ISO 13915:2023

Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for optical properties of ceramic phosphors for white light-emitting diodes with reference materials

This document specifies a substitution measurement method to measure internal quantum efficiency, external quantum efficiency and absorptance of ceramic phosphor powders, which are used in white light-emitting diodes (LEDs) and emit visible light when excited by UV or blue light. In this method, commercially available measurement equipment, such as a fluorescence spectrophotometer or a spectroradiometer equipped with a monochromatic light source as incident light, are used to measure fluorescence spectra for reference materials whose quantum efficiencies and absorptance have been determined using the methods in ISO 23946 and a phosphor material under test.

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General Information

• Status: Published
• Publication Date: 15-Aug-2023
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: ISO/TC 206 - Fine ceramics
• Drafting Committee: ISO/TC 206 - Fine ceramics
• Current Stage: 6060 - International Standard published
• Start Date: 16-Aug-2023
• Due Date: 01-Apr-2025
• Completion Date: 16-Aug-2023

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 13915
First edition
2023-08
Fine ceramics (advanced ceramics,
advanced technical ceramics) — Test
method for optical properties of
ceramic phosphors for white light-
emitting diodes with reference
materials
Reference number
ISO 13915:2023(E)
© ISO 2023

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ISO 13915:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 13915:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Measurement apparatus . 2
4.1 Apparatus configuration . 2
4.2 Light source unit . 4
4.3 Sample unit . 4
4.3.1 Cell . 4
4.3.2 Sample compartment and cell holder . 5
4.4 Detection unit . 5
4.4.1 Directing optical system . 5
4.4.2 Spectrometer and detector . 5
4.4.3 Amplifier . 5
4.5 Signal and data processing unit . 5
5 Calibration, inspection and maintenance of measurement apparatus .5
5.1 General . 5
5.2 Wavelength calibration of light source unit . 6
5.3 Cells . 6
5.4 Wavelength calibration of detection unit . 6
5.5 Spectral responsivity calibration . 6
6 Samples . 6
6.1 Reference material . 6
6.2 Storage and pre-processing . 6
6.3 Filling cells with phosphor powders . 7
7 Measurement procedures .7
7.1 Measurement environment . 7
7.2 Spectrometer setup for substitution measurement . 7
7.3 Measurement for reference material . 7
7.4 Measurement for phosphor material under test . 7
8 Calculation . 8
8.1 Spectral responsivity correction . 8
8.2 Conversion to photon number-based spectral distribution. 8
8.3 Calculation of scattered light and fluorescence photon numbers . 8
8.4 External quantum efficiency . 10
8.5 Absorptance . 10
8.6 Internal quantum efficiency . 10
9 Test report .10
Annex A (informative) Wavelength correction of monochromators by using phosphor
material with specific fluorescence peaks .12
Annex B (informative) Correction method for chromaticity coordinates of ceramic
phosphors for white light-emitting diodes with reference materials .14
Annex C (informative) Guide to application of relevant ISO documents concerning test
methods for optical properties of ceramic phosphors for white LEDs .15
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ISO 13915:2023(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
committee has been established has the right to be represented on that committee. International
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 13915:2023(E)
Introduction
White light-emitting diode (LED)-based solid-state lighting (SSL) has been widely used for a variety of
applications as an alternative for incandescent and fluorescent lamps. Initially, 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 were commercialised for general lighting, replacing conventional
luminaires and capitalising 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 material 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 optical properties of the phosphors in a well-established
manner. Photoluminescence quantum efficiency is one of the key optical parameters of phosphors for
use in white LEDs and has been measured extensively by using an integrating sphere-based absolute
method.
ISO 20351 was developed in accordance with the demand for standardizing the test method of internal
quantum efficiency of phosphors using an integrating sphere. This standard test method has the
advantage of a short measurement time and being available to those with no expertise in precise optical
measurement. Despite their importance in terms of the performance of ceramic phosphor products,
the external quantum efficiency and absorptance are out of the scope of ISO 20351 due to insufficient
understanding of the source of variation in these measurement values.
ISO 23946 was then developed to provide “integrating-sphere-free” absolute measurement methods for
the external quantum efficiency, internal quantum efficiency and absorptance for ceramic phosphors
for use in white LEDs using a gonio-spectrofluorometer. These goniometric measurement methods are
based on basic illumination theory and can give accurate values of quantum efficiencies and absorptance
for ceramic phosphors regardless of the spatial distribution of fluorescence or scattered light. While
the goniometric method is theoretically rigorous, it requires large and complicated equipment as well
as a long time to complete the measurement. Therefore, the application of ISO 23946 is assumed to be
limited to those who intend to determine the optical properties of phosphor materials to be utilized as
reference materials.
This document provides a simple measurement method for those who use a general-purpose instrument,
where a phosphor material with optical properties evaluated according to the methods in ISO 23946 is
used as a reference material.
In this document, measurement conditions and procedures that can affect the measurement values
are described in detail, helping those who address high-performance phosphors for competitive SSL
products to obtain appropriate information on their competitiveness.
This document can also be adopted for phosphors used in non-white LEDs, e.g. green, orange, pink and
purple.
Guide to application of relevant ISO documents concerning test methods for optical properties of
ceramic phosphors for white LEDs are presented in Annex C.
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INTERNATIONAL STANDARD ISO 13915:2023(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for optical properties of ceramic
phosphors for white light-emitting diodes with reference
materials
1 Scope
This document specifies a substitution measurement method to measure internal quantum efficiency,
external quantum efficiency and absorptance of ceramic phosphor powders, which are used in white
light-emitting diodes (LEDs) and emit visible light when excited by UV or blue light. In this method,
commercially available measurement equipment, such as a fluorescence spectrophotometer or a
spectroradiometer equipped with a monochromatic light source as incident light, are used to measure
fluorescence spectra for reference materials whose quantum efficiencies and absorptance have been
determined using the methods in ISO 23946 and a phosphor material under test.
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.
ISO 20351, 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 23946, Fine ceramics (advanced ceramics, advanced technical ceramics) — Test methods for optical
properties of ceramic phosphors for white light-emitting diodes using a gonio-spectrofluorometer
ISO/CIE 11664-3, Colorimetry — Part 3: CIE tristimulus values
CIE S 017/E, International Lighting Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20351, ISO 23946, CIE S 017/E,
ISO/CIE 11664-3 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
fluorescence spectrophotometer
apparatus measuring the fluorescence spectrum of a sample irradiated on its surface by monochromatic
light
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ISO 13915:2023(E)
4 Measurement apparatus
4.1 Apparatus configuration
The apparatus includes a light source unit, a sample unit, a detection unit and a signal/data processing
unit. Figure 1 and Figure 2 illustrate the typical configurations of a measurement apparatus.
The light source unit generates monochromatic excitation light and comprises a white light source,
a power supply for the white light source, a focusing optical system, a wavelength selection unit
(monochromator for the white light source) and an optical system for irradiation. A collimated laser
beam can also be used as the monochromatic light source.
The sample unit comprises a cell, a sample compartment and a cell holder.
The detection unit comprises a directing optical system for collecting light, a spectrometer, a detector
and an amplifier.
Key
A light source unit 1 light source
B sample unit 2 monochromator
C detection unit 3 optical system for irradiation
 4 sample (cell)
 5 directing optical system
 6 spectrometer
 7 detector
Figure 1 — Typical measurement apparatus configuration (fluorescence spectrophotometer
type)
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ISO 13915:2023(E)
Key
A light source unit 1 light source
B sample unit 2 monochromator
C detection unit 3 optical system for irradiation (optical fibre probe)
 4 sample (cell)
 5 directing optical system (optical fibre probe)
 6 array spectrometer/spectroradiometer
Figure 2 — Typical measurement apparatus configuration (array spectrometer type)
The geometrical condition of the measurement is illustrated in Figure 3. When a substitution
measurement is performed with a certain fixed angle of incidence, an angle-adjustable optical system
for irradiating incident light onto the centre of a sample surface may be used. The propagation vector
of the optical radiation, whether emitted or reflected, is defined as the direction of observation and
should be located in or near the plane of incidence.
The angle of incidence θ (see Figure 3) should be configured with reference to the measurement
i
geometry applied when measuring the quantum efficiencies and absorptance of the reference material
in accordance with ISO 23946.
The angle of observation θ (see Figure 3) shall not be identical with or close to the angle of incidence θ
r i
to avoid specular reflection from the surface of a cell, a cover glass or a glass lid, as well as specular-like
directional scattering from the sample.
The following measurement geometries are typical configurations.
Geometry A θ = 0°, θ = 30°
i r
Geometry B θ = 30°, θ = 60°
i r
Geometry A is a vertical incidence configuration which is applicable to various sets of monochromatic
light sources and spectroradiometers. Geometry B is the basic configuration for commercially available
fluorescence spectrophotometers. Geometries other than these typical geometries are also possible.
A measurement apparatus with the sample unit comprising an integrating sphere, where the specific
angle of observation cannot be defined, is out of the scope of this document. The substitution
measurement can also be performed by an apparatus with an integrating sphere, which is described in
ISO 20351.
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ISO 13915:2023(E)
Key
angle of incidence
θ
i
angle of observation
θ
r
Figure 3 — Geometrical condition of substitution measurement
4.2 Light source unit
The spectral width of the excitation light is limited by the monochromator. The half-width of the
excitation light spectrum should be 15 nm or less.
The excitation light passes through an optical system for irradiation and irradiates a sample. One
example of an optical system for irradiation is focusing optics. The monochromated light from the exit
slit of the monochromator is collimated by the focusing optics to provide a circular, nearly circular or
oval-shaped beam of light onto the sample surface. An optical fibre probe can also be used as the optical
system for irradiation.
The optical system for irradiation should be designed to optimise the size of the illuminated area on the
sample for detecting scattered light and fluorescence efficiently.
4.3 Sample unit
4.3.1 Cell
The area of a sample shall be substantially larger than the area irradiated by the excitation light, and
the thickness of a sample in the incident plane shall be at least 2 mm.
A sample cell shall be made of a chemically and physically stable material which does not contaminate
the sample inside and can be used in conjunction with a cell holder. A rectangular cell, a flat plate cell
and a Petri dish can be used as a sample cell.
For normal incidence geometry (geometry A described in 4.1, for example), the surface of the powder
sample shall be exposed directly by the excitation light: i.e., it shall not be covered with any other
materials to prevent specular or diffuse reflection.
For geometries other than normal incidence (geometry B described in 4.1, for example), the surface of
powder sample may be covered by a transparent plate or lid with sufficient optical transmittance over
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ISO 13915:2023(E)
the entire measured wavelength range. The thickness and type of material of such plate or lid shall be
identical for the measurement of phosphor materials under test and that of reference materials.
When using a rectangular cell, the incident side of the cell shall be transparent and have sufficient
optical transmittance over the entire measured wavelength range. The rectangular cell can be placed
on the cell holder so that the incident side be vertical. It may also be placed so that the incident side be
horizontal only when the cell is well sealed.
When using a flat plate cell or a Petri dish, the top surface of the cell shall have a cover glass or a lid to
prevent the sample powder from dispersing and contaminating its surroundings during transport or
preparation for installation.
4.3.2 Sample compartment and cell holder
A sample cell can be placed inside the sample compartment. The inner surface of the compartment as
well as each component incorporated inside the compartment such as a cell holder should have a matte
black surface to reduce stray light. The stray light can further be reduced by appropriately placing
apertures in the compartment or by giving the sample cell a slight tilt angle to block the specular
reflection on the surface of the cell from entering the detector.
4.4 Detection unit
4.4.1 Directing optical system
Fluorescence light and scattered light from the sample surface is directed through a directing optical
system to a spectrometer. The directing optical system shall have sufficient transmissivity over the
entire measured spectral range. A focusing optics or an optical fibre probe can be used as a directing
optical system.
4.4.2 Spectrometer and detector
This equipment converts light directed through the directing optical system to electrical signals
proportional to the intensity spectrum of the light. A photomultiplier or a CCD detector, with sufficient
sensitivity over the measured spectral range, is an example of a detector. A scanning monochromator is
a typical example, but an array spectrometer can also be used.
4.4.3 Amplifier
This device amplifies the electrical signal from the detector for data processing.
4.5 Signal and data processing unit
This unit separates and processes signals required for measurement, outputs light intensity for each
measured wavelength as a photon number or energy and saves the associated data.
5 Calibration, inspection and maintenance of measurement apparatus
5.1 General
Measuring equipment should be calibrated in the proper manner for accurate optical measurement.
In addition, the equipment as well as its accessories should be maintained to keep it in an optimal
condition. The quality control manager should make sure that a regular checking procedure is
undertaken according to the manufacturer’s suggestions. Routine factory checking by the manufacturer
is also desirable.
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ISO 13915:2023(E)
5.2 Wavelength calibration of light source unit
When using a monochromated light source, use a monochromator whose wavelength is calibrated with
the line source (e.g., a low-pressure mercury, argon or neon lamp) of known wavelength. A phosphor
material, where some of the peak wavelengths of the line-shaped fluorescence spectrum are measured
by the spectrometer whose wavelength is properly calibrated, can be used as a secondary light source
for wavelength calibration (see Annex A). When using a laser light source, verify the wavelength emitted
using a spectrometer or wavemeter calibrated separately for wavelength.
5.3 Cells
Handle cells carefully to avoid damage. Replace damaged cells with new items.
5.4 Wavelength calibration of detection unit
Use a spectrometer whose wavelength is calibrated with the line source (e.g., a low-pressure mercury
lamp) of known wavelength. A phosphor material where some of the peak wavelengths of the line-
shaped fluorescence spectrum are measured by the spectrometer whose wavelength is properly
calibrated can be used as a secondary light source for wavelength calibration (see Annex A).
5.5 Spectral responsivity calibration
The relative spectral responsivity of the detecting unit should be properly calibrated in accordance
with the manufacturer’s instructions. All measurement spectra should be corrected based on the
relative spectral responsivity calibration results.
NOTE Even if the fluorescence spectra of the reference material and phosphor material under test do not
match well, accurate spectral responsivity calibration can effectively reduce the measurement uncertainty.
6 Samples
6.1 Reference material
A phosphor material whose external quantum efficiency, internal quantum efficiency and absorptance
have been measured in accordance with ISO 23946 shall be used as a reference material for substitution
measurement. These optical properties of the reference material should be measured with conditions
as close as possible in terms of excitation wavelength and angle of incidence to those for the substitution
measurement of the phosphor material under test to the reference material.
The reference material applied to obtain external quantum efficiency of the phosphor material
under test from spectral component of fluorescence may be different from that applied to obtain the
absorptance from the spectral component of scattered light (see 8.3).
NOTE 1 Selection of a reference material whose absorptance value is similar to that of a phosphor material
under test can reduce measurement uncertainty of its absorptance and internal quantum efficiency.
NOTE 2 Selection of a reference material whose fluorescence spectrum is similar to that of a phosphor material
under test can reduce measurement uncertainty of its external quantum efficiency. Chromaticity coordinates
(see Annex B) and dominant wavelength are typical values indicating spectral similarity.
6.2 Storage and pre-processing
Phosphor samples shall be stored appropriately according to their properties and pre-processed as
necessary. Samples can normally be stored at ambient temperature in a desiccator; however, samples
which react with airborne moisture and samples which can be degraded by UV or visible light should be
stored with an inert gas under seal using a glove box or a coloured bottle.
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ISO 13915:2023(E)
Samples which absorb moisture readily should be dried before measurement in a vacuum dry oven at a
non-deteriorating temperature.
6.3 Filling cells with phosphor powders
When using a rectangular cell, place the powder sample in the cell and tap it to ensure th
...