Supporting Information The Effect of Temperature and Gold Nanoparticle Interaction on the Lifetime and Luminescence of Upconverting Nanoparticles

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1 Supporting Information Synthesis and Characterization Supporting Information The Effect of Temperature and Gold Nanoparticle Interaction on the Lifetime and Luminescence of Upconverting Nanoparticles Ali Rafiei Miandashti, 1 Martin E. Kordesch, 2 and Hugh H. Richardson 1 * 1 Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio Department of Physics and Astronomy, Ohio University, Athens, Ohio *richardh@ohio.edu Instrumentation The hexagonal nanostructures of the NaYF4:Yb 3+ : Er 3+ (UCNPs) and gold seeds (GNPs) were characterized by JEOL 1010 transmission electron microscope (TEM). The luminescence emission of UCNPs during attachment of seeds and growth procedure was recorded by a photon technology international (PTI) instrument. Time-Resolved fluorescence data was collected through confocal mode of a WITec α-snom300s microscope where the emission was collected through a built-in APD. The data was recorded through LabVIEW program and a D/A converter. In order to remove the noise, the data was further processed by MATLAB. Microsecond pulsed infrared laser was provided by triggering a 980 nm Dragon Laser for infrared excitation of upconverting nanoparticles. Growth of Gold Nanoparticles on UCNPs; To grow GNPs on the surface of UCNPs, we added 1 ml of an aqueous solution of HAuCl4 3H2O (0.01 M) and 0.5 ml of ascorbic acid (0.1 M) as a mild reducing agent to the solution of UCNP/GNPs. The growth of GNPs on the surface of UCNPs was carried out in situ during the collection of emission spectra. Characterization; After synthesis of β-phase hexagonal NaYF4:Yb3+: Er3+ according to the literature. 1 The TEM and HRTEM of decorated NaYF4:Yb 3+ : Er 3+ nanocrystal is given in figure S1. The energy dispersive X-ray spectrum of UCNP decorated with gold nanoparticle was also recorded in EDS mode of JEM 2100F instrument. Figure S1d shows the corresponding elemental mapping and peaks for Na, Y, F, Yb, Er and Au elements. Due to the minor presence of Er in the structures Formatted: Font: 12 pt, Bold Formatted: Font: 12 pt, Bold Formatted: Font: 12 pt Formatted: Font: 12 pt

2 which is 2 percent of the whole NaYF4:Yb 3+ : Er 3+ nanocrystal, as oppose to other elements. Other elements have been pronounced strongly in the EDS spectrum. S1 a) TEM image of β-phase hexagonal NaYF4:Yb 3+ : Er 3+ upconverting nanoparticle b and c) HRTEM image of hexagonal NaYF4:Yb 3+ : Er 3+ upconverting nanoparticles decorated with gold nanoparticles with different magnifications, d) Elemental mapping of NaYF4:Yb 3+ : Er 3+ nanocrystal e) EDS spectrum of NaYF4:Yb 3+ : Er 3+ nanocrystals shown in d.

3 Enhancement and Quenching; NaYF4:Yb 3+ : Er 3+ nanocrystals show enhancement and quenching when interact with gold nanoparticles. We monitored the enhancement and quenching of emission of UCNPs as the seeds were attached to the surface gradually. Figure S2(a-c) shows the TEM images corresponding to starting NaYF4:Yb 3+ : Er 3+ nanocrystals, NaYF4:Yb 3+ : Er 3+ nanocrystals decorated with gold nanoparticles and NaYF4:Yb 3+ : Er 3+ nanocrystals decorated with gold nanoparticles after the growth phase. As the experiment progresses, the spectra was recorded using a PTI instrument where the excitation wavelength was set to 980 nm and the spectra was collected over a period of two hours (See Figure S2 (d, e). Figure S2 (f) shows the extinction spectrum of UCNP/GNP (black) and UCNP (red) in aqueous solution. The surface plasmon resonance of gold nanoparticles is located in the green band region of upconverting nanoparticles. Figure S2 (g) extracted from d shows the enhancement of emission of UCNPs as more and more gold nanoparticle seeds are attached to the surface. S2 (h) plotted from e also shows the decrease in the emission intensity of UCNP/GNPs as previously attached seeds grow and turn into larger particles.

4 S2. a-c) TEM images of starting NaYF4:Yb 3+ : Er 3+ nanocrystals, NaYF4:Yb 3+ : Er 3+ nanocrystals decorated with gold nanoparticles and NaYF4:Yb 3+ : Er 3+ nanocrystals decorated with gold nanoparticles after the growth phase, respectively d) Enhancement of H and S bands as more gold nanoparticle seeds attach to UCNPs, e) Quenching of H and S bands as gold nanoparticle seeds grow upon addition of Au 3+ ions to decorated UCNPs. f) The extinction spectrum of UCNP/GNP (black) and UCNP (red) in aqueous solution g) Enhancement and quenching of emission of β-phase hexagonal NaYF4:Yb 3+ : Er 3+ upon attachment of GNPs seeds h) Quenching the emission of β-phase NaYF4:Yb 3+ : Er 3+ nanocrystals during the growth of seeds. Measurement of Temperature; The luminescence emission of upconverting nanoparticles is shown in Figure S3. The emission spectrum shows four different bands in blue, green and red regions. The emission bands in green

5 region, which are 2 H 11/2 4 I 15/2 and 4 S 3/2 4 I 15/2 bands, are thermally coupled and the ratio of the peaks depend on temperature. S3. Luminescence emission of NaYF4:Yb 3+ : Er 3+ nanocrystals showing four emission bands in blue, green and red regions. Figure S4 (a) shows the luminescence spectrum in the green region, known as H and S bands. Calculation of temperature based on luminescence emission has been previously introduced. 2 In this approach, we used the green band emissions (H and S bands) to calculate temperature for UCNPs and UCNP/GNPs under different temperatures. The temperature of the nanoparticles was changed using a Peltier where the temperature changed from 0 to 100 C and it was monitored by a thermocouple. As figure S4 (a) shows, at higher temperatures we observe an increase in the intensity of H band and a decrease in the intensity of S band. Therefore the ratio of H band to S band can be used as criteria to calculate the temperature. Also, we observed a small difference in the S band peak shape with temperature that is attributed to a slight broadening of the peaks at higher temperatures and underlying peaks that do not change with temperature (see twodimensional correlation analysis in S6). The underlying peaks that are invariant with temperature are shown as solid red lines in figure S6. By having the ratio of H band to S band and the Boltzmann s equation ( HH = AAAAAAAA ( ΔΔΔΔ )) where A is the pre-exponential factor and ΔE is an SS kkkk energy difference between the H band ( 2 H 11/2 4 I 15/2 transition) and the S band ( 4 S 3/2 4 I 15/2 transition), and k as Boltzmann s constant, we calculated the temperature. The pre-exponential factor, A is defined from fitting the best linear fit to the scattering plot of natural logarithm of H/S versus 1/T. By taking the relative peak areas of H and S bands at various temperatures, we can plot the calibration curve and use it for our temperature measurements, Figure S4 (b). shows that the slope of the calibration curve is equals to ΔE/k, and we use the value of 996 ± 65 and pre-exponential factor A,1.4 ± 0.2 for the rest of temperature calculations. The uncertainty in calculation of temperature, ± 8.5 K is due to the fluctuations of peak intensities and it can be

6 improved by increasing the integration time of data collection. We produced figure 5 from the ratio of signal and not the spectrum intensities in order to stay consistent with the data collected for time resolved data as well as quantum yield calculations. S4. a) Green band emission of UCNPs under 980 nm laser illumination at two different temperatures b) Calibration plot of UCNP emission between the ranges of 0 to 100 C. Two-Dimensional Correlation Analysis Visible emission spectra exciting at 980 nm are collected as a function of temperature. The spectra are first normalized with respect to integrated band area for the entire spectrum. Then, the spectra are mean centered and a two-dimensional correlation analysis performed using Hilbert transformation. 3 Figure S5a shows the two-dimensional correlation map from an analysis of the green spectral region ( nm). The H bands ( 2 H 11/2 4 I 15/2 transition) are located at nm and the S bands ( 4 S 3/2 4 I 15/2 transitions) are located at nm. A negative correlation is observed between the H and S bands. This correlation relationship indicates that the H and S bands are correlated but are moving in opposite directions. The diagonal elements of the correlation matrix are shown in Figure S5b. The largest spectral variations with temperature are observed at 520 nm and 540 nm and the peak shape is slightly different (S band region) than the spectrum shown in figure S4a. This difference suggests that there are peaks in the emission spectrum that contribute to the overall band shape but are not Erbium S bands that change with temperature. The slope in the calibration curve shown in Figure S4b is equal to ΔE/k where ΔE is the energy gap between the H bands and the S bands. The H and S band at 520 and 540 nm respectively has the largest variation in emission as the temperature is changed and these bands make the largest contribution to the slope measured in Figure S4b.

7 Figure S5. a) Two-dimensional correlation analysis of the green emission bands of NaYF4:Yb 3+ : Er 3 UCNPs as temperature is changed from 10 to 90 o C. (b) Diagonal elements of the correlation map shown in Figure 3a. The diagonal elements show the magnitude in the spectral variation with temperature. Figure S6. Peak shape of UCNPs emission at 293 K with curve fitting. The raw data is shown as black squares. The fit is the continuous black line through raw data. The fitted peaks are shown in black (peaks that change with temperature) and red (peaks that do not change with temperature). A two-dimensional correlation analysis is also performed on the temperature dependence in the emission spectrum for the spectral region nm to see if the loss of green band emission is correlated with a gain in the red band emission ( 2 F 5/2 4 I 15/2 transition). The emission spectra are shown in Figure S6a while the correlation map is shown in Figure S6b. A

8 negative correlation is observed between the green bands and red bands confirming that loss in the H and S band is correlated with a gain in the red bands. The energy difference between the green bands and red bands is ~ 3500 cm -1. If a single phonon has the energy of ~ 700 cm -1, then it would take ~ 5 phonons to make the energy gap of 3500 cm -1. Figure S7. a) Normalized Emission spectra taken over the temperature range of 10 to 90 o C. b) Two-dimensional correlation map of spectrum shown in Figure S7a. Time-Resolved Measurement of Luminescence Emission We set up the time-resolved measurement by modulation of a 980 nm Dragon Laser using a pulse generator. For luminescence decay measurements, we adjusted 400 us width pulses with frequency of 500 s -1. For the preparation of samples, the colloidal solution of upconverting nanoparticles were drop casted onto the coverslip and dried before measurements. The response of luminescent nanoparticles to pulse 980 nm was collected through a built-in avalanche photodiode inside WITec microscope. The luminescent response of 2 H 11/2 4 I 15/2 and 4 S 3/2 4 I 15/2 bands to 980 nm pulsed laser was separated through a MonoScan 2000 monochromator. The response of avalanche photodiode was turned into digital signal using an Analog to Digital convertor. The signal was averaged using MATLAB. The Effect of Temperature on Lifetime Decay We recorded the luminescence decay of the emission of decorated and plain UCNPs as a function of temperature. In Figure 4a, we see a relatively linear decrease from 175 to 75 us in the lifetime as a function of temperature for plain UCNPs however, for UCNP/GNPs, since there is a fast and slow component, for each of the components, the trend is different. For the slow component, we see a decrease in the lifetime while for the fast component, no significant change is observed (see S8). We believe that gold decorated UCNP has much more complexity as opposed to plain UCNP and understanding the effect of temperature on individual lifetime components is beyond the scope of this paper.

9 S8. a) Lifetime decay of green bands of UCNPs/GNPs under 980 nm laser illumination between the range of 25 C and 150 C Reference (1) Boyer, J. C.; Cuccia, L. A.; Capobianco, J. A. Synthesis of Colloidal Upconverting NaYF4 : Er3+/Yb3+ and Tm3+/Yb3+ Monodisperse Nanocrystals. Nano Lett. 2007, 7, (2) Fischer, L. H.; Harms, G. S.; Wolfbeis, O. S. Upconverting Nanoparticles for Nanoscale Thermometry. Angew. Chemie-International Ed. 2011, 50, (3) Noda, I. Determination of Two-Dimensional Correlation Spectra Using the Hilbert Transform. Appl. Spectrosc. 2000, 54,