ISO 20351:2017

Fine ceramics (advanced ceramics, advanced technical ceramics) - Absolute measurement of internal quantum efficiency of phosphors for white light emitting diodes using an integrating sphere

ISO 20351:2017 specifies a method of absolute measurement (using an integrating sphere) of internal quantum efficiency of phosphor powders which are excited by UV or blue light and emit visible light, and which are used for white light-emitting diodes (LEDs). ISO 20351:2017 can be adopted for the measurement of phosphors used in non-white LEDs, for example, green, orange, pink or purple LEDs.

Céramiques fines (céramiques avancées, céramiques techniques avancées) — Mesurage absolu du rendement quantique interne des luminophores des diodes électroluminescentes blanches en utilisant une sphère intégrante

General Information

• Status: Published
• Publication Date: 07-Sep-2017
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: ISO/TC 206 - Fine ceramics
• Drafting Committee: ISO/TC 206/WG 11 - Electrical and optical applications
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 16-Oct-2024
• Completion Date: 13-Dec-2025

Relations

• Consolidated By: ISO 6540:2021 - Maize - Determination of moisture content (on milled grains and on whole grains)
• Effective Date: 06-Jun-2022
• Revised: ISO 20351:2024 - Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for optical properties of ceramic phosphors for white light-emitting diodes using an integrating sphere
• Effective Date: 29-Apr-2023

Overview - ISO 20351:2017 (Integrating sphere method for phosphor IQE)

ISO 20351:2017 specifies an absolute measurement method for the internal quantum efficiency (IQE) of phosphor powders used in white light-emitting diodes (LEDs), using an integrating sphere. The procedure targets phosphors excited by UV or blue light that emit visible light, and it can also be applied to phosphors for non-white LEDs (green, orange, pink, purple). The standard documents equipment configuration, calibration, sample preparation, measurement steps, calculations and reporting to reduce inter-lab variation in measured photoluminescence quantum efficiency.

Key topics and technical requirements

• Measurement principle: Absolute IQE measurement using an integrating sphere to capture excitation, emission and scattered light for photon-based calculations.
• Equipment configuration: Describes a light source unit (monochromator or laser), sample unit (cell and integrating sphere), detecting unit (spectrometer, detector, optics) and data processing.
• Optical requirements: Guidance on excitation spectral width (desirable half-width < 15 nm), beam diameter relative to sample area, and minimum sample thickness (at least 2 mm).
• Sample handling: Storage, pre-processing and filling of cells; use of cover glasses or lids; use of reference cells or white diffusers (e.g., barium sulfate or PTFE) for baseline measurements.
• Calibration & maintenance: Wavelength calibration of source and detector, spectral responsivity correction, maintenance of sphere walls and white diffusers to ensure stable reflectance.
• Measurement procedure: Steps for measuring light spectrum with and without the phosphor sample, handling secondary absorption and self-absorption effects.
• Calculations: Conversion to photon-number-based spectra, derivation of photoluminescence spectra, determination of relative absorbed and emitted photon numbers and calculation of internal quantum efficiency.
• Reporting: Requirements for documenting methods, equipment, conditions and results to support reproducibility.

Applications and who uses this standard

• Phosphor manufacturers and material scientists validating photoluminescence quantum efficiency of powders for LED lighting.
• LED device and lamp manufacturers assessing phosphor performance for white and colored LEDs.
• Test laboratories and quality-control teams performing standardized IQE measurements for product specification and R&D benchmarking.
• Researchers in solid-state lighting (SSL) and fine ceramics focusing on advanced ceramic phosphors.

Related standards

• Normative reference: CIE S 017/E:2011 (International Lighting Vocabulary).
• ISO/TC 206 work context: part of fine ceramics and advanced materials standards for LED component testing.

Keywords: ISO 20351:2017, internal quantum efficiency, integrating sphere, phosphor powders, white LED, photoluminescence quantum efficiency, IQE measurement, fluorescence spectrophotometer.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20351
First edition
2017-09
Fine ceramics (advanced ceramics,
advanced technical ceramics) —
Absolute measurement of internal
quantum efficiency of phosphors for
white light emitting diodes using an
integrating sphere
Céramiques fines (céramiques avancées, céramiques techniques
avancées) — Mesurage absolu du rendement quantique interne des
luminophores des diodes électroluminescentes blanches en utilisant
une sphère intégrante
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measuring equipment . 2
4.1 Equipment configuration . 2
4.2 Light source unit . 3
4.3 Sample unit . 3
4.3.1 Cell . 3
4.3.2 White diffuser or reference cell . 4
4.3.3 Integrating sphere . 4
4.4 Detecting unit . 4
4.4.1 Directing optics . 4
4.4.2 Spectrometer and detector . 4
4.4.3 Amplifier . 4
4.5 Signal and data processing unit . 4
5 Calibration, checking and maintenance of measuring equipment .5
5.1 General . 5
5.2 Wavelength calibration of light source unit . 5
5.3 Cells and cover glasses . 5
5.4 Integrating sphere walls and white diffusers . 5
5.5 Wavelength calibration of detecting unit . 5
5.6 Spectral responsivity correction . 5
6 Samples . 5
6.1 Storage and pre-processing . 5
6.2 Filling cells with samples . 5
7 Measurement methods . 6
7.1 Measurement environment. 6
7.2 Light spectrum without phosphor sample . 6
7.3 Light spectrum with phosphor sample . 6
8 Calculations. 6
8.1 Conversion to photon-number-based spectra . 6
8.2 Photoluminescence spectrum . 7
8.2.1 General. 7
8.2.2 Method 1 . 7
8.2.3 Method 2 . 7
8.3 Internal quantum efficiency . 7
8.3.1 Relative number of absorbed photons . 7
8.3.2 Relative number of photoluminescent photons. 8
8.3.3 Internal quantum efficiency . 8
9 Report . 8
Bibliography .10
Foreword
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described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
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This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
iv © ISO 2017 – All rights reserved

Introduction
White light-emitting diode (LED) based solid-state lighting (SSL) has been widely used for a variety
of applications as alternatives for incandescent and fluorescent lamps. In the beginning, white LEDs
(comprising blue LEDs and yellow phosphors) became popular as backlight sources for small-size
liquid-crystal displays (LCDs) used in mobile phones and digital cameras. These were followed by white
LEDs (consisting of blue LEDs combined with green and red phosphors) applied to backlight sources
for large-area LCDs. Subsequently, LED lamps have been commercialized for general lighting, replacing
conventional luminaires and capitalizing on their advantages, such as compactness, high luminous
efficiency, high brightness below 0 °C or higher ambient temperatures, long life, and controllability of
light intensity and colour temperature.
The optical performance of a phosphor for use in a white LED is one of the most important factors
influencing the performance of the white LED. Accordingly, it is of great importance, not only for
researchers and manufacturers of phosphors for use in white LEDs but also for researchers and
manufacturers of white LED devices, to evaluate the optical properties of the phosphors in a well-
established manner. However, standard measurement methods of studying the optical properties of
luminescent powder materials commercially used for white LEDs have never been developed.
Photoluminescence quantum efficiency is one of the key parameters of phosphors for use in white LEDs
and has been measured extensively by using an integrating sphere-based absolute method. This method
was originally developed to determine the photoluminescence quantum efficiency for fluorophore-
doped organic thin films and solutions, and has also been applied to phosphor powders. However,
those who measure the quantum efficiency of phosphor materials have frequently noted that the
measured quantum efficiency may deviate beyond their tolerance level, depending on the measurement
equipment, the geometrical configuration of the integrating sphere and the arrangement of the sample
cell, even if the measurement procedure is common in principle. This document provides the absolute
measurement method of internal quantum efficiency of phosphors for use in white LEDs with reduced
deviation of measured values. In this document, measurement equipment and procedures, which can be
the sources of the deviation, are described in detail, helping those who address the high performance
phosphors for competitive SSL products to obtain the proper information on their competitiveness.
INTERNATIONAL STANDARD ISO 20351:2017(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Absolute measurement of internal quantum
efficiency of phosphors for white light emitting diodes
using an integrating sphere
1 Scope
This document specifies a method of absolute measurement (using an integrating sphere) of internal
quantum efficiency of phosphor powders which are excited by UV or blue light and emit visible light,
and which are used for white light-emitting diodes (LEDs).
This document can be adopted for the measurement of phosphors used in non-white LEDs, for example,
green, orange, pink or purple LEDs.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
CIE S 017/E:2011, International Lighting Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in CIE S 017/E:2011 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
internal quantum efficiency
ratio of the number of photons emitted in free space from the phosphor to the number of excitation
light photons absorbed by the phosphor
3.2
cell
container filled with a sample or a white material such as barium sulfate
Note 1 to entry: A cell is typically a flat plate sample holder with a cylindrical hollow, a Petri dish or a rectangular
cell used in a spectrophotometer.
3.3
reference cell
cell (3.2) filled with a white powder which has a high spectral diffuse reflectance over the whole visible
spectrum (such as barium sulfate or alumina), used when measuring the excitation light spectrum
3.4
white diffuser
white plate which has a high spectral diffuse reflectance over the whole visible spectrum [suc
...