# Influence of Measurement Geometry and Blank on Absolute Measurements of Photoluminescence Quantum Yields of Scattering Luminescent Films

## TL;DR

This paper investigates how measurement setup and blank choice affect the accuracy of photoluminescence quantum yield measurements in scattering films.

## Contribution

The study identifies systematic errors in integrating sphere setups and provides guidelines for accurate quantum yield measurements.

## Key findings

- Center-mounted samples and transparent blanks can cause systematic errors in quantum yield measurements.
- Strongly scattering samples may lead to under- or overestimation of absorbed photon flux.
- Matching the blank's scattering properties to the sample improves measurement accuracy.

## Abstract

For a series of 500
μm-thick polyurethane films
containing
different concentrations of luminescent and scattering YAG:Ce microparticles,
we systematically explored and quantified pitfalls of absolute measurements
of photoluminescence quantum yields (Φf) for often
employed integrating sphere (IS) geometries, where the sample is placed
either on a sample holder at the bottom of the IS surface or mounted
in the IS center. Thereby, the influence of detection and illumination
geometry and sample position was examined using blanks with various
scattering properties for measuring the number of photons absorbed
by the sample. Our results reveal that (i) setup configurations where
the scattering sample is mounted in the IS center and (ii) transparent
blanks can introduce systematic errors in absolute Φf measurements. For strongly scattering, luminescent samples, this
can result in either an under- or overestimation of the absorbed photon
flux and hence an under- or overestimation of Φf.
The size of these uncertainties depends on the scattering properties
of the sample and instrument parameters, such as sample position,
IS size, wavelength-dependent reflectivity of the IS surface coating,
and port configuration. For accurate and reliable absolute Φf measurements, we recommend (i) a blank with scattering properties
closely matching those of the sample to realize similar distributions
of the diffusely scattered excitation photons within the IS, and (ii)
a sufficiently high sample absorption at the excitation wavelength.
For IS setups with center-mounted samples, measurement geometries
should be utilized that prevent the loss of excitation photons by
reflections from the sample out of the IS.