Photoluminescence of the integrating sphere walls, its influence on the absolute quantum yield measurements and correction methods

Jan Valenta

doi:10.1063/1.5052601

Abstract

Determination of the absolute quantum yield (QY) of photoluminescence (PL) or electroluminescence is commonly performed using an integrating sphere (IS) – versatile device for radiometry applications. The key feature of IS is very high diffused reflectance of its internal surface. Two materials are commonly used: (a) the sintered high-density polytetrafluoroethylene (Spectralon) and (b) materials based on barium sulphate (Spectraflect). Using PL-micro-spectroscopy we show that both materials reveal PL from localized centers excitable by UV, blue and green light emitting broad PL spectrum extending up to the red spectral region. The main effect of PL from IS-walls is introduction of non-constant parasitic background which is mixed with PL from a tested sample during the QY measurements. We develop theoretical description of QY determination which includes effects of PL from IS walls. This allows us to propose and test a reliable and universal correction for the IS-related PL background. Finally, a method of “black sample” is proposed and applied to estimate PL QY of Spectraflect which is shown to decrease from 0.09 to 0.015% for excitation shift from 320 to 440 nm.

Highlights

Absolute quantum yield (QY) determination using an integrating sphere (IS) is well established method whose main advantage is independence on the use of a QY-standard, sample scattering and emission polarization.[1]
It plays two roles which are understandable in case of a flat solid sample placed on the IS wall: (a) Semitransparent port – The sample with area STS and absorptance aTS placed anywhere on the IS wall influences the sphere multiplier M as a port with reflectance ρis·(1- aTS)[2]
In a typical experiment the standard deviation of the IS output measurement is about 1% or more, the absorptance of sample inside IS must be at least ∼2.5% which is achieved for single pass absorptance of slightly above 1% and ∼9% for direct and indirect excitation, respectively

Summary

Introduction

Absolute quantum yield (QY) determination using an integrating sphere (IS) is well established method whose main advantage is independence on the use of a QY-standard, sample scattering and emission polarization.[1] An integrating sphere is a spherical cavity with highly-reflective (diffusive) surfaces that enable spatial integration of incoming light flux. It is widely applied in radiometry, photometry and other optical experiments.[2] Internal walls of IS are made of materials with the highest. PL of PTFE materials was attributed to organic contamination and some procedures (sanding and baking) were proposed to reduce PL intensity.[7]

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