Quantification of Anisotropy-Related Uncertainties in Relative Photoluminescence Quantum Yield Measurements of Nanomaterials – Semiconductor Quantum Dots and Rods

Abstract

Abstract:In order to assess the anisotropy-related uncertainties of relatively determined photoluminescence quantum yields ( PL ) of molecular emitters and luminescent nanomaterials, we compared PL values measured without and with polarizers using magic angle conditions and studied systematically the dependence of the detected emission intensity on the polarizer settings for samples of varying anisotropy. This includes a dispersion of a spherical quantum dot (QD) with an ideally isotropic emission, a solution of a common small organic dye in a fluid solvent as well as dispersions of elongated quantum dot rods (QDR) with an anisotropic luminescence and a small organic dye in a rigid polymeric matrix, as ideally anisotropic emitter. Our results show that for instruments lacking polarizers, anisotropy-related measurement uncertainties of relative photoluminescence quantum yields can amount to more than 40%, with the size of these systematic errors depending on the difference in emission anisotropy between the sample and the standard.

pH and concentration dependence of the optical properties of thiol-capped CdTe nanocrystals in water and D2O

“…Steady state PL measurements were performed with a calibrated FLS-920 fluorometer (Edinburgh Photonics) at BAM, equipped with a Xe lamp, Czerny-Turner double monochromators, a reference channel, and Glan-Thompson polarizers placed in the excitation and emission channels set to 0° and 54.7°, respectively (magic angle conditions) to render detected emission intensities independent of possible emission anisotropies. [33][34][35] All fluorescence spectra shown were corrected for the wavelength-dependent spectral responsivity of the fluorometer´s detection channel as previously reported. 36 The relative determination of PL QY from the absorption spectra and integrated corrected emission spectra (blank and spectral correction; consideration of the photonic nature of the emitted light) of the sample and standard in air-saturated solution was performed according to a previously published protocol.…”

Excitation wavelength dependence of the photoluminescence quantum yield and decay behavior of CdSe/CdS quantum dot/quantum rods with different aspect ratios

“…So-called magic-angle conditions were applied (excitation and emission polarizers set to 0° and 54.7°, respectively) to render detected emission intensities independent of sample emission anisotropy. 18,42 For the steadystate measurements (emission spectra) the device-intern xenon lamp was used for sample excitation, whereas for the timecorrelated single photon counting (TPSPC) measurements (PL decays) a pulsed SC400-PP supercontinuum fiber laser (Fianium) with a pulse width of < 1 ns was used as excitation light source. All presented emission spectra were corrected for blank emission (blank correction) and the wavelength dependence of the instrument's spectral responsivity (spectral correction).…”

“…15,16 In addition, their emission is anisotropic or polarized, whereas the photoluminescence (PL) from QDs is isotropic. 17,18 Hence, in the last years, QDQRs have increasingly replaced QDs, and many of the commercially available II/VI semiconductor nanocrystals (SCNCs) or materials incorporated into SCNC-based products are nowadays QDQRs with typical aspect ratios of up to about five. 19,20 For QDs and QDQRs, the size of the spectroscopic key parameter ΦPL 21 is particularly relevant as this value provides also a direct measure for particle and shell quality.…”

“…31 Also photobrightening, especially upon UV excitation using high excitation power densities can be encountered. 16 Moreover, QDQRs can reveal a considerable emission anisotropy especially for larger aspect ratios; requiring the use of polarizers (magic angle conditions) to prevent polarizationrelated artefacts, 18 and the consideration of scattered excitation light, 26,27 particularly for QDQRs of larger aspect ratios can become mandatory. Furthermore, for all data relying on comparisons of PL excitation and wavelength dependent absorption factors, the wavelength dependence of the spectral photon flux reaching the sample (excitation correction curve) and its uncertainty, 31, 39, 40 must be properly considered.…”

Progress in laser cooling semiconductor nanocrystals and nanostructures

“…Furthermore, polarization sensitivities associated with anisotropic nanostructures as well as potential light scattering effects complicate measurements 87,88 . Finally, solvent light scattering and (possibly) fluorescence contribute to measurement errors 85,89 .…”