Brightly-Luminescent and Color-Tunable Camoo4:RE3+ (RE = Eu, Sm, Dy, Tb) Nanofibers Synthesized

Brightly-Luminescent and Color-Tunable CaMoO4:RE3+ (RE = Eu, Sm, Dy, Tb) nanofibers synthesized through a facile route for efficiency light-emitting-diodes

Yang Ding, Jie Liu,* Yan Zhu, Siyang Nie, Weili Wang, Junli Shi, Yanru Miu and Xibin Yu*

The Education Ministry Key Laboratory of Resource Chemistry and International Joint Laboratory of Resource Chemistry, Department of Chemistry, Shanghai Normal University, Shanghai 200234, People's Republic of China

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Experimentalsection
(1) Materials
Dimethylformamide (DMF, 99%), oleic acid (OA, 90%), oleylamine (OAM, 95%), methanol (99.9%), cyclohexane (99.5%) and toluene (99.5%) were purchased from Aladdin Reagent (China) Co. Ltd. Na2Mo04 (99%), Ca(CH3COO)2.2H2O (99.5%), HNO3 (99%), Eu2O3 (99%), Sm2O3 (99%), Dy2O3 (99%) and Tb2O3 (99%) were purchased from Shanghai Rich Joint Chemical Reagents Co. Ltd. All chemicals were used directly without any further purification.

(2) Synthesis
Preparation of a variety of rare earth nitrates.
In a typical process, Eu2O3 (1.5 g) was dissolved in the mixture of deionized water (10 mL), HNO3 (20 mL) under magnetic stirring at room temperature to form a transparent solution, then the obtained transparent solution was placed in a vacuum drying oven at 100 C for 5h. Finally, the dry Eu(NO3)3 sample could be synthesized. Others rare earth nitrates could be obtained use the similar method.
Preparation of CaMoO4:RE3+ (RE = Eu, Sm, Dy, Tb, Eu/Tb) nanofibers
In a typical synthesis of CaMoO4:0.05Eu3+ nanofibers, Na2MoO4 (1 mmol), Eu(NO3)3(0.05 mmol), Ca(CH3COO)2.2H2O (0.95 mmol), DMF (15 ml) or DMSO (15 ml), OA (0.8 mL) and OAm (0.5 mL) were loaded into a 50 mL beaker. Stronger stirring at 80 C for 30min to stabilize the transparent solution. Then, the reaction mixture was cooled by the icewater bath and excess methanol was added. the precipitates were collected by centrifugation, and washed three times with alcohol. Finally, the products were dried in a vacuum drying oven for 30 min at 60 C , the CaMoO4:0.05Eu3+ powder was dispersed in toluene or cyclohexane for further use. Others rare earth ions doped or co-doped CaMoO4 could be obtained use the similar method.

(3)Fabricating of the nanofibers based LED

0.1g Green CaMoO4:Tb3+nanofibers were directly dispersed in 5mL cyclohexane and formed atransparent and homogeneous solution.Moderate nanofibers solution wasadded into the mixture of epoxy resin (EP400A) and anhydridecuring agent (EP400B) with vigorous stirring, and the volumeratio of EP400A to EP400B was kept at 2 :1. Then, the nanofibers/epoxy resin composite put into avacuum chamber, and the mixture was heated at 60 Cfor 40 min.Finally, the green LED device was obtained, the red LED and the white LED were fabricated by using the same method.

(4) Characterization

The phase purity of the as-synthesized samples was characterized by a Rigaku DMAX-2000 (Rigaku Corporation, Tokyo, Japan) diffractometer equipped with Cu Ka radiation (k = 0.15405 A, 40 kV, 30 mA). with a scanning rate of 4 degree/min. Fourier transform infrared (FT-IR) spectrometry was carried out on a Nicolet 6700 FT-IR spectrometer, over a range from 400 cm-1 to 4000 cm-1. The UV-vis photoluminescence excitation (PLE) and emission (PL) spectra were determined on a F4600 fluorescence spectrophotometer (Hitachi High-Technologies, Tokyo, Japan) assembled with a 150 W xenon lamp as the excitation source. A JEOL JEM-200CX microscope operating at 160 kV in the bright-field mode was used for Transmission Electron Microscopy (TEM). Selected area electron diffraction (SAED) patterns were obtained on a JEOL JEM-2010 electron microscope operating at 200 kV. The luminescence decay curves were obtained using a FLSP9200 fluorescence spectra-photometer (Edinburgh Instruments Ltd., U.K.). A JEOL JSM-7500F microscope operated at an acceleration voltage of 15 kV equipped with energy dispersive X-ray analysis (EDX) facilities for elemental studies, A PR-670 spectrum scanner(Photo Research Companies, USA, scan wavelength region380–780 nm) was used for analysis of the fabricated LEDs spectra

Figure. S1TEM patterns of CaMoO4:5mol%Sm3+, CaMoO4:5mol%Dy3+and CaMoO4:5mol%Tb3+, respectively

Figure.S2EDX spectra of as-prepared nanofibers (a)CaMoO4:5mol%Eu3+ (b)CaMoO4:5mol%Sm3+(c)CaMoO4:5mol%Dy3+(d)CaMoO4:5mol%Tb3+, respectively.

Figure. S3 TEM images of the (a)CaMoO4:5mol%Dy3+,5mol%Eu3+ (b) CaMoO4:5mol%Tb3+,5mol%Eu3+(c)CaMoO4:5mol%Tb3+,5mol%Sm3+(d) CaMoO4:5mol%Tb3+,5mol%Dy3+ samples.

Figure.S4 Spectra overlap between the photoluminescence emission (PL) spectrum of CaMoO4:Tb3+ (green line) and the photoluminescence excitation (PLE) spectrum ofCaMoO4:Tb3+ (red line).

Figure. S5 Scheme of energy transfer from Tb3+ to Eu3+