TECHNOLOGIES & APPLICATIONS

UV and VUV excilamps

What is excilamp?

Definition
Excimer and exciplex molecules
Comparison of radiation spectra of excilamps with spectra of conventional sources of radiation
Excitation methods of excimer and exciplex luminescence

1. Definition

Excilamps are sources of spontaneous radiation in UV and VUV spectral ranges, being emissive due to decay of excimer molecules (from excited dimer (excimer) if we say about a molecule consisting of equal atoms, for example Xe₂*) or exciplex molecules (from excited complex (exciplex) if we say about a herteronuclear molecule, for example XeCl*).

Example 1. General view of an KrCl-excilamp of barrier discharge with radiant power of 50 W tested at LOR (Institute of High Current Electronics SB RAS, 2002)

2. Excimer and exciplex molecules

Depending on gas type and conditions, in which an electric discharge is realized, exciplex/excimers may form due to different mechanisms, and the typical radiation lifetime of excited molecules is 10^-7-10^-9 s. Spontaneous decay of excimer and exciplex molecules to single atoms is accompanied by decay lag of a light quantum typical for this molecule

Example 2. The waveforms of radiation as function of wavelength for various excimers and exciplexes (adapted by Оbara M. Recent progress of excimer radiation - research, development and application // Proc. of the 7th Intern. Symposium on the Science and Technology of Light Sources. Kyoto-Japan, 1995. P.149 - 159).

3. Comparison of radiation spectra of excilamps with spectra of conventional sources of radiation

Most conventional UV lamps emit no more than 15 % energy in the range of wavelengths shorter than 300 nm, and with rare exception that is emitted non-selectively (in a wide range of wavelengths).

Example 3. Spectral distribution of radiation intensity for conventional sources of radiation: a flashlamp Purus Pulsed Xe (1), average pressure mercury tube Heraeus Ink Curing Lamp (2), and average pressure mercury tube Hanovia Med. Press. Hg (3) (on Haag W.R. Comparison of commercial lamps for radical oxidation and direct photolysis in water // Preprint of Lawrence Livermore National Laboratory. 1996. 6 August).

Most excilamps have major part of radiant flux concentrated in UV- or VUV-range, in a comparatively narrow spectral zone with half-width from 2 to 15 nm (subject to working molecule):

Example 4. The typical spectra of radiation of some excimer (above) and exciplex (below) molecules.

Wavelengths for exciplex molecules main transitions
R - atom of inert gas	Y - atom of a halogen	The main wavelengths of YT* molecule on various transitions, nm
R - atom of inert gas	Y - atom of a halogen	D_1/2→X_1/2	B_1/2→X_1/2	C_1/2→A_1/2	D_1/2→A_1/2
Ne	F	106	108	110	111
Ar	F	185	193	203	204
Ar	Cl		175		195
Ar	Br		165	172	183
Kr	F	220	248	275	272
Kr	Cl	200	222	240	235
Kr	Br		207	222	228
Kr	I		190	195	225
Xe	F	264	351	460	410
Xe	Cl	236	308	345	340
Xe	Br	221	282	300	325
Xe	I	203	253	265	320

Wavelengths for transitions of excimer molecules and homonuclear molecules of halogenides
R₂*	Wavelength, nm
Ar₂*	126
Kr₂*	146
Xe₂*	172
F₂*	158
Cl₂*	258
Br₂*	291
I₂*	342

4. Excitation methods of excimer and exciplex luminescence

Selection for a working mixture and optimal conditions of excilamps excitation allow obtaining the highest power and efficiency values of radiation at the wavelengths close to maximum band of the working molecule. However, acquisition of such powerful and efficient UV at continua of a number of excimers is restricted by the properties of gas mixtures and systems used for excitation to be realized.
Theoretically:

a discharge in an excilamp should be volumetrically uniform;
a system and excitation method should provide energy deposition in a gas discharge under optimal mixtures, and pressure, density and temperature values of electrons;
a radiator should be effectively cooled at high excitation powers both in continuous or pulse-repetitive modes;
working mixture degradation in a discharge should be minimal, in order the light source have long lifetime (from tens to thousands hours, depending on specified application).

It is impossible to satisfy these conditions in practice due to excitation of working gas mixtures in excilamps by specified discharge type has its own specific character.

To date most attractive commercially are excilamps excited by a barrier or a capacitive discharges:

Example 5. Various methods to obtain exciplex and excimer luminescence.

Laboratory of optical radiation is much experienced in investigation, development and application of excilamps. Should you take an interest in our developments, do not hesitate connecting our specialists.

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