Lanthanide-Doped Energy Cascade Nanoparticles: Full Spectrum Emission by Single Wavelength Excitation

Transcription

1 Supporting Information Lanthanide-Doped Energy Cascade Nanoparticles: Full Spectrum Emission by Single Wavelength Excitation Dengfeng Peng, Qiang Ju, Xian Chen, Ronghua Ma, Bing Chen, Gongxun Bai, Jianhua Hao, Xvsheng Qiao, Xianping Fan, and Feng Wang*,,# Department of Physics and Materials Science, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong SAR, China State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou , China Department of Applied Physics, The Hong Kong Polytechnic University, Hong Hum, Hong Kong SAR, China # City Universities of Hong Kong Shenzhen Research Institute, Shenzhen , China *Corresponding author. E mail: fwang24@cityu.edu.hk No financial conflict of interest was reported by the authors of this paper 1

2 Table S1. Synthe c condi ons for core shell nanopar cles of different structures and compositions. Nanoparticle a Core 1 st Shell 2 nd Shell 3 rd Shell 4 th Shell NaGdF 4 4 :Ce(15%) NaYF 4 4 :Ce(15%) F:RE=3.5 F:RE=3.5 NaGdF 4 4 :Ce(15%) NaYF 4 4 :Ce(15%) F:RE=3.5 F:RE=3.5 NaGdF NaGdF NaGdF 4 4 :Ce(15%) NaGdF 4 4 :Ce/Tb(15/1%) NaYF 4 4 :Ce/Tb(15/1%) F:RE=3.5 F:RE=3.5 NaYF 4 4 :Ce/Tb(15/1%) F:RE=4 F:RE=4 NaGdF 4 4 :Ce/Tb(15/1%) NaGdF 4 4 :Ce(15%) NaGdF 4 :Yb/Er(50/10%) NaGdF 4 4 :Ce(15%) NaGdF NaGdF OA, oleic acid; ODE, 1 octadecene; F, fluoride; RE, rare earth ions. a The percentages refer to the molar proportions of the dopant ions among all rare earth elements in the corresponding layers. 2

3 Figure S1. Control experiments demonstrating quenched emissions for most activator ions in homogeneously doped nanoparticles. The luminescence quenching can be ascribed to a redox reaction between the sensitzer and activator (for NaGdF 4 :Ce/Eu@NaGdF 4 4), to actiator cross relaxtion (for NaGdF 4 :Ce/Dy@NaGdF 4 ), and to a combined effect of redox reaction and cross relaxation (for NaGdF 4 :Ce/Sm@NaGdF 4 ). Insetss are the corresponding luminescence photos taken under indentical conditions. 3

4 Figure S2. Comparisons of optical emissions in the as synthesized Sm 3+ ions, respectivley. Insets are the corresponding luminescence photos taken under indentical conditions. A significant enhancement in optical emission nanoparticles and the ligand free counterparts activated with Tb 3+, Dy 3+, and of the nanoparticles is generally observed when oleatee ligands are removed from the nanoparticle surface. 4

5 Figure S3. Verification of the proposed screen effect. (a) Room temperature emission spetra of ligandfree NaGdF 4 :Eu(15%)@NaGdF 4 :Ce(15%) nanoparticles before and after coating with an inert NaYF 4 layer. Insets are the TEM images (scale bar: 100 nm) and the corresponding luminescence photos taken under indentical conditions. The optical emissions of the core shell nanopar cles are essentially unaffected by the inert NaYF 4 layer, suggestingg high resistance of the nanoparticles to surface quenching due to the native NaGdF 4 :Ce(15%) layer. The phonominon can be ascribed to the large energy gaps presenting in the Ce 3+ and Gd 3+ ions that are resistant to high energy oscillators. (b) Room temperaturee emission spetrum of NaGdF 4 : Eu(15%)@NaGdF 4 :Ce(15%) nanoparticles after oleate ligands were added back by heating the nanoparticles in an OA/ODE solution. The recovered broad emission along with a decrease in overall emission intensity unambiguously demonstrates the screen effect of the capping ligands. Note that the peak postion of the ligand emission was found to vary with the heating temperatue. 5

6 Figure S4. TEM images and emission spectra for Eu 3+ activators in NaYF 4 and NaGdF 4 host, respectively. Scale bars for TEM images are 100 nm. The results reveal a much higher sensitization efficiency in NaGdF 4 host than in NaYF 4 host, suggesting that Gd sublattice facilitates the energy transfer from Ce 3+ to Eu 3+. 6

7 Figure S5. TEM images and emission spectra for Tb 3+ activators in NaYF 4 and NaGdF 4 host, respectively. Scale bars for TEM images are 100 nm. The results reveal a much higher sensitization efficiency in NaGdF 4 host than in NaYF 4 host, suggesting that Gd sublattice facilitates the energy transfer from Ce 3+ to Tb 3+. 7

8 Figure S6. Simplified energy level diagram showing the proposed energy transfer mechanism and optical transitions in the nanostructures. 8

9 Figure S7. TEM images and emission spetra for Nd 3+ activators in NaYF 4 and NaGdF 4 host, respectively. Scale bars for TEM images are 100 nm. The spectra were compiled from two parts recorded with Hamamatsu R928P ( UV to visible) and R (visible to NIR) PMTs, respectively. Note that Tb 3+ ions are intentionally doped to provide an internal reference for compiling the spectra due to the instinctively high energy transferr effecency from Ce 3+ to Tb 3+. The dominant emission of Nd 3+ in NaGdF 4 host suggests that Gd sublattice can mediatee a highly efficient energy transfer from Ce 3+ to Nd 3+, which was observed for the first time to the best of our knowledge. 9

10 Figure S8. Emission spectrum of NaGdF 4 :Nd(2%)@NaGdF 4 :Ce(15%) nanoparticles. The characteristic emission peaks originating from 4 D 3 state of Nd 3+ are owing to eliminated cross relaxations. The strong peak intensities suggest an efficient sensitization process. 10

11 Figure S9. TEM images and emission spectrum of core shell shell nanopar cles dually ac vated with Eu 3+ and Tb 3+ at low dopant concentrations. Scale bars for TEM images are 100 nm. The nanoparticles give rise to quasi continuous emission spanning from UV to visible spectral range due to largely eliminated cross relaxations. 11

12 Figure S10. TEM images and emission spectrum for the multishell nanoparticle encoded with Yb 3+, Er 3+, Eu 3+, Tb 3+, and Nd 3+ at separate layers. Scale bars for TEM images are 100 nm. Upon single wavelength excitation at 250 nm, the nanoparticles show full spectrum emission spanning from UV to NIR, due to controlled energy cascade within the nanoparticles. Notably, a large Stokes shift of more than 1300 nm was realized. 12

13 Figure S11. TEM images and emission spectra of NaGdF 4 :Yb/Er(50/5%)@NaGdF 4 4 :Ce(15%) nanoparticles. Scale bars for TEM images are 100 nm. The nanoparticles show distinct optical emissions in response to excitation of different wavelength, due to vastly available electronic transitions offered by different dopant ions. Note that the UV light source for the luminescence photos in the insets was a hand held UV lamp (254 nm) ). 13

14 Figure 12. Evaluation of the photochemical stability of the the nanoparticle ink. The optical emission is enssentially unaltered after the anti countfreiting pattern is exposed to ambient light for six months, demonstrating fairly robust properties of the nanoparticles. 14

15 Figure S13. Control experiments demonstrating energy cascade across two set of nanoparticles comprising the sensitizer and activator, respectively. The concentrated donor and accepter nanoparticle dispersions (1 wt %) individually display no visible emission under deep UV excitation. Upon mixing, visible emission can be clearly observed due to inter particle energy cascade. 15