An improved experimental determination of external photoluminescence quantum efficiency

Abstract

Measurements of the photoluminescence (PL) quantum yield of high refractive index samples, such as thin films of polymeric semiconductors, are problematic owing to difficulties in determining the angular distribution of the emission, reflectivity, and absorbance. In the context of conjugated polymers, there is great interest in establishing the absolute quantum efficiency for PL as this is considered to determine the limits to the efficiency of electroluminescent diodes. A quantitative measurement of external PL efficiency is useful for a number of other reasons. For instance, in conjunction with time-resolved PL measurements, it provides a means of determining the radiative and nonradiative decay constants.'']The external radiative quantum efficiency, q, is defined by Equation 1. number of photons emitted ' = number of photons absorbed PL efficiency measurements in solution are relatively simple becausc it is usually appropriate to assume an isotropic angular distribution for the emission. However, this is not true for thin solid films. For molecular and polymeric materials, anisotropy in the distribution of chromophores leads to an anisotropy in the emission dipole-moment. In addition, wave-guiding effects also modify the angular dis-

Electronic spectral and photophysical properties of some p-phenylenevinylene oligomers in solution and thin films

“…The solid-state photoluminescence quantum yields in thin films were obtained with this integrating sphere, using the method outlined by de Mello et al [27] and applied by Palsson and Monkman [28] to polypyridine films using a set-up similar to the used in this work.…”

Photophysics and Photocurrent Generation in Polythiophene/Polyfluorene Copolymer Blends

“…PL spectra and efficiencies were measured at room temperature in a nitrogen-purged integrating sphere with excitation from an argon ion laser at 488 nm and detection with an Oriel Instaspec IV spectrometer. PL efficiencies were calculated as described by de Mello et al [30]. Time-correlated single photon counting (TCPSC) data were obtained using a 470-nm diode laser (PicoQuant LDH 400) with an 80-ps full width at half maximum at a 10 MHz repetition rate.…”

Substituent Effects on the Fluorescence Properties of ortho‐Carbor­anes: Unusual Emission Behaviour in C‐(2′‐Pyridyl)‐ortho‐carboranes

“…The quantum yields in solution were determined against the standard POPOP [1,4-bis(5-phenyloxazol-2-yl)benzene, Φ = 0.93], while quantum yields of the thin films were determined with the integration-sphere setup according to the Mello method. [76] The emission of a thin film was measured in the integration sphere with excitation at 290 nm. The sample was placed in the centre of the sphere where direct excitation takes place for the first measurement (index: X_in).…”