Supporting Information for:
Getting to the (Square) Root of the Problem:
How to Make Non-Coherent Pumped
Upconversion Linear
Alexandre Haefele, Jörg Blumhoff, Rony S. Khnayzer, and Felix N. Castellano*
Department of Chemistry and Center for Photochemical Sciences, Bowling Green State
University, Bowling Green, Ohio 43403
E-mail: castell@bgsu.edu
S1 Materials
PdOEP and DPA were obtained from Frontier Scientific and Aldrich Chemical Company,
respectively, and used without further purification. Spectroscopic grade toluene was obtained
from Aldrich.
Spectroscopic Measurements
Static absorption spectra were measured with a Cary 50 Bio UV-Vis spectrophotometer from
Varian. Steady-state luminescence spectra were obtained on a FL/FS920 from Edinburgh
Instruments or with a PTI Instruments spectrofluorimeter, achieving excitation with a 450 W or a
75 W Xe arc lamp, respectively. Excitation power was measured using a Nova II/PD300-UV
power meter/detector head from Ophir. In experiments utilizing monochromatic laser excitation,
the 514.5 nm line from an Ar+ laser (Coherent, Innova 300) was isolated using a bandpass filter.
In all experiments, different excitation powers were realized by using a series of neutral density
filters. Single wavelength emission intensity decays were acquired with a N2 pumped dye laser
(2-3 nm fwhm) from PTI (GL-3300 N2 laser, GL-301 dye laser). Coumarin 500 was used to tune
the unfocused pulsed excitation beam to selectively excite PdOEP. All luminescence samples
were prepared either in 1 cm2 anaerobic quartz cells purchased from Starna Cells or in a specially
designed 1 cm2 optical cell bearing a side arm round bottom flask and were either deoxygenated
for at least 30 minutes with high purity argon or subjected to a minimum of three freeze-pumpthaw cycles (8-10 µ vacuum) prior to all measurements.
Stern-Volmer Quenching
The Stern-Volmer (KSV) and the bimolecular quenching constants (kq) were obtained according
to the dynamic Stern-Volmer relation, τ0/τ = 1 + KSV[Q], where τ0 and τ are the PdOEP lifetimes
in the absence or presence of the quencher, respectively. KSV is the Stern-Volmer constant, KSV =
kqτ0, and [Q] is the molar concentration of DPA. The Stern-Volmer slope was linear over the
entire range of quencher concentrations.
S2 Figure S1. Absorption spectra of the samples used for the Stern-Volmer measurements in
toluene.
Figure S2. Luminescence intensity decay profiles of PdOEP measured as a function of DPA
concentration in deareated toluene (C500 laser dye, emission detected at 665 nm).
S3 Figure S3. Stern-Volmer plot generated from lifetime quenching of PdOEP with DPA in
deareated toluene, using the single exponential fits to the data set from Figure S2.
S4 Power Dependence with Coherent Photons
For this experiment, a bandpass filter (514.5 nm) was used to filter the excitation beam and
upconversion intensities at 420 ± 6 nm were recorded over one minute in time-based mode and
averaged. For higher excitation powers, the use of neutral density filters prior to the detector was
necessary to prevent PMT saturation. The final emission intensities in the latter samples were
corrected for the filter transmittance at 420 nm.
Figure S4. Absorption spectrum of the PdOEP/DPA sample used for the power dependence
measurements with laser excitation. The inset represents a zoom-in of the area of excitation (λexc
= 514.5 nm) centered on the first Q-band.
S5 Figure S5. Normalized upconversion intensities at 420 nm plotted as a function of the incident
laser power density in the weak annihilation region, 7.2 - 30.6 mW/cm2. The inserted function on
the graph, y = x2 (blue), indicates the incident quadratic dependence in the low power regime of
this experiment. This is the same data as presented in Figure 2.
Figure S6. Normalized upconversion intensities at 420 nm plotted as a function of the incident
laser power density in the strong annihilation region, 1.8-12.6 W/cm2. The inserted function on
the graph, y = x (black), indicates linear dependence in the high power regime. This is the same
data as presented in Figure 2.
S6 Power Dependence with Non-Coherent Photons
Figure S7. Absorption spectrum of the PdOEP/DPA sample used for power dependence
measurements with non-coherent excitation. The inset represents a zoom-in of the Q-band region
indicating the 3 wavelengths of excitation in Figure 3 (λex = 515, 530 and 545 nm).
Figure S8. Example of the upconverted emission intensity profile of DPA in toluene following
selective excitation of PdOEP (λex = 545 nm/455 nm long pass filter, O.D. = 0.29) measured as a
function of incident light power density. Upconversion initiates under these experimental
conditions at a power density of 140 µW/cm2.
S7 Figure S9. Sun (AM 1.5) irradiance as a function of wavelength as obtained from NREL.1 The
integrated irradiance supplied by the sun across the absorption spectrum of the PdOEP sensitizer
(475-575 nm, green area) is 13 mW cm-2.
Figure S10. Photon flux from the sun (AM 1.5) as a function of wavelength as calculated from
Figure S9. The integrated photon flux supplied by the sun across the absorption spectrum of the
PdOEP sensitizer (475-575 nm, green area) is ~ 3.5×1016 photons cm-2 s-1.
Reference
1
National Renewable Energy Laboratory (NREL), MS ExcelTM spreadsheet file
downloaded from <http://rredc.nrel.gov/solar/spectra/am1.5/>.
S8