L. Nie, Deep photoacoustic/luminescence/magnetic resonance multimodal imaging in living subjects using high-efficiency upconversion nanocomposites, Adv. Mater. 17
28 ,2016, 6411–6419. [22] D. P. Yang, C. Cao, W. Feng, C. H. Huang and F. Y. Li, Synthesis of NaYF4:Nd@NaLuF4@SiO2@PS Colloids for Fluorescence Imaging in the Second Biological Window, J. Rare Earth., 36, 2018, 113-118. [23] X. B. Li, S. L. Gai, C. X. Li, D. Wang, N. Niu, F. He and P. P. Yang, Monodisperse lanthanide fluoride nanocrystals: synthesis and luminescent properties, Inorg. Chem., 51, 2012, 3963-3971. [24] S. L. Gai, G. X. Yang, X. B. Li, C. X. Li, Y. L. Dai, F. He and P. P. Yang, Facile synthesis and up-conversion properties of monodisperse rare earth fluoride nanocrystals, Dalton. T., 41, 2012,
11716-11724.
[25] S. L. Gai, P. P. Yang, X. B. Li, C. X. Li, D. Wang, Y. L. Dai and J. Lin, Monodisperse CeF3, CeF3:Tb3+, and CeF3:Tb3+@LaF3 core/shell nanocrystals: synthesis and luminescent properties, J. Mater. Chem., 21, 2011, 14610-14615. [26] C. N. Zhong, P. A. P. Yang, X. B. Li, C. X. Li, D. Wang, S. L. Gai and J. Lin, Monodisperse bifunctional Fe3O4@NaGdF4:Yb/Er@NaGdF4:Yb/Er core–shell nanoparticles, Rsc Adv., 2, 2012, 3194-3197. [27] K. K. Patankar, D. M. Ghone, V. L. Mathe and S. D. Kaushik, Structural and physical property study of sol–gel synthesized CoFe2−xHoxO4 Nano Ferrites, J. Magn. Magn. Mater., 454, 2018, 71-77. [28] J. Fu, Y. D. Hou, M. P. Zheng and M. K. Zhu, Comparative study of dielectric properties of the PVDF composites filled with spherical and rod-like BaTiO3 derived by molten salt synthesis method, J. Mater. Sci., 53, 2018, 7233-7248. 18
[29] L. Tian, J. Y. Li, F. Liang, J. K. Wang, S. S. Li, H. J. Zhang and S. W. Zhang, Molten salt synthesis of tetragonal carbon nitride hollow tubes and their application for removal of pollutants from wastewater,
Appl. Catalysis
B-Environmental, 225, 2018, 307-313. [30] L. Mukhopadhyay, V. K. Rai, R. Bokolia, K. Sreenivas, 980 nm excited Er3+/Yb3+ /Li3+ /Ba2+ : NaZnPO4 upconverting phosphors in optical thermometry , J. Lumin., 187, 2017, 368-377. [31] L. Mukhopadhyay, V. K. Rai, Upconversion based near white light emission, intrinsic
optical
bistability
and
temperature
sensing
in
Er3+/Tm3+
/Yb3+/Li+ :NaZnPO 4 phosphors, New J. Chem. 41, 2017, 7650-7661. [32] Y. Tian, Y. H. Fang, B. N. Tian, C. Cui, P. Huang, L. Wang, H. Y Jia, B. J. Chen, Molten salt synthesis, energy transfer, and temperature quenching fluorescence of green-emitting β-Ca2P2O7:Tb
3+
phosphors, J. Mater. Sci., 50, 2015,
6060-6065. [33] M. C. Wong, C. Li, M. K. Tsang, Y. Zhang, J. H. Hao, Magnetic-Induced Luminescence from Flexible Composite Laminates by Coupling Magnetic Field to Piezophotonic Effect, Adv. Mater., 27, 2015, 4488-4495. [34] G. X. Bai, S. G. Yuan, Y. D. Zhao, Z. B. Yang, S. Y. Choi, Y. Chai, S. F. Yu, S. P. Lau, J. H. Hao, 2D Layered Materials of Rare-Earth Er-Doped MoS 2 with NIR-to-NIR Down- and Up-Conversion Photoluminescence, Adv. Mater., 28, 2016, 7472-7477. [35] M. C. Wong, C. Li, G. G. Bai, L. B. Huang, J. H. Hao, Temporal and Remote 19
Tuning of Piezophotonic-Effect-Induced Luminescence and Color Gamut via Modulating Magnetic Field, Adv. Mater., 29, 2017, 170945.
Fig. 1 XRD patterns of NaLuF4:Yb, Er, Tm prepared at 350℃ for reaction time of 3 h, and the standard data of hexagonal β-NaLuF4 (JCPDS No. 27-0726).
Fig. 2 (A) Low magnification SEM images and (B) EDS of NaLuF4:Yb,Er,Tm.
20
Fig.3 XRD patterns of NaLuF4:Yb3+,Nd3+,Er3+,Tm3+ prepared at 350℃ and the standard data of cubic α-NaLuF4 (JCPDS No. 27-0725) and hexagonal β-NaLuF4 (JCPDS No. 27-0276).
Fig. 4 (A) Low magnification SEM images and (B) EDS of NaLuF4:Yb,Er,Tm,Nd
21
Fig.5
(A)
The
UC
luminescence
properties
of
NaLuF4:Yb3+,Er3+,
NaLuF4:Yb3+,Tm3+, and (C) the CIE chromaticity of the three crystals.
22
(B)
Fig.6 the CIE chromaticity of NaLuF4:33%Yb3+, x%Er3+, 2%Tm3+.
Fig.7 (A) Comparable and (B) original UC luminescence properties of NaLuF4:33%Yb3+,1%Er3+,x%Nd3+ with different Nd3+ concentrations. (C) Peak area ratio
of
red
and
green
emissions.
(D)
The
CIE
chromaticity
NaLuF4:33%Yb3+,1%Er3+,x%Nd3+ showing the tunable color region. 23
of
Fig.8 (A) Comparable and (B) original UC luminescence properties of NaLuF4:33%Yb3+,2%Tm3+, x%Nd3+. (C) Peak area ratio of red, green and blue emissions. (D) The CIE chromaticity of NaLuF4:33%Yb3+, 2%Tm3+,x%Nd3+ showing the tunable color region of Yb3+/Tm3+/Nd3+ doped crystals.
24
Fig. 9 (A) Comparable and (B) original UC luminescence properties of NaLuF4:33%Yb3+,2%Er3+,1%Tm3+,x%Nd3+ with different Nd3+ doping concentration. (C) Peak area ratio of blue, green and red emissions. (D) The CIE chromaticity of NaLuF4:Yb3+,Er3+,Tm3+,x%Nd3+ doped crystals.
Table
1
The
calculated
CIE
chromaticity
coordinates
NaLuF4:33%Yb3+,x%Er3+,2%Tm3+ samples. samples NaLuF4:33%Yb3+,0%Er3+,2%Tm3+
x 0.2271
y 0.1162
NaLuF4:33%Yb3+,1%Er3+,2%Tm3+
0.3050
0.2670
NaLuF4:33%Yb3+,1.5%Er3+,2%Tm3+ 0.3352
0.4297
NaLuF4:33%Yb3+,2%Er3+,2%Tm3+ 25
0.3549
0.4757
(x,
y)
of
Table
2
The
calculated
CIE
chromaticity
coordinates
(x,
y)
of
(x,
y)
of
(x,
y)
of
NaLuF4:33%Yb3+,1%Er3+,x%Nd3+ samples.
Table
3
samples NaLuF4:33%Yb3+,1%Er3+,5%Nd3+
x 0.3584
y 0.6007
NaLuF4:33%Yb3+,1%Er3+,10%Nd3+
0.3628
0.5919
NaLuF4:33%Yb3+,1%Er3+,20%Nd3+
0.3721
0.5754
NaLuF4:33%Yb3+,1%Er3+,30%Nd3+
0.3989
0.5190
The
calculated
CIE
Chromaticity
coordinates
NaLuF4:33%Yb3+,2%Tm3+
Table
4
samples NaLuF4:33%Yb3+,2%Tm3+,5%Nd3+
x 0.1529
y 0.0753
NaLuF4:33%Yb3+,2%Tm3+,10%Nd3+
0.1584
0.0915
NaLuF4:33%Yb3+,2%Tm3+,20%Nd3+
0.1962
0.1539
NaLuF4:33%Yb3+,2%Tm3+,30%Nd3+
0.2638
0.2604
The
calculated
CIE
chromaticity
coordinates
NaLuF4:33%Yb3+,1%Er3+,2%Tm3+,x%Nd3+ samples NaLuF4:33%Yb ,1%Er3+,2%Tm3+,5%Nd3+
x 0.2455
y 0.4958
NaLuF4:33%Yb3+,1%Er3+,2%Tm3+,10%Nd3+
0.2660
0.5625
NaLuF4:33%Yb3+,1%Er3+,2%Tm3+,20%Nd3+
0.2844
0.5243
NaLuF4:33%Yb3+,1%Er,2%Tm3+,30%Nd3+
0.2891
0.4363
3+
26
1.
In this study, we firstly proposed a strategy to preparing one-dimensional NaLuF4:Yb3+,Nd3+, Er3+, Tm3+ nanorods by a surfactant-free molten salt method .
2.
Upon 980 nm laser diode (LD) excitation, white up-conversion light was successfully achieved by properly tuning the sensitizer (Nd3+) concentration in the host matrix.