Joint evaluation of three exemptions for cadmium quantum dots applications in display and lighting

• Author: Clemm, Christan; Löw, Clara; Baron, Yifaat; Moch, Katja; Möller, Martin; Köhler, Andreas R; Gensch, Carl-Otto; Deubzer, Otmar
• Pages: 15-52

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phthalate (DEHP), butyl benzyl phthalate (BBP), dibutyl phthalate (DBP), diisobutyl

phthalate (DiBP).7

Compiled information in this re spect has been included, with short clarifications where

relevant, in Tables 1 and 2, which appear in Appendix 1.

The information has further been cross-checked in relation to the exemption evaluated

in the course of this project. This has been done to clarify that the Article 5(1)(a)

threshold-criteria quoted above is complied with in cases where an exemption is to be

granted / its duration renewed / its formulation amended / or where it is to be revoked

and subsequently to expire as an exemption. The considerations in this regard are

addressed in the separate ch apter in which the exemption evaluation is documented

(Chapter 4) under the relevant section titled “REACH compliance – Relation to the

REACH Regulation” (Section 4.4.1).

4. Joint evaluation of three exemptions for cadmium

quantum dots applications in display and lighting

Declaration

In the sections that precede the “Critical review” the phrasings and wordings of

applicant’s and stakeholders’ explanations and arguments have been adopted from the

documents provided by the stakeholders as far as required and reasonable in the context

of the evaluation at hand. Formulations were only altered or completed in cases where

it was necessary to maintain the readability and comprehensibility of the text. These

sections are based exclusively on information provided by applicants and stakeholders,

unless otherwise stated.

Acronyms and definitions

BLU Back light unit

CCT Correlated Color Temperature

Cd Cadmium

CdS Cadmium sulfide

CdSe Cadmium Selenide

CRI Color Rendering Index

FWHM Full width half maximum

InP Indium phosphide

LCA Life cycle assessment

7 The four phthalates, DEHP, BBP, DBP and DIBP have been added to the Annex according to Commission

Delegated Directive (EU) 2015/863 of 31 March 2015.

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LE LightingEurope

Najing Najing technology Co. Ltd

OSRAM OSRAM Opto Semiconductor GmbH

PFS Potassium fluorosilicate

QD Quantum dots

SSL Solid state lighting

4.1. Background

LightingEurope (2017) explains that quantum dots (QDs) are a relatively new material

class that, like phosphors, down convert light from higher energy wavelengths of

typically blue light to lower energy wavelengths in the visible and near-infra-red range.

Key characteristics of quantum dots are explained to be their potentially very high

efficiency, their narrow emission spectrum, and that their emission wavelength can be

accurately tuned across the entire visible spectrum. The narrow emission spectrum

prevents the needless generation of invisible infrared radiation. No other downconverter

exists which exhibits narrow emission (<40 nm full width at half maximum, or FWHM),

is wavelength-tunable to within 1 nm, and has very high photoluminescence quantum

efficiencies, both at room temperature and LED operating temperatures. Considering

these features, QDs can be used to improve the performance and energy efficiency of

today’s white phosphor-converted LEDs by replacing one or more of the phosphors used

as light down converting elements.

Quantum dots (QDs) are to have sizes ranging from 1~100 nm, that have a quantum

confinement effect. By tuning the sizes of the crystals through their synthesis process,

QDs can be produced to emit different wavelengths. Such wavelengths can cover the

whole visible light spectrum from blue wavelength range to red wavelength range. The

possibility to tune the light emitting properties of QDs is explained to differentiate them

from other photo-luminescent materials, such as phosphor, or organ ic dye. (Najing

2018)

According to the information provided by the applicants (LightingEurope 2017; Najing

2018; OSRAM 2018), QDs are used among others in display applications and in lighting

applications (solid state lighting or SSL). LightingEurope (2017) explains that cadmium

is a component in II-IV semiconductor quantum dots (typically based on CdSe or CdS)

and is used in the quantum dot core or quantum dot shell.

Besides their colour emission properties, Cd QDs show higher energy efficiency as

compared with other traditional components used in displays, such as phosphor LED or

cold cathode fluorescent lamps. Through their development, cadmium-based QDs now

achieve around 20~30 nm of FWHM and are stable in display applications, with expected

lifetime for 10 years. (Najing 2018)

As for use in solid state lighting, LightingEurope (2017) further explains that the use of

Cd-containing quantum dots in on-chip LED applications will enhance the luminous

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efficacy8 of LEDs by 10-20 % (based on Correlated Color Temperature (CCT) and Color

Rendering Index (CRI)) above best-available conventional phosphors. This provides

significant energy savings said to outweigh the potentially negative effects of the

amount of cadmium entering the market through this application.

Najing technology Co. Ltd (hereinafter Najing) requests (Najing 2018) a renewal of

exemption 39a of Annex III of RoHS for a period of two years. The exemption is

requested with the following formulation:

“Cadmium selenide in downshifting cadmium-based semiconductor nanocrystal

quantum dots for use in display lighting applications (<0.1 g per mm2 of display

screen area)”

Najing (2018) requests the exemption for quantum dot light converting film used in

display devices and specifically addresses category 1 (Large household appliances);

category 2 (small household appliances); category 4 (consumer equipment) and

category 5 (lighting equipment) in its request. Though its application provides detail

only for on-surface applications, Najing contends that the scope of the exemption should

not be limited to on-surface applications, but should remain available to all application

configurations. Najing (2019) later specified that it requests the exemption be renewed

until 31 October 2021.

Najing (2018) explains that the use of Cd QD in various application areas allows

producing devices (e.g., lighting applications, display applications) that provide

improved colour performance (e.g., warmer light output in lighting, higher colour gamut

in displays). Additionally, this improved performance can be achieved alongside higher

energy efficiency of the product in comparison to alternative technologies (examples

are given to show the benefit in terms of energy consumption). In this respect the

applicants’ main justification for the exemption request refers to the potential for

savings in energy consumption in relation to similar EEE.

OSRAM GmbH and OSRAM Opto Semiconductor GmbH (hereafter OSRAM) also request

to renew the exemption for 5 years, but propose the following wording for this purpose

(OSRAM 2018):

“Cadmium in downshifting semiconductor nanocrystal quantum dots directly

deposited on LED chips for use in display and projection applications (< 5g Cd

per mm² of light emitting LED chip surface)”

OSRAM (2018) explains that the change of wording is mainly related to the shift from

surface and edge illumination to on-chip technology. The on-chip technology is

explained to be innovative and to require additional research for the development of the

LED itself as well as existing and new applications.

8 According to LightingEurop e (201 8), “luminous efficacy is a measure of how efficiently a light so urce

produces visible light. It is the ratio of luminous flux to input electrical power, measured in lumens per

watt of energy used.”