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Electronic Supplementary Material “Chameleon-like” optical behavior of lanthanide-doped fluoride nanoplates for multilevel anti-counterfeiting applications Wenwu You, Datao Tu ( ), Renfu Li, Wei Zheng, and Xueyuan Chen ( ) CAS Key Laboratory of Design and Assembly of Functional Nanostructures, and Fujian Key Laboratory of Nanomaterials, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China Supporting information to https://doi.org/10.1007/s12274-019-2366-z Experimental Chemicals and materials NaHF2, cyclohexane, and ethanol were purchased from Sinopharm Chemical Reagent Co., China. Oleic acid (OA) and 1-octadecene (ODE) and rare earth acetates were purchased from Sigma-Aldrich (China). All chemicals were used as received without further purification. Synthesis of NaYbF4:2%Er core nanoplates (NPs) 0.8 mmol of Yb(CH3COO)3, 0.18 mmol of Yb(CH3COO)3, and 0.02 mmol of Er(CH3COO)3 were mixed with 8 mL of OA and 12 mL of ODE in a 100 mL two-neck round-bottom flask. The resulting mixture was heated to 180 °C under N2 flow with vigorous stirring for 10 min to form a clear solution and then cooled down to room temperature (RT). Thereafter, 2 mmol of NaHF2 powder was added into the mixture solution, and the resulting solution was heated to 310 °C under N2 flow with vigorous stirring and maintained for 60 min, and then cooled down to RT. The obtained NaYbF4:2%Er core NPs were precipitated by addition of 20 mL of ethanol, collected by centrifugation at 10000 rpm for 3 min, washed with ethanol and cyclohexane several times, and dried at 80 °C in an oven for 8 h. Synthesis of NaYbF4:2%Er@NaYF4 core/shell NPs Briefly, 0.5 mmol of Y(CH3COO)3 was mixed with 8 mL of OA and 12 mL of ODE in a 100 mL two-neck round-bottom flask. Thereafter, 0.5 mmol of NaYbF4: 2%Er core NPs in 5 mL of cyclohexane was added to the above solution and maintained at 80 °C under N2 flow with constant stirring for 10 min to remove cyclohexane. The resulting mixture was heated to 180 °C and maintained at this temperature for 20 min. Then the solution was cooled down to RT, followed by adding 1 mmol of NaHF2 powder to the solution. After that, the resulting solution was heated to 310 °C under N2 flow with vigorous stirring for 35 min. Finally, the solution was cooled down to RT and the core/shell NPs were precipitated by addition of 20 mL of ethanol. The obtained core/shell NPs were collected by centrifugation, washed with ethanol and cyclohexane several times, and then dried at 80 °C in an oven for 8 h. Synthesis of LiYbF4:2%Er@LiYF4 nanocrystals (NCs) The LiYbF4:2%Er@LiYF4 NCs were prepared by a previously reported method [S1]. For synthesis of LiYbF4:2%Er core NCs, 1 mmol of CH3COOLi, 0.98 mmol of Yb(CH3COO)3 and 0.02 mmol of Er(CH3COO)3 were mixed with 8 mL of OA and 12 mL of trioctylamine (TOA) in a 100 mL two-necked round-bottom flask. The resulting mixture was heated to 160 °C under a N2 flow with constant stirring for 30 min to form a clear solution, and then cooled down to RT. Thereafter, 10 mL of methanol solution containing 4 mmol of NH4F was added and the solution, which was stirred at 60 °C for 30 min to remove methanol. After methanol was evaporated, the resulting solution was heated to 320 °C under a N2 flow with vigorous stirring for 60 min, and then cooled down to RT. The obtained LiYbF4:2%Er core NCs were precipitated by addition of 30 mL of ethanol, collected by centrifugation, washed with ethanol several times, and finally redispersed in cyclohexane. For synthesis of LiYbF4:2%Er@LiYF4 NCs, 0.5 mmol of CH3COOLi and 0.5 mmol of Y(CH3COO)3·were added to a 100 mL two-necked round-bottom flask containing 8 mL of OA and 12 mL of TOA. The mixed solution was then heated to 160 °C under a N2 flow with constant stirring for 30 min to form a clear solution. After cooling down to 80 °C, 0.5 mmol of LiYbF4:2%Er core NCs in 10 mL of cyclohexane was added and maintained at 80 °C for 30 min to remove cyclohexane. After that, 10 mL of methanol solution containing 2 mmol of NH4F was added and stirred at 60 °C for another 30 min to remove methanol. Subsequently, the solution was heated to 320 °C under a N2 flow with vigorous stirring for 60 min, and then cooled down to RT. The resulting LiYbF4:2%Er@LiYF4 NCs were precipitated by addition of 30 mL of ethanol, collected by centrifugation, washed with ethanol several times, and finally dried at 80 °C for 8 h. Structural and optical characterization Powder X-ray diffraction (XRD) patterns of the as-prepared NPs were collected with an X-ray diffractometer (MiniFlex 600, Rigaku) with Cu Kα1 radiation (λ = 0.154187 nm). Transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission Address correspondence to Datao Tu, [email protected]; Xueyuan Chen, [email protected]

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Page 1: “Chameleon-like” optical behavior of lanthanide-doped fluoride ......“Chameleon-like” optical behavior of lanthanide-doped fluoride nanoplates for multilevel anti-counterfeiting

Electronic Supplementary Material

“Chameleon-like” optical behavior of lanthanide-doped fluoride nanoplates for multilevel anti-counterfeiting applications Wenwu You, Datao Tu (), Renfu Li, Wei Zheng, and Xueyuan Chen ()

CAS Key Laboratory of Design and Assembly of Functional Nanostructures, and Fujian Key Laboratory of Nanomaterials, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China Supporting information to https://doi.org/10.1007/s12274-019-2366-z

Experimental

Chemicals and materials

NaHF2, cyclohexane, and ethanol were purchased from Sinopharm Chemical Reagent Co., China. Oleic acid (OA) and 1-octadecene (ODE) and rare earth acetates were purchased from Sigma-Aldrich (China). All chemicals were used as received without further purification.

Synthesis of NaYbF4:2%Er core nanoplates (NPs)

0.8 mmol of Yb(CH3COO)3, 0.18 mmol of Yb(CH3COO)3, and 0.02 mmol of Er(CH3COO)3 were mixed with 8 mL of OA and 12 mL of ODE in a 100 mL two-neck round-bottom flask. The resulting mixture was heated to 180 °C under N2 flow with vigorous stirring for 10 min to form a clear solution and then cooled down to room temperature (RT). Thereafter, 2 mmol of NaHF2 powder was added into the mixture solution, and the resulting solution was heated to 310 °C under N2 flow with vigorous stirring and maintained for 60 min, and then cooled down to RT. The obtained NaYbF4:2%Er core NPs were precipitated by addition of 20 mL of ethanol, collected by centrifugation at 10000 rpm for 3 min, washed with ethanol and cyclohexane several times, and dried at 80 °C in an oven for 8 h.

Synthesis of NaYbF4:2%Er@NaYF4 core/shell NPs

Briefly, 0.5 mmol of Y(CH3COO)3 was mixed with 8 mL of OA and 12 mL of ODE in a 100 mL two-neck round-bottom flask. Thereafter, 0.5 mmol of NaYbF4: 2%Er core NPs in 5 mL of cyclohexane was added to the above solution and maintained at 80 °C under N2 flow with constant stirring for 10 min to remove cyclohexane. The resulting mixture was heated to 180 °C and maintained at this temperature for 20 min. Then the solution was cooled down to RT, followed by adding 1 mmol of NaHF2 powder to the solution. After that, the resulting solution was heated to 310 °C under N2 flow with vigorous stirring for 35 min. Finally, the solution was cooled down to RT and the core/shell NPs were precipitated by addition of 20 mL of ethanol. The obtained core/shell NPs were collected by centrifugation, washed with ethanol and cyclohexane several times, and then dried at 80 °C in an oven for 8 h.

Synthesis of LiYbF4:2%Er@LiYF4 nanocrystals (NCs)

The LiYbF4:2%Er@LiYF4 NCs were prepared by a previously reported method [S1]. For synthesis of LiYbF4:2%Er core NCs, 1 mmol of CH3COOLi, 0.98 mmol of Yb(CH3COO)3 and 0.02 mmol of Er(CH3COO)3 were mixed with 8 mL of OA and 12 mL of trioctylamine (TOA) in a 100 mL two-necked round-bottom flask. The resulting mixture was heated to 160 °C under a N2 flow with constant stirring for 30 min to form a clear solution, and then cooled down to RT. Thereafter, 10 mL of methanol solution containing 4 mmol of NH4F was added and the solution, which was stirred at 60 °C for 30 min to remove methanol. After methanol was evaporated, the resulting solution was heated to 320 °C under a N2 flow with vigorous stirring for 60 min, and then cooled down to RT. The obtained LiYbF4:2%Er core NCs were precipitated by addition of 30 mL of ethanol, collected by centrifugation, washed with ethanol several times, and finally redispersed in cyclohexane. For synthesis of LiYbF4:2%Er@LiYF4 NCs, 0.5 mmol of CH3COOLi and 0.5 mmol of Y(CH3COO)3·were added to a 100 mL two-necked round-bottom flask containing 8 mL of OA and 12 mL of TOA. The mixed solution was then heated to 160 °C under a N2 flow with constant stirring for 30 min to form a clear solution. After cooling down to 80 °C, 0.5 mmol of LiYbF4:2%Er core NCs in 10 mL of cyclohexane was added and maintained at 80 °C for 30 min to remove cyclohexane. After that, 10 mL of methanol solution containing 2 mmol of NH4F was added and stirred at 60 °C for another 30 min to remove methanol. Subsequently, the solution was heated to 320 °C under a N2 flow with vigorous stirring for 60 min, and then cooled down to RT. The resulting LiYbF4:2%Er@LiYF4 NCs were precipitated by addition of 30 mL of ethanol, collected by centrifugation, washed with ethanol several times, and finally dried at 80 °C for 8 h.

Structural and optical characterization

Powder X-ray diffraction (XRD) patterns of the as-prepared NPs were collected with an X-ray diffractometer (MiniFlex 600, Rigaku) with Cu Kα1 radiation (λ = 0.154187 nm). Transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission

Address correspondence to Datao Tu, [email protected]; Xueyuan Chen, [email protected]

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Nano Res.

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electron microscopy (HAADF–STEM) image measurements were performed by using a TECNAI G2 F20 TEM equipped with the energy dispersive X-ray spectrum. The scanning electron microscope (SEM) was performed using a JSM 6700F scanning electron microscope (SEM). Downshifting luminescence (DSL) spectra were recorded on a spectrometer (FLS980, Edinburgh). Upconversion luminescence (UCL) spectra were carried out upon excitation at 980 nm with a continuous-wave semiconductor NIR laser diode (MDL-Ⅲ-980-2W, Changchun New Industries Optoelectronics Tech Co., Ltd.). UCL lifetimes were measured with a customized ultraviolet (UV) to mid-infrared steady-state and phosphorescence lifetime spectrometer (FSP920-C, Edinburgh) equipped with a digital oscilloscope (TDS3052B, Tektronix) and a tunable mid-band Optical Parametric Oscillator (OPO) pulse laser as the excitation source (410-2400 nm, 10 Hz, pulse width 5 ns, Vibrant 355II, OPOTEK). The absolute UCQYs were measured on a customized absolute UCQY measurement system combined with a fiber optic spectrometer (QE65pro, Ocean Optics).

Figure S1 Powder XRD pattern of the as-prepared NaYbF4:2%Er core and NaYbF4:2%Er@NaYF4 core/shell NPs. All of the XRD patterns can be well indexed to pure hexagonal NaYbF4 and NaYF4 (JCPDS no. 27-1427 (black line) and no. 16-0334 (red line)), indicating that the as-prepared samples have good crystallinities without any impurity phase.

Figure S2 The red-to-green (R/G) ratio for NaYbxY(0.98-x)F4:2%Er (X=0, 0.2, 0.5, 0.98) NPs upon excitation at 377 or 490 nm, respectively.

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Nano Res.

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Figure S3 (a) The upconversion luminescence (UCL) spectra of the NaYbF4:2%Er core and NaYbF4:2%Er@NaYF4 core/shell NPs upon the 980-nm laser excitation. After coating with an inert NaYF4 shell layer, the UC emission intensity of the NaYbF4:2%Er@NaYF4 core/shell NPs enhanced by ~4 times comparing with that of NaYbF4:2%Er NPs under otherwise indetical conditions. The UCL decays from (b) 2H9/2, (c) 4S3/2, and (d) 4F9/2 states of Er3+ in NaYbF4:2%Er core and NaYbF4:2%Er@NaYF4 core/shell NPs by monitoring the emission at 408, 540, and 654 nm, respectively. The measured UCL lifetime of 2H9/2, 4S3/2, and 4F9/2 states of Er3+ increase from 0.11, 0.08, and 0.52 ms in core-only NPs to 0.33, 0.34, and 0.65 ms in core/shell counterparts, respectively.

Figure S4 (a) The R/G ratio for the NaYF4 NPs doped with X%Yb,2%Er (X=98, 50, 20) upon 980-nm laser excitation with power density of 0.1, 0.5, 4.0 W/cm2, respectively. It indicates that higher concentration of Yb3+ ions results in more sensitive dependence of UCL color of Er3+ on the excitation power density.

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Nano Res.

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Figure S5 (a) Powder XRD pattern and (b) TEM image of the LiYbF4:2%Er@LiYF4 core/shell NCs. (c) The UCL spectra and (d) the corresponding CIE chromaticity coordinates of the LiYbF4:2%Er@LiYF4 NCs upon 980 nm excitation with power density of 0.1, 0.5, 4.0 W/cm2, respectively. DSL spectra of the LiYbF4:2%Er@LiYF4 NCs upon excitation at (e) 377 nm and (f) 490 nm. The UCL color of Er3+ in LiYbF4:2%Er@LiYF4 NCs is insensitive to excitation power density and ordinary multi-band emissions were obtained upon excitation at either 377 or 490 nm.

References [S1] Zou, Q.; Huang, P.; Zheng, W.; You, W.; Li, R.; Tu, D.; Xu, J.; Chen, X. Cooperative and non-cooperative sensitization upconversion in lanthanide-doped

LiYbF4 nanoparticles. Nanoscale 2017, 9, 6521-6528.