CEN/TS 16981:2016

SLOVENSKI STANDARD
01-januar-2017
Fotokataliza - Slovar izrazov
Photocatalysis - Glossary of terms
Photokatalyse - Glossar der Begriffe
Photocatalyse - Glossaire de termes
Ta slovenski standard je istoveten z: CEN/TS 16981:2016
ICS:
01.040.25 Izdelavna tehnika (Slovarji) Manufacturing engineering
(Vocabularies)
25.220.20 Površinska obdelava Surface treatment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN/TS 16981
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
November 2016
TECHNISCHE SPEZIFIKATION
ICS 01.040.25; 25.220.20
English Version
Photocatalysis - Glossary of terms
Photokatalyse - Glossar der Begriffe
This Technical Specification (CEN/TS) was approved by CEN on 15 August 2016 for provisional application.

The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to
submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.

CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS
available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in
parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 16981:2016 E
worldwide for CEN national Members.

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 . 53

European foreword
This document (CEN/TS 16981:2016) has been prepared by Technical Committee CEN/TC 386
“Photocatalyse”, the secretariat of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
According to the CEN/CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
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),
perhydroxyl 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 ), the latter being thermodynamically stable, non-toxic and
economical. It can be used in powder form or deposited on a substrate (glass fibre, fabrics,
plates/sheets, etc.). The objective is to introduce performance standards for photo-induced effects
(including photocatalysis). These standards will mainly concern test and analysis methods.
Safety statement
Persons using this document should be familiar with the normal laboratory practice, if applicable. This
document cannot address all of the 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 permitted in this Technical Specification may have negative
environmental impact. As technological advantages lead to better alternatives for these materials, they
will be eliminated from this Technical Specification to the extent possible.
At the end of the test, the user of the Technical Specification will take care to carry out an appropriate
disposal of the wastes, according to local regulation.
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 Technical Specification 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. Note that
“amount concentration” is the preferred term for what has been known as “molar concentration”, and is
complementary to the terms “mass concentration” and “number concentration”.
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
λ
= 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
o
or F for fluence, E for fluence rate, H or F for photon fluence, and E for photon fluence rate, note
o o p,o p,o p,o
the 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
p
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):
p
λ2
Gp = Gp (λ) dλ (e.g., spectral photon flux).
∫
λ1
Since a spectral radiometric or energetic quantity at a given wavelength λ (G , e.g., spectral radiant
e,λ
−1
power, P nm , is related to the corresponding photonic quantity at the same wavelength (G , e.g.,
λ/W p,λ
−1 −1
spectral 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 (Gp) and corresponding radiometric (or energetic, Ge) quantity is given
by:
λ2
G = h c G (λ) 1/λ dλ
e p
∫
λ1
or, more useful in practice:
λ2
G = (1/h c) G (λ)λ dλ
p e
∫
λ1
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
e
because lamp providers usually give the spectral distribution of the lamps in these units, and not in
, photon flux and other photonic quantities) and because of quantification of radiation
photonic units (Gp
using, e.g., radiometers.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
absorbance, A
e
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 :
λ
λ
 
P
λ
Aλλ= log =−logT
( ) ( )
 
P
λ
 
Note 1 to entry: T(λ) is the (internal) transmittance at the defined wavelength. The terms absorbancy, extinction,
and optical density should no longer be used. When natural logarithms are used, the napierian absorbance is the
logarithm to the base e of the incident spectral radiant power, P divided by the transmitted spectral radiant
λ
power, P :
λ
 
P
λ
ATλ = ln =−ln λ
( ) ( )
e
 
P
λ
 
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.
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
s
−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,
λ
V
–4 –3 –1
Note 1 to entry: SI unit is W m ; common unit is W cm nm .
−Aλ
0 ( )
P 1-10
λ
 
 
Note 2 to entry: Mathematical expression: where A(λ) is the absorbance at wavelength λ and
V
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.
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 M , known as the electric transition (dipole) moment. The
if
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 1 P

λ
a(λ) log 

 
l l P

λ
 
where
P and P are, respectively, the incident and transmitted spectral radiant power. When napierian
λ
λ
logarithms are used
 
P
1
λ
a(λ) a(λ)ln10 ln 

 
lP

λ
 
where
α is the linear napierian absorption coefficient.
–1
Note 1 to entry: Since absorbance is a dimensionless quantity, the coherent SI unit for a and α is m ; the
–1
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:

a()λ 1 P
λ
σ(λ) ln

C Cl P
λ

where
==
==
==
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.
λ
λ
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)/N with N the Avogadro constant. A conversion equation in common units is:
A A
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) ≈ 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
–A(λ)
coefficient, within the approximation [1 – 10 ] ≈ 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
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), K [Fe(C O ) ] (among other systems)
3 2 4 3
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.
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.
3.17
amalgam lamp
see mercury lamp
3.18
attenuance, D
logarithm to the base 10 of the incident spectral radiant power,P , divided by the transmitted spectral
λ
radiant power, P
λ

P
λ
DT(λλ)= log=−log
( )

P
λ

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.
3.19
attenuance filter
(better use: neutral-density filter)
3.20
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.
3.21
bandgap energy, E
g
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.
3.22
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 colored filter.
Note 2 to entry: See also filter.
3.23
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.
3.24
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
 
P
λ
 
A(λ) log ε(λ)cl
 
P
λ
 
or
−−A(λ) ε(λ)cl
PP 10 P 10
λλ λ
where the proportionality constant, ε(λ), is the molar (decadic) absorption coefficient, andP and P are,
λ λ
–3
respectively, the incident and transmitted spectral radiant power. For l in cm and c in mol dm (M), ε( λ) will
3 –1 –1 –1 –1 2 –1 3 –1 –1
result 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.
3.25
bioluminescence
luminescence produced by living systems
Note 1 to entry: See also luminescence.
3.26
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.
==
==
3.27
biphotonic process
resulting from biphotonic excitation
Note 1 to entry: See also multiphoton process.
3.28
bleaching
in photochemistry, this term refers to the loss of absorption or emission intensity
3.29
blue shift
informal expression for hypsochromic shift
3.30
Brewster angle, θ
B
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
B
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.
3.31
charge hopping
electron or hole transport between equivalent sites
3.32
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.
3.33
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
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.
3.34
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.
3.35
charge-transfer (CT) absorption
electronic absorption corresponding to a charge-transfer transition
Note 1 to entry: In some cases, the charge-transfer absorption band(s) may be strongly obscured by the local
absorptions of the donor and acceptor systems.
3.36
charge-transfer (CT) complex
ground-state complex that exhibits charge-transfer absorption
Note 1 to entry: See also charge-transfer transition.
3.37
charge-transfer (CT) state
state related to the ground state by a charge-transfer transition
3.38
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.
Note 2 to entry: See also charge-transfer absorption.
3.39
charge-transfer transition to solvent (CTTS)
electronic transition adequately described by single electron transfer between a solute and the solvent,
different from excitation followed by electron transfer to solvent
Note 1 to entry: See also charge-transfer (CT) transition.
3.40
chemiluminescence
luminescence arising from generation by a chemical reaction of electronically excited molecular entities
from reactants in their ground electronic states
3.41
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.
3.42
CIELAB
a Lab color space is a color-opponent space with dimension L for lightness and a and b for the color-
opponent dimensions, based on nonlinearly compressed CIE XYZ color space coordinates
Note 1 to entry: Lab is now more often used as an informal abbreviation for the CIE 1976 (L*, a*, b*) color space
(or CIELAB).
Note 2 to entry: Unlike the RGB and CMYK color models, Lab color is designed to approximate human vision.
Note 3 to entry: See also RGB.
3.43
circular dichroism (CD)
see dichroism
3.44
color scale
see CIELAB, RGB
3.45
conduction band
vacant or only partially occupied set of many closely spaced electronic levels resulting from an array of
a large number of atoms forming a system in which the electrons can move freely or nearly so
Note 1 to entry: Term usually used to describe the properties of metals and semiconductors.
Note 2 to entry: See also bandgap energy, Fermi level, valence band.
3.46
conversion spectrum
plot of a quantity related to the absorption (absorbance, etc.) multiplied by the quantum yield for the
~
considered process, against a suitable measure of photon energy, such as frequency ν, wavenumber , or
ν
wavelength λ
Note 1 to entry: See also action spectrum, efficiency spectrum, spectral effectiveness.
3.47
conversion (chemical)
symbols are arbitrary, often η or X are used
N −−N c c
η
Nc
where
N is the number of molecules or on a chemical basis the moles and c is the concentration entering in
(subscript o) and flowing out the reactor. In a batch reactor, for a reactant A that is converted according
to a first order rate r = k × c, the conversion η=1−−exp( kt) . Typically the conversion is evaluated under
steady state in CSTR of PFR reactors (see Reactor)
==
3.48
CT
acronym for charge transfer
3.49
current yield
see photocurrent yield
3.50
cut-off filter
optical device that only permits the transmission of radiation of wavelengths longer or shorter than a
specified wavelength
Note 1 to entry: Usually, the term refers to devices that transmit radiation of wavelengths longer than the
specified wavelength.
Note 2 to entry: See also cut-on filter, filter.
3.51
cut-on filter
optical device that only permits the transmission of radiation of wavelengths shorter than a specified
wavelength
Note 1 to entry: Although more rare than the cut-off filters, there are a few cut-on filters on the market.
Note 2 to entry: See also cut-off filter, filter.
3.52
dark reaction
chemical reaction that does not require or depend on the presence of light
Note 1 to entry: Contrasts with a photochemical reaction, which is initiated by light absorption by one or more of
the reactants.
Note 2 to entry: A dark reaction is essentially a thermally activated reaction.
3.53
deactivation (of the catalyst)
reduced efficiency of the catalyst due to many possible reasons like poisoning, change of the surface
texture, chemical migration of species
3.54
decay time
time needed for the concentration of an entity to decrease to 1/e of its initial value when this entity
does not disappear by a first-order process
Note 1 to entry: Same as “apparent lifetime”. The use of the latter term is not recommended.
Note 2 to entry: Should the entity disappear by a first-order process, the term lifetime is preferred.
3.55
depth of penetration (of ultraviolet, visible, or infrared radiation)
inverse of the linear absorption coefficient
Note 1 to entry: SI unit is m; common unit is cm.
Note 2 to entry: When the linear decadic absorption coefficient, a, is used, the depth of penetration (1/a) is the
distance at which the spectral radiant power, P , decreases to one-tenth of its incident value, i.e., to /10. When
λ P
λ
the linear napierian absorption coefficient, α, is used, the depth of penetration (1/α = β in this case) is the distance
at which the spectral radiant power decreases to 1/e of its incident value, i.e., to P /e.
λ
Note 3 to entry: See also absorbance, attenuance.
3.56
dichroic filter
see interference filter
Note 1 to entry: The name dichroic arises from the fact that the filter appears one color under illumination with
transmitted light and another with reflected light.
3.57
dichroic mirror
mirror used to reflect light selectively according to its wavelength
3.58
dichroism
dependence of absorbance of a sample on the type of polarization of the measuring beam
Note 1 to entry: This polarization may be linear, corresponding to linear dichroism (LD) in which the difference
in absorption for two perpendicularly linearly polarized beams is measured, ΔA = A – A , or circular dichroism
l Z Y
(CD) in which the difference in absorption for left minus right circularly polarized beams is measured, ΔA = A –
C L
A .
R
3.59
dielectric constant
obsolete term. Now called “relative (static) permittivity”
3.60
differential quantum yield
see quantum yield
3.61
diode light emitting (LED)
see light-emitting diode
3.62
dose
energy or amount of photons absorbed per volume (or per mass) by an irradiated object during a
particular exposure time
–3 –1 –3 –1
Note 1 to entry: SI units are J m or J g and mol m or mol g , respectively.
–3 –1
Note 2 to entry: Common units are einstein m or einstein g , respectively.
Note 3 to entry: In medicine and in some other research areas (e.g., photopolymerization and water purification
through irradiation) dose is used in the sense of exposure, i.e., the energy or amount of photons per surface area
(or per volume) impinging upon an irradiated object during a particular exposure time. This use is not
recommended. The terms photon exposure and radiant exposure are preferred. See also einstein, UV dose.
3.63
driving force
o
the negative of the standard Gibbs energy change (ΔG ) for a particular reaction, e.g., for energy transfer
o
or electron transfer (Δ G )
ET
3.64
driving force (for electron transfer)
term widely used to indicate the negative of the standard Gibbs energy change for outer-sphere electron
o
transfer (Δ G )
ET
Note 1 to entry: For photoinduced processes, this quantity can often be estimated from independently
determined properties of the donor and acceptor species involved using the equation for the calculation of the
Gibbs energy of photoinduced electron transfer.
3.65
efficiency spectrum
plot of the efficiency of a step (η) against wavelength or photon energy
Note 1 to entry: Compare with spectral effectiveness; see also action spectrum, conversion spectrum.
3.66
einstein
mole of photons
Note 1 to entry: Widely used, although it is not an SI unit.
Note 2 to entry: The energy of one einstein of photons of frequency ν is E = N hν, with h the Planck constant and
A
N the Avogadro constant.
A
3.67
electron back-transfer
thermal inversion of excited-state electron transfer restoring the donor and acceptor in their original
oxidation state
Note 1 to entry: In using this term, one should also specify the resulting electronic state of the donor and
acceptor.
Note 2 to entry: This term is preferred to back electron-transfer.
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.
3.68
electron transfer
transfer of an electron from one molecular entity to another or between two localized sites in the same
entity
Note 1 to entry: See also Marcus equation, outer-sphere electron transfer, inner-sphere electron transfer.
3.69
electron-transfer photosensitization
photochemical process in which a reaction of a non-absorbing substrate is induced by electron transfer
(not energy transfer) to or from an ultraviolet, visible, or infrared radiation-absorbing sensitizer
Note 1 to entry: The overall process shall be such that the sensitizer is recycled. Depending on the action of the
excited sensitizer as electron donor or acceptor the sensitization is called, respectively, reductive or oxidative.
Note 2 to entry: See also photosensitization.
3.70
electronically excited state
state of an atom or molecular entity that has higher electronic energy than the ground state of the same
entity
Note 1 to entry: See also excited state.
3.71
emission (of light)
radiative deactivation of an excited state; transfer of energy from a molecular entity to an
electromagnetic field
Note 1 to entry: Same as luminescence.
Note 2 to entry: See also fluorescence, phosphorescence.
3.72
emission spectrum
plot of the emitted spectral radiant power or of the emitted spectral photon irradiance (spectral photon
~
exitance) against a quantity related to photon energy, such as frequency, ν, wavenumber, ν , or

wavelength, λ
Note 1 to entry: When corrected for wavelength-dependent variations in the equipment response, it is called a
corrected emission spectrum.
3.73
emissivity
see emittance
3.74
emittance, e
radiant exitance emitted by an object relative to that of a black body at the same temperature
Note 1 to entry: It is dimensionless.
Note 2 to entry: Mathematical expression: M/M with M and M the radiant exitance of the object and of a
bb bb
black body, respectively.
3.75
energy transfer
excitation transfer. Process by which a molecular entity is excited (e.g., by absorption of ultraviolet,
visible, or infrared radiation or by a chemical reaction that generates electronically excited molecular
entities from reactants in their ground electronic states) and a phenomenon (a physical or a chemical
process) originates from the excited state of another molecular entity, which has interacted with the
originally absorbing entity
Note 1 to entry: In mechanistic photochemistry, the term has been reserved for the process in which an excited
state (produced by absorption of radiation) of one molecular entity (the donor) is deactivated to a lower-lying
state by transferring energy to a second molecular entity (the acceptor), which is thereby raised to a higher
energy state. The excitation may be electronic, vibrational, rotational, or translational. The donor and acceptor
may be two parts of the same molecular entity, in which case the process is called intramolecular energy transfer.
3.76
excitation spectrum
for a particular luminescence wavelength or wavenumber, a plot of the spectral radiant power or of the
spectral radiant exitance or of the spectral photon exitance against the frequency (or wavenumber or
wavelength) of excitation
Note 1 to entry: When corrected for wavelength-dependent variations in the excitation radiant power, this is
called a corrected excitation spectrum.
Note 2 to entry: Due to the proportionality of the emission intensity with the absorbed radiant power, the
excitation spectrum of a unique species should be identical to its absorption spectrum only at very low absorbances.
Note 3 to entry: See also emission spectrum.
3.77
excitation transfer
see energy transfer
3.78
excited state
state of higher energy than the ground state of a chemical entity
Note 1 to entry: In photochemistry, an electronically excited state is usually meant.
3.79
exciton
free exciton. In some applications, it is useful to consider electronic excitation as a quasi-particle that is
capable of migrating
Note 1 to entry: In organic materials, two models are used: the band or wave model (low temperature, high
crystalline order) and the hopping model (higher temperature, low crystalline order or amorphous state). Energy
transfer in the hopping limit is identical with energy migration. In semiconductors and insulators, a free exciton is
a bound electron-hole (neutral quasi-particle) capable of migrating and transferring its energy to the solid lattice.
A localized exciton is an exciton trapped by a defect, which leads to the electronically excited state of the defect. In
electroluminescent materials, excitons are the emissive entities produced by recombination of bipolarons.
3.80
exposure
term generally applied to the time-integrated radiation incident from all upward directions on a small
sphere divided by the cross-sectional area of that sphere
Note 1 to entry: See also photon exposure, radiant exposure.
3.81
extinction
this term, equivalent to absorbance, is no longer recommended
3.82
extinction coefficient
this term, equivalent to molar (decadic) absorption coefficient, is no longer recommended
Note 1 to entry: See also Beer-Lambert law.
3.83
Fermi level, E
F
highest energy level occupied with electrons in the ground state of a solid (metal, semiconductor, or
insulator) or in an electrolyte solution
Note 1 to entry: See also bandgap energy, conduction band, valence band.
3.84
filter (optical)
device that reduces the spectral range (bandpass, cut-off, cut-on, and interference filter) or radiant power
of incident radiation (neutral density or attenuance filter), or both, upon transmission of radiation
3.85
flash photolysis
transient-spectroscopy and transient kinetic technique in which an ultraviolet, visible, or infrared
radiation pulse is used to produce transient species
Note 1 to entry: Commonly, an intense pulse of short duration is used to produce a sufficient co
...