prEN 16981

Photocatalysis - Glossary of terms

A common language for standards, disclosed to a wide audience and referring only to the operational protocols and to their outcomes, is needed both for a consistent set of standards and the connection with the scientific literature. This glossary will take into account existing glossary of terms used in photocatalysis and photochemistry. Because in photocatalysis numerous properties are difficult to be evaluated, it is strongly recommended in standard norms to avoid reporting properties depending on number of actives sites, the mechanisms of adsorption or kinetic mechanisms of photocatalytic reactions. For the same reason instead of the quantum yield and related quantities it is easier to report the photonic efficiency.
Most of the definitions reported in this document are a sub-set of the IUPAC definitions in photocatalysis and radiocatalysis [1]. Some other definitions, in particular for the photocatalytic rate and reactors are taken from a dedicated work [2]. The use and many technical specifications on the physical values suggested for irradiation conditions in the standards are reported in a separate Technical Specification [3].
The arrangement of entries is alphabetical, and the criterion adopted by the IUPAC has been followed for the typeface used: italicized words in a definition or following it indicate a cross-reference in the Glossary.

Photokatalyse - Glossar der Begriffe

Eine einheitliche Sprache wird für Normen, die für ein breites Publikum veröffentlicht werden und sich nur auf die Verfahrensprotokolle und deren Ergebnisse beziehen, sowohl für ein konsistentes Normenwerk als auch für die Verbindung zur wissenschaftlichen Literatur benötigt. Dieses Glossar wird bestehende Verzeichnisse von in der Photokatalyse und Photochemie verwendeten Begriffen berücksichtigen. Da in der Photokatalyse zahlreiche Eigenschaften zahlenmäßig schwer zu bestimmen sind, wird dringend empfohlen, in Standardanforderungen die Angabe von Eigenschaften, die von der Anzahl der aktiven Stellen, den Absorptionsmechanismen oder kinetischen Mechanismen der photokatalytischen Reaktionen abhängig sind, zu vermeiden. Aus dem gleichen Grund ist es leichter, statt der Quantenausbeute und verwandter Größen die photonische Leistung anzugeben.
Die meisten in diesem Dokument aufgeführten Definitionen sind eine Teilmenge der IUPAC-Definitionen in der Photokatalyse und Radiokatalyse [1]. Einige andere Definitionen, insbesondere für die photokatalytische Reaktionsgeschwindigkeit und Reaktoren, sind einer zugeordneten Veröffentlichung entnommen [2]. Die Anwendung und viele Technische Spezifikationen zu den physikalischen Werten, die für Einstrahlungs-bedingungen in den Normen vorgeschlagen wurden, sind in einer separaten Technischen Spezifikation wiedergegeben [3].
Die Einträge sind alphabetischN1 angeordnet und die von der IUPAC übernommenen Kriterien wurden für das Schriftbild befolgt: kursiv geschriebene Worte in oder nach einer Definition weisen auf einen Querverweis im Glossar hin.
N1   Nationale Fußnote: Die alphabetische Sortierung bezieht sich auf die englische Referenzfassung.

Photocatalyse - Glossaire de termes

Un langage commun, couvrant une large audience et faisant référence uniquement aux protocoles opérationnels et à leurs résultats, est nécessaire pour disposer d’un ensemble de normes cohérentes en lien avec la littérature scientifique. Le présent glossaire prend en compte le glossaire de termes existant utilisé en photocatalyse et photochimie. Parce que les nombreuses propriétés de la photocatalyse sont difficiles à évaluer, il est fortement recommandé que les normes relatives à la photocatalyse évitent de consigner des propriétés dépendant du nombre de sites actifs, des mécanismes d’adsorption ou des mécanismes cinétiques des réactions photocatalytiques. Pour les mêmes raisons, à la place du rendement quantique et des quantités associées, il est conseillé d’utiliser l’efficacité photonique.
La plupart des définitions consignées dans le présent document correspondent aux définitions de l’Union internationale de chimie pure et appliquée (UICPA) en photocatalyse et radiocatalyse [1]. D’autres définitions, en particulier celles relatives à la vitesse photocatalytique et aux réacteurs, sont tirées d’un travail dédié [2]. Certaines valeurs physiques relatives aux conditions d’irradiation ainsi que des informations sur leur utilisation sont précisées dans une Spécification technique distincte [3].
L’ordre des entrées est alphabétique et le critère adopté par l’UICPA a été suivi pour les types de caractères utilisés : les mots en italique dans ou à la suite d’une définition indiquent une référence croisée dans le Glossaire.

Fotokataliza - Slovar izrazov

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN 16981:2020
01-junij-2020
Fotokataliza - Slovar izrazov
Photocatalysis - Glossary of terms
Photokatalyse - Glossar der Begriffe
Photocatalyse - Glossaire de termes
Ta slovenski standard je istoveten z: prEN 16981
ICS:
01.040.25 Izdelavna tehnika (Slovarji) Manufacturing engineering
(Vocabularies)
25.220.01 Površinska obdelava in Surface treatment and
prevleke na splošno coating in general
oSIST prEN 16981:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 16981:2020
DRAFT
EUROPEAN STANDARD
prEN 16981
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2020
ICS 01.040.25; 25.220.01 Will supersede CEN/TS 16981:2016
English Version
Photocatalysis - Glossary of terms
Photocatalyse - Glossaire de termes Photokatalyse - Glossar der Begriffe

This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee

CEN/TC 386.

If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations

which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC

Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are

aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without

notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 16981:2020 E

worldwide for CEN national Members.
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Contents Page

European foreword ....................................................................................................................................................... 3

Introduction .................................................................................................................................................................... 4

1 Scope .................................................................................................................................................................... 5

2 Generalities ....................................................................................................................................................... 5

2.1 Note on units ..................................................................................................................................................... 5

2.2 Note on symbols ............................................................................................................................................... 5

2.3 Note on the relationship between spectral, radiometric, and photonic quantities ................ 5

3 Terms and definitions ................................................................................................................................... 6

Bibliography ................................................................................................................................................................. 47

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European foreword

This document (prEN 16981:2020) has been prepared by Technical Committee CEN/TC 386

“Photocatalysis”, the secretariat of which is held by AFNOR.
This document is currently submitted to the CEN Enquiry.
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Introduction

Photocatalysis is a very efficient advanced oxidation technique which enables the production of active

species following light absorption by the photocatalyst, such as bound/free hydroxyl radicals (∙OH),

hydroperoxyl radicals (∙OOH), conduction band electrons and valence band holes, capable of partly or

completely mineralising/oxidising the majority of organic compounds. The most commonly used

photocatalyst is titanium dioxide (TiO ), because it is thermodynamically stable, non-toxic and

economical. Photocatalysts can be used in powder form or deposited as thin film on different substrates

(glass fibre, fabrics, plates/sheets, etc.). The objective of standardization is to introduce test standards

for evaluation of the performance of photocatalysts (including photocatalysis and photo-induced effects).

These standards mainly concern tests and analysis methods, and require a common language.

Safety statement

Persons using this document should be familiar with the normal laboratory practice, if applicable. This

document does not address safety problems, if any, associated with its use. It is the responsibility of the

user to establish appropriate safety and health practices and to ensure compliance with any regulatory

conditions.
Environmental statement

It is understood that some of the material described in this document may have negative environmental

impact. As technological advantages lead to better alternatives for these materials, they will be eliminated

from this document to the possible extent.

At the end of the test, the user of this document will take care to carry out an appropriate disposal of the

wastes, according to local regulation.
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1 Scope

A common language for standards, disclosed to a wide audience and referring only to the operational

protocols and to their outcomes, is needed both for a consistent set of standards and the connection with

the scientific literature. This glossary will take into account existing glossary of terms used in

photocatalysis and photochemistry. Because in photocatalysis numerous properties are difficult to be

evaluated, it is strongly recommended in standard norms to avoid reporting properties depending on

number of actives sites, the mechanisms of adsorption or kinetic mechanisms of photocatalytic reactions.

For the same reason instead of the quantum yield and related quantities it is easier to report the photonic

efficiency.

Most of the definitions reported in this document are a sub-set of the IUPAC definitions in photocatalysis

and radiocatalysis [1]. Some other definitions, in particular for the photocatalytic rate and reactors are

taken from a dedicated work [2]. The use and many technical specifications on the physical values

suggested for irradiation conditions in the standards are reported in a separate Technical Specification

[3].

The arrangement of entries is alphabetical, and the criterion adopted by the IUPAC has been followed for

the typeface used: italicized words in a definition or following it indicate a cross-reference in the Glossary.

2 Generalities
2.1 Note on units

SI units are adopted, with some exceptions, prominently in the use of the molar decadic absorption

3 –1 –1

coefficient, ε, with common units dm mol cm and a mole of photons denoted as an einstein. As recently

the definition of the SI units was established in terms of a set of seven defining constants, including the

Avogadro number, the mole (symbol: mol) is the base unit of amount (number) of substance.

2.2 Note on symbols

Functional dependence of a physical quantity f on a variable x is indicated by placing the variable in

parentheses following the symbol for the function; e.g. ε(λ). Differentiation of a physical quantity f with

respect to a variable x is indicated by a subscript x; e.g. the typical spectral radiant power quantity P =

dP/dλ. The natural logarithm is indicated with ln, and the logarithm to base 10 with log.

For the magnitudes implying energy or photons incident on a surface from all directions, the set of

symbols recommended by the International Organization for Standardization (ISO) [4] and included in

the IUPAC “Green Book”, and by the International Commission on Illumination [5] are adopted, i.e. H or

F for fluence, E for fluence rate, H or F for photon fluence, and E for photon fluence rate, note the

o o p,o p,o p,o

letter o as subscript. This has been done primarily to comply with internationally agreed-upon symbols.

It is important, however, to avoid confusion with the terms used to designate an amount of energy (or

photons) prior to absorption. In these cases, the superscript 0 (zero) is used.

2.3 Note on the relationship between spectral, radiometric, and photonic quantities

When a quantity expressed in photonic units (G ) covers a wavelength range (polychromatic irradiation

between λ and λ ), then G is the integral between λ and λ of the corresponding spectral photonic

1 2 p 1 2
quantity, G (λ):
λ 2
G = G (λ) dλ (e.g., spectral photon flux)
p p
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Since a spectral radiometric or energetic quantity at a given wavelength λ (G , e.g. spectral radiant power,

e,λ

P nm , is related to the corresponding photonic quantity at the same wavelength (G , e.g. spectral

λ/W p,λ
−1 −1
photon flux / s nm ) by the relation:
G = E(λ) G
e,λ p,λ
with
E(λ) = h c/λ, the energy of a photon of wavelength λ.

The relation between photonic (G ) and corresponding radiometric (or energetic, G ) quantity is given

p e
by:
λ 2
G = h c G (λ) 1/λ dλ
e p
or, more useful in practice:
λ 2
G = (1/h c) G (λ)λ dλ
p e

Therefore, for example, to calculate a photon flux over a wavelength interval, the spectral distribution of

the radiant power is necessary. Note that in the Glossary no sub-index e has been used for the radiometric

quantities. Radiometric quantities (G , as above, radiant power and others) are needed because lamp

providers usually give the spectral distribution of the lamps in these units, and not in photonic units (G ,

photon flux and other photonic quantities) and because of quantification of radiation using, e.g.

radiometers.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
absorbance, Ae

logarithm to the base 10 (linear absorbance) of the incident (prior to absorption) spectral radiant power,

P divided by the transmitted spectral radiant power, P :
 
 
A λλ= log =−logT
( ) ( )
 
 

Note 1 to entry: T(λ) is the (internal) transmittance at the defined wavelength. The terms absorbancy, extinction,

and optical density should not be used. When natural logarithms are used, the napierian absorbance is the logarithm

P divided by the transmitted spectral radiant power, P :
to the base e of the incident spectral radiant power, λ
 0
 
A λλ= ln =−lnT
( ) ( )
 
 

Note 2 to entry: These definitions suppose that all the incident ultraviolet, visible, or infrared radiation is either

transmitted or absorbed, reflection or scattering being negligible. Attenuance should be used when this supposition

cannot be made.
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Note 3 to entry: In practice, A is the logarithm to the base 10 of the spectral radiant power of ultraviolet, visible,

or infrared radiation transmitted through a reference sample divided by that transmitted through the investigated

sample, both observed in identical cells.

Note 4 to entry: In common usage, A is given for a path length of 1 cm, unless otherwise specified.

Note 5 to entry: Traditionally, (spectral) radiant intensity, I , was used instead of spectral radiant power, P , now

λ λ
the accepted term.

Note 6 to entry: The wavelength symbol as a subscript for P and in parenthesis for T and A may be omitted.

However, the wavelength should be specified for which the value of the particular property is reported.

Note 7 to entry: Same as internal optical density, which is a term not recommended.

Note 8 to entry: See also absorption coefficient, absorptance, attenuance, Beer–Lambert law, Lambert law, molar

absorption coefficient.
3.2
absorbed (spectral) photon flux density

number of photons of a particular wavelength, per time interval (spectral photon flux, number basis, q ,

p,λ
or spectral photon flux, amount basis, q ) absorbed by a system per volume, V
n,p,λ
−1 –4 –1 –3 –1

Note 1 to entry: On number basis, SI unit is s m ; common unit is s cm nm . On amount basis, SI unit is mol

–1 –4 −1 −3 –1
m ; common unit is einstein s cm nm .
− Aλ − Aλ
( ) ( )
0 0
q 1− 10 q 1− 10
 
p,λ n,p,λ
 
Note 2 to entry: Mathematical expression: on number basis, on amount
V V

basis, where A(λ) is the absorbance at wavelength λ and superscript 0 (zero) indicates incident photons.

Note 3 to entry: Absorbed (spectral) photon flux density (number basis or amount basis) is used in the

denominator when calculating a differential quantum yield and using in the numerator the rate of change of the

number, dC/dt, or the rate of change of the amount concentration, dc/dt, respectively.

3.3
absorbed (spectral) radiant power density

spectral radiant energy per time interval (spectral radiant power, P ) absorbed by a system per volume, V

–4 –3 –1
Note 1 to entry: SI unit is W m ; common unit is W cm nm .
− Aλ
( )
P 1-10

Note 2 to entry: Mathematical expression: where A(λ) is the absorbance at wavelength λ and

superscript 0 (zero) indicates incident radiant power.
3.4
absorptance, a

fraction of ultraviolet, visible, or infrared radiation absorbed, equal to one minus the transmittance (T),

i.e., (1 - T)

Note 1 to entry: The use of this obsolete term, equivalent to absorption factor, is not recommended.

Note 2 to entry: See also absorbance.
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3.5
absorption (of electromagnetic radiation)

transfer of energy from an electromagnetic field to a material or a molecular entity

Note 1 to entry: In a semiclassical fashion, this transfer of energy can be described as being due to an interaction

of the electric field of the wave with an oscillating electric dipole moment set up in the material or molecular entity.

This dipole moment is the result of the perturbation by the outside field, and its oscillation frequency ν is given by

the difference ΔE of the energies of the lower and upper state in the absorbing material or molecular entity, ΔE = hν.

When the frequency of the oscillating dipole moment and the frequency of the field agree, a resonance occurs and

energy can flow from the field into the material or molecule (an absorption occurs).

Note 2 to entry: When energy flows from the material or molecule to the field, stimulated light emission occurs.

Note 3 to entry: The oscillating electric dipole moment produced in the material or molecular entity has an

amplitude and direction determined by a vector Mif, known as the electric transition (dipole) moment. The

amplitude of this moment is the transition moment between the initial (i) and final states (f).

3.6
absorption coefficient (linear decadic a or linear napierian α)
absorbance, A(λ), divided by the optical pathlength, l:
 
A()λ 
 
a(λ) log
 
ll P
 
where

P and P are, respectively, the incident and transmitted spectral radiant power. When napierian

logarithms are used
 
 
αλ( ) a(λ)ln 10 ln
 
 
where
α is the linear napierian absorption coefficient

Note 1 to entry: Since absorbance is a dimensionless quantity, the coherent SI unit for a and α is m ; the common

unit is cm .
Note 2 to entry: See also absorptivity, molar absorption coefficient.
3.7
absorption cross-section, σ

linear napierian absorption coefficient, α(λ), divided by the number of molecular entities contained in a

volume of the absorbing medium along the ultraviolet, visible, or infrared radiation path:

 0
a()λ
 
σλ( ) ln
 
C Cl P
 
where
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C is the number concentration of molecular entities (number per volume), l is the optical pathlength,

and P and P are, respectively, the incident and transmitted spectral radiant power

2 2
Note 1 to entry: SI unit is m , common unit is cm .

Note 2 to entry: The relation between the absorption cross-section and the molar (decadic) absorption coefficient,

ε(λ), is α(λ) = ln10 ε(λ)/NA with NA the Avogadro constant. A conversion equation in common units is:

2 −21 –1 3 –1
σ(λ)/cm = (3.8236 × 10 /mol) × [ε(λ)/ mol dm cm ]
Note 3 to entry: See also attenuance, Beer–Lambert law.
3.8
absorption factor
fraction of ultraviolet, visible, or infrared radiation absorbed by a system
–A(λ)
f(λ) = 1 – T(λ) = 1 – 10
with
T(λ) the transmittance and A(λ) the absorbance at a particular wavelength λ
Note 1 to entry: This term is preferred to absorptance.

Note 2 to entry: The wavelength symbol may be omitted for f, T, and A. The wavelength should be specified for

which the value of the particular property is reported.
Note 3 to entry: For A(λ) << 1/ln10, f(λ) approximately A(λ) ln10.
3.9
absorption spectrum

plot of the absorbance or of the absorption coefficient against a quantity related to photon energy, such as

frequency ν, wavenumber ν , or wavelength λ
3.10
absorptivity
absorptance divided by the optical pathlength
Note 1 to entry: The unit length shall be specified.
Note 2 to entry: The use of this obsolete term is not recommended.

Note 3 to entry: For very low attenuance, i.e. for A(λ) << 1/ln10, it approximates the linear absorption coefficient,

–A(λ)
within the approximation [1 – 10 ] approximately A(λ) ln10.
3.11
actinic

applied or referred to actinism. Relating to, resulting from, or exhibiting chemical changes produced by

radiant energy especially in the visible and ultraviolet parts of the spectrum
3.12
actinism
chemical changes on living and nonliving materials caused by optical radiation
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3.13
actinometer

chemical system for the determination of the number of photons integrally or per time interval absorbed

into the defined space of a chemical reactor

Note 1 to entry: This name is commonly applied to systems used in the ultraviolet and visible wavelength ranges.

Note 2 to entry: For example, solutions of potassium oxalatoferrate(III), K3[Fe(C2O4)3] (among other systems)

can be used as a chemical actinometer. Bolometers, thermopiles, and photodiodes are physical devices giving a

reading of the radiation impinging on them that can be correlated to the number of photons detected as well as to

the number of photons entering the chemical reactor. Detailed information on chemical actinometers and

measuring systems can be found in CEN/TS 16599:2014.
Note 3 to entry: See also spectral sensitivity.
3.14
action spectrum

plot of a relative biological or chemical photoresponse (=Δy) per number of incident (prior to absorption)

photons, vs. wavelength, or energy of radiation, or frequency or wavenumber

Note 1 to entry: This form of presentation is frequently used in the studies of biological or solid-state systems,

where the nature of the absorbing species is unknown.

Note 2 to entry: It is advisable to ensure that the fluence dependence of the photoresponse is the same (e.g. linear)

for all the wavelengths studied.

Note 3 to entry: The action spectrum is sometimes called spectral responsivity or sensitivity spectrum. The precise

action spectrum is a plot of the spectral (photon or quantum) effectiveness. By contrast, a plot of the biological or

chemical change or response per absorbed photon (quantum efficiency) vs. wavelength is the efficiency spectrum.

Note 4 to entry: In cases where the fluence dependence of the photoresponse is not linear (as is often the case in

biological photoresponses), a plot of the photoresponse vs. fluence should be made at several wavelengths and a

standard response should be chosen. A plot of the inverse of the “standard response” level vs. wavelength is then

the action spectrum of the photoresponse.
Note 5 to entry: See also excitation spectrum, efficiency spectrum.
3.15
AM 0 sunlight

solar irradiance in space just above the atmosphere of the earth on a plane perpendicular to the direction

of the sun (air mass, AM, zero)
Note 1 to entry: Also called extraterrestrial irradiance.
Note 2 to entry: See also AM 1 sunlight.
3.16
AM 1 sunlight

solar irradiance at sea level, i.e., traversing the atmosphere, when the direction of the sun is perpendicular

to the surface of the earth
Note 1 to entry: Also called terrestrial global irradiance.
Note 2 to entry: See also AM 0 sunlight.
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3.17
attenuance, D

logarithm to the base 10 of the incident spectral radiant power, P , divided by the transmitted spectral

radiant power, P
 
 
DT(λλ)= log =−log
( )
 
 
where
T(λ) is the transmittance

Note 1 to entry: Attenuance reduces to absorbance if the incident beam is only either transmitted or absorbed,

but not reflected or scattered.
Note 2 to entry: See also Beer–Lambert law, depth of penetration.
3.18
attenuance filter
(better use: neutral-density filter)

Note 1 to entry: Detailed information on filters can be found in CEN/TS 16599:2014

3.19
back electron-transfer

term often used to indicate thermal inversion of excited-state electron transfer restoring the donor and

acceptor in their original oxidation state
Note 1 to entry: Process better designated as electron back-transfer.

Note 2 to entry: In using this term, one should also specify the resulting electronic state of the donor and acceptor.

Note 3 to entry: It is recommended to use this term only for the process restoring the original electronic state of

donor and acceptor.

Note 4 to entry: Should the forward electron transfer lead to charge separation, electron back-transfer will result

in charge recombination.
3.20
bandgap energy, E

energy difference between the bottom of the conduction band and the top of the valence band in a

semiconductor or an insulator
Note 1 to entry: See also Fermi level.
3.21
bandpass filter

optical device that permits the transmission of radiation within a specified wavelength range and does

not permit transmission of radiation at higher or lower wavelengths
Note 1 to entry: It can be an interference or a coloured filter.

Note 2 to entry: See also filter. More detailed info on filters can be found in CEN/TS 16599:2014.

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3.22
bathochromic shift (effect)

shift of a spectral band to lower frequency (longer wavelengths) owing to the influence of substitution or

a change in environment (e.g., solvent)

Note 1 to entry: It is informally referred to as a red shift and is opposite to a hypsochromic shift.

3.23
Beer–Lambert law (or Beer–Lambert–Bouguer law)

the absorbance of a beam of collimated monochromatic radiation in a homogeneous isotropic medium is

proportional to the absorption pathlength, l, and to the concentration, c, or (in the gas phase) to the

pressure of the absorbing species

Note 1 to entry: This law holds only under the limitations of the Lambert law and for absorbing species exhibiting

no concentration or pressure dependent aggregation. The law can be expressed as
 
 
A(λ) log ελ cl
( )
 
 
−−Aλ ε λ cl
( ) ( )
PP 10 P 10
λλ λ

where the proportionality constant, ε(λ), is the molar (decadic) absorption coefficient, and P and P are,

λ λ

respectively, the incident and transmitted spectral radiant power. For l in cm and c in mol dm (M), ε(λ) will result

3 –1 –1 –1 –1 2 –1 3 –1 –1

in dm mol cm (M cm ), a commonly used unit. SI unit of ε(λ) is m mol (10 dm mol cm ).

Note 2 to entry: Spectral radiant power shall be used because the Beer–Lambert law holds only if the spectral

bandwidth of the ultraviolet, visible, or infrared radiation is narrow as compared to spectral linewidths in the

spectrum.

Note 3 to entry: See also absorbance, attenuance, extinction coefficient, Lambert law.

3.24
biphotonic excitation

simultaneous (coherent) absorption of two photons (either same or different wavelength), the energy of

excitation being the sum of the energies of the two photons
Note 1 to entry: Also called two-photon excitation.

Note 2 to entry: This term is sometimes also used for a two-step absorption when the absorption is no longer

simultaneous.
3.25
biphotonic process
resulting from biphotonic excitation
Note 1 to entry: See also multiphoton process.
3.26
bleaching

in photochemistry, this term refers to the loss of absorption or emission intensity

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3.27
blue shift
informal expression for hypsochromic shift
3.28
Brewster angle, θ

when an unpolarized planar electromagnetic wavefront impinges on a flat dielectric surface, there is a

unique angle (θ ), commonly referred to as Brewster angle, at which the reflected waves are all polarized

into a single plane
1/2

Note 1 to entry: Expression for Brewster angle: θ = arctan (n / n ) = arctan (ε / ε ) where n and n are the

B 2 1 2 1 2 1

refractive indices of the receiving surface and the initial medium, respectively, and ε and ε are the relative static

2 1
permittivities (formerly called dielectric constants).

Note 2 to entry: For a randomly polarized beam incident at Brewster angle, the electric fields of the reflected and

refracted waves are perpendicular to each other.

Note 3 to entry: For a wave incident from air on water (n = 1,333), glass (n = 1,515), and diamond (n = 2,417), the

Brewster angles are 53, 57, and 67,5 degrees, respectively.
3.29
charge recombination
reverse of charge separation

Note 1 to entry: In using this term, it is important to specify the resulting electronic state of the donor and

acceptor.
3.30
charge separation

process in which, under a suitable influence (e.g., photoexcitation), electronic charge moves in a way that

increases (or decreases) the difference in local charges between donor and acceptor sites. Term often

used in photocatalysis as the generated species in the bands of the semiconductor are charged (electrons

and holes)
Note 1 to entry: Charge recombination reduces (or increases) the difference.

Note 2 to entry: Electron transfer between neutral species is the most common example of charge separation. The

most important example of charge recombination is electron backtransfer occurring after photoinduced charge

separation.
3.31
charge shift

under a suitable influence (e.g., photoexcitation), electronic charge moves without changing the absolute

value of the difference in local charges between the original donor and acceptor sites

Note 1 to entry: Prominent examples are the electron transfer reversing the charges in a system composed of a

neutral donor and a cationic acceptor or of a neutral acceptor and an anionic donor.

3.32
charge-transfer (CT) transition

electronic transition in which a large fraction of an electronic charge is transferred from one region of a

molecular entity, called the electron donor, to another, called the electron acceptor (intramolecular CT)

or from one molecular entity to another (intermolecular CT)

Note 1 to entry: Transition typical for donor-acceptor complexes or multichromophoric molecular entities.

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oSIST prEN 16981:2020
prEN 16981:2020 (E)
Note 2 to entry: See also charge-transfer absorption.
3.33
chemiluminescence

luminescence arising from generation by a chemical reaction of electronically excited molecular entities

from reactants in their ground electronic states
3.34
chromophore

part of a molecular entity consisting of an atom or moiety in which the electronic transition responsible

for a given spectral band above 200 nm is approximately localized

Note 1 to entry: In practice, this definition is extended to a part of a molecular entity in which an electronic

transition responsible for absorption in the ultraviolet region of the spectrum is approximately localized as well as

to a part of a molecular entity in which a vibrational, rotational, or bending transition responsible for absorption in

the infrared region of the spectrum is approximately localized.
3.35
CIELAB
a Lab color space is a color-oppon
...