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: 9060 - Close of review
• Start Date: 03-Mar-2028

Relations

• Consolidated By: ISO 6540:2021 - Maize — Determination of moisture content (on milled grains and on whole grains)
• Effective Date: 06-Jun-2022

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 20351:2017(E)
ISO 2017
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ISO 20351:2017(E)
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© ISO 2017, Published in Switzerland

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ii © ISO 2017 – All rights reserved
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ISO 20351:2017(E)
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

© ISO 2017 – All rights reserved iii
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ISO 20351:2017(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

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organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

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URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
iv © ISO 2017 – All rights reserved
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ISO 20351:2017(E)
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.

© ISO 2017 – All rights reserved v
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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

...