Bendix, J.

Brock-Nannestad, T.

Chorkendorff, Ib

Dethlefsen, J. R.

Vesborg, Peter Christian Kjærgaard

P. C. K. Vesborg

I. Chorkendorff

T. Brock-Nannestad

J. R. Dethlefsen

J. Bendix

Crossref

Review of Scientific Instruments

Note: Simple means for selective removal of the 365 nm line from the Hg spectrum using Dy

Vesborg, P. C. K.

Chorkendorff, I.

Brock-Nannestad, Theis

Dethlefsen, Johannes Rytter

Bendix, Jesper

Copenhagen University Research Information System

The emission spectrum of mercury has a notable line at about 365 nm under both low and medium-high pressure conditions. A simple filter based on a solution of dysprosium ions, Dy3+, is shown to be very useful for applications of Hg-light sources where this line is unwanted. The presented filter is cheap, robust, and stable towards degradation or bleaching - even under intense irradiation. The absorption spectrum for the Dy-filter is presented along with emission spectra from both low-pressure and high-pressure Hg-lamps to illustrate the utility of the technique under best-case and worst-case conditions. Attenuation of the 365 nm spectral line is almost total for the low-pressure source whereas for the high-pressure source the attenuation is about a factor of three. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3639128

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Downloaded from orbit.dtu.dk on: Dec 19, 2017Note: Simple means for selective removal of the 365 nm line from the Hg spectrumusing DyVesborg, Peter Christian Kjærgaard; Chorkendorff, Ib; Brock-Nannestad, T.; Dethlefsen, J. R.; Bendix, J.Published in:Review of Scientific InstrumentsLink to article, DOI:10.1063/1.3639128Publication date:2011Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Vesborg, P. C. K., Chorkendorff, I., Brock-Nannestad, T., Dethlefsen, J. R., & Bendix, J. (2011). Note: Simplemeans for selective removal of the 365 nm line from the Hg spectrum using Dy. Review of Scientific Instruments,82(9), 096102. DOI: 10.1063/1.3639128Note: Simple means for selective removal of the 365 nm line from theHg spectrum using DyP. C. K. Vesborg, I. Chorkendorff, T. Brock-Nannestad, J. R. Dethlefsen, and J. Bendix  Citation: Rev. Sci. Instrum. 82, 096102 (2011); doi: 10.1063/1.3639128 View online: http://dx.doi.org/10.1063/1.3639128 View Table of Contents: http://rsi.aip.org/resource/1/RSINAK/v82/i9 Published by the American Institute of Physics.  Related ArticlesA novel vacuum ultra violet lamp for metastable rare gas experiments Rev. Sci. Instrum. 82, 073106 (2011) Note: Design and characterization of an optical light source based on mixture of white and near-ultraviolet lightemitting diode spectra Rev. Sci. Instrum. 82, 046111 (2011) A novel facility for ageing materials with narrow-band ultraviolet radiation exposure Rev. Sci. Instrum. 82, 023107 (2011) Sharp rise of excitation temperature in the periphery of lamp arcs measured from the 254 nm resonance line ofmercury Appl. Phys. Lett. 97, 221502 (2010) Angular ion emission characteristics of a laser triggered tin vacuum arc as light source for extreme ultravioletlithography J. Appl. Phys. 108, 093304 (2010)  Additional information on Rev. Sci. Instrum.Journal Homepage: http://rsi.aip.org Journal Information: http://rsi.aip.org/about/about_the_journal Top downloads: http://rsi.aip.org/features/most_downloaded Information for Authors: http://rsi.aip.org/authors Downloaded 11 Nov 2011 to 192.38.67.112. Redistribution subject to AIP license or copyright; see http://rsi.aip.org/about/rights_and_permissionsREVIEW OF SCIENTIFIC INSTRUMENTS 82, 096102 (2011)Note: Simple means for selective removal of the 365 nm linefrom the Hg spectrum using DyP. C. K. Vesborg,1,a) I. Chorkendorff,1,b) T. Brock-Nannestad,2,c) J. R. Dethlefsen,2and J. Bendix21Department of Physics, CINF, Technical University of Denmark (DTU), Building 312, Fysikvej,DK-2800 Kgs. Lyngby, Denmark2Department of Chemistry, University of Copenhagen, H. C. Ørsted Instituttet, Universitetsparken 5,DK-2300 København Ø, Denmark(Received 24 February 2011; accepted 23 August 2011; published online 16 September 2011)The emission spectrum of mercury has a notable line at about 365 nm under both low and medium-high pressure conditions. A simple filter based on a solution of dysprosium ions, Dy3+, is shown tobe very useful for applications of Hg-light sources where this line is unwanted. The presented filteris cheap, robust, and stable towards degradation or bleaching – even under intense irradiation. Theabsorption spectrum for the Dy-filter is presented along with emission spectra from both low-pressureand high-pressure Hg-lamps to illustrate the utility of the technique under best-case and worst-caseconditions. Attenuation of the 365 nm spectral line is almost total for the low-pressure source whereasfor the high-pressure source the attenuation is about a factor of three. © 2011 American Institute ofPhysics. [doi:10.1063/1.3639128]A plethora of UV light sources exists in the 250 to350 nm range. However, many of these either have a low lumi-nous intensity (e.g., deuterium lamps), pulsed operation (e.g.,most frequency quadrupled Nd:YAG lasers), or high price(e.g., He-Cd gas lasers or XeCl excimer sources).Within the field of TiO2-based photocatalysis in general– and TiO2-based self-cleaning surfaces in particular – it isof interest to explore how activity scales with the thicknessof the photocatalytic material.1 This is especially true whenthe photocatalytic material is illuminated from the back-sidewith respect to the reactants since in that case there exists a(wavelength dependent) optimum film thickness.2, 3 In orderto obtain an intermediate penetration depth of the photons insuch an experiment using a TiO2-based photocatalyst (bandgap of Eg ≈ 3.2 eV (387 nm)) a photon energy E = Eg + where  ∈ [0.5, . . . , 1.0] eV (335. . .295 nm) is needed (at365 nm the 1/e penetration depth into a TiO2 film is on theorder of ∼1 μm (!)). The 295. . .335 nm range is also suitedfor the Pyrex-lids used in our μ-reactors4, 5 in which we wishto perform the photocatalytic measurements. A light sourcewith the following characteristics is therefore sought: Main emission between 295 and 335 nm. Negligible emission below 290 nm and between350 nm and 380 nm. Delivered irradiance of at least 100 mW/cm2 over a10 mm circular sample. Continuous illumination (CW source). Reasonable cost.Review of commercially available sources indicate thatthe simplest solution would be a He-Cd gas laser operating at325 nm. He-Cd lasers of adequate power, however, are quitea)Electronic mail: Peter.Vesborg@fysik.dtu.dk.b)Electronic mail: ibchork@fysik.dtu.dk.c)Electronic mail: theisn@kiku.dk.expensive. The low throughput of monochromators rule outbroadband sources such as Xe-arc lamps. An alternative op-tion would be to use a Hg-arc lamp and use the light at oraround the 313 nm line, which is strong in Hg-sources at ele-vated pressure, but this requires that the (even stronger) broademission line around 365 nm is filtered away without dampingthe 313 nm line significantly. While commercial holographicnotch filters with an optical density of ∼4 are available for365 nm the holographic medium itself has an unacceptablylow transmittance around 313 nm (typically below 10%)which unfortunately precludes such filters from the presentapplication.The lanthanides are known for their narrow absorptionlines arising from f-f transitions.6–9 In particular, holmium ispopular as a calibration standard for spectrophotometers. Al-though Ho3+ has a low absorption around 313 nm, its line at361 nm is too far from the 365 nm line in Hg to be of use forthe present purpose.Dy3+, on the other hand, has an absorption spectrumwhich is nearly ideally suited for absorbing the unwanted Hgline. Dysprosium triflate (Dy(CF3SO3)3) was chosen for thefiltering due to the high solubility and the stability of the com-pound. The salt was prepared by slowly adding 0.445 moles ofconcentrated triflic acid (100 %) to a suspension of 0.15 molesof Dy2O3 in 400 ml of water in a beaker (1000 ml) over a pe-riod of ∼10 min whereupon the mixture was boiled overnight.The following day, the surplus of dysprosium oxide was fil-tered off and the supernatant was concentrated under reducedpressure until the salt Dy(CF3SO3)3 · 9H2O precipitated. Thesalt was isolated on a sintered glass funnel and washed threetimes with diethyl ether to remove the remaining water. Theproduct was dried in a desiccator over P4O10. The purity ofthe product was checked by an EDTA titration of dysprosium,which confirmed the presence of 9 water molecules.A cylindrical quartz cuvette of 20 mm optical pathlength filled with a solution of 0.81 M dysprosium triflate0034-6748/2011/82(9)/096102/3/$30.00 © 2011 American Institute of Physics82, 096102-1Downloaded 11 Nov 2011 to 192.38.67.112. Redistribution subject to AIP license or copyright; see http://rsi.aip.org/about/rights_and_permissions096102-2 Vesborg et al. Rev. Sci. Instrum. 82, 096102 (2011) 0 20 40 60 80 100Transmittance (%)Transmittance 0 0.5 1 1.5 2 2.5200 300 400 500 600 700 800 900Abs. unitsWavelength (nm)Absorbanceab cdef ghi jkFIG. 1. (Color online) Absorbance and transmission spectrum ofDy(CF3SO3)3 · 9H2O dissolved in methanol.in methanol was used for the filter. Figure 1 shows theabsorbance of a dysprosium triflate filter as measured usinga spectrophotometer. Main features in the 190 nm to 900 nminterval are labeled with letters a through k. Also plotted isthe transmission spectrum which clarifies where the filter hasits absorption lines.Table I shows quantitative data from the UV-VIS spec-trum shown in Figure 1. Columns 3 and 4 show the peakabsorbance and the corresponding algebraic damping factor,respectively. The latter four columns show the wavelengthsfor which the absorbance or damping is half the peak value.This can be used for peak-width estimation (e.g., FWHMvalues) and peak symmetry estimation. Main absorption linesare a, d, f, g, and k, where g at 365 nm is the one that isuseful for the present purpose. The other lines are weaker.A low-pressure Hg light source is made from an ar-ray of 4 low-pressure Hg tubes (8 W each) and Figure 2TABLE I. List of important absorption peaks in Dy(CF3SO3)3 · 9H2O dis-solved in methanol derived from the data shown in Figure 1. Am , denotesthe peak absorption (abs. units) and F denotes the attenuation factor (incidentintensity/transmitted intensity). λ(Am/2) values are the wavelengths for whichabsorption drops to half the peak value (in absorbance units) and λ(F/2) valuesare the wavelengths for which the attenuation factor has dropped to half thepeak value.Peaka Am b Fc λ(Am/2)a λ(F/2)aa 198.0 2.90 800 ... ... 193.0 203b 256.5 0.76 5.8 255.5 258.5 255.5 258.0c 295.0 0.83 6.7 293.0 296.0 294.0 296.0d 325.5 2.00 98 323.5 327.0 324.5 326.0e 338.0 0.47 3.0 336.0 340.0 335.0 340.5f 351.0 2.15 140 348.0 353.5 349.0 353.0g 365.0 2.30 200 363.0 367.0 364.0 365.5h 387.5 1.26 18 385.0 391.0 386.0 389.0i 453.0 0.42 2.6 447.5 455.5 446.0 457.0j 756.5 0.49 3.0 751.5 763.5 750.5 765.0k 806.5 2.44 280 801.5 812.0 804.5 808.5aUnits are in nm.bAbsorbance units.cNo unit. 0 0.2 0.4 0.6 0.8 1 250  300  350  400  450  500  550  600Irradiance (A.U.)Wavelength (nm)No filterDy3+ filter 0 0.01 0.02 0.03 300  325  350  375  400 0 0.2 0.4 0.6 0.8 1 250  260FIG. 2. (Color online) Measured spectra of a low-pressure Hg-dischargelamp with and without the dysprosium filter. The main line at 254 nm isalmost unaffected by the absorption of the narrow b line at 256 nm, while theline at 365 nm is significantly dampened.shows the measured unfiltered spectrum and the spectrumof the same lamp, when filtered through the dysprosiumfilter. The irradiance measurement is carried out using aspectroradiometer. The measured data is normalized to theunfiltered Hg-line at 254 nm where irradiance is around0.624 mW/(cm2 nm). The integral of the 254 nm peak is1.96 mW/cm2 for this lamp.It is clear from Figure 2, that the dysprosium filter sig-nificantly and selectively dampens the line at 365 nm whileleaving the other main lines (including the main line at254 nm) largely unaffected. This makes the filter highly use-ful for low-pressure Hg-lamps, but the moderate irradiance(100 mW/cm2) makes it unsuited for the purposes of thephotocatalytic experiment.High-pressure Hg-lamps offer much higher radiance thanlow-pressure lamps and the emission lines at 304, 313, 333,406, and 437 nm become very intense. For applications where 0 0.2 0.4 0.6 0.8 1 250  300  350  400  450  500  550  600Irradiance (A.U.)Wavelength (nm)No filterDy3+ filterFIG. 3. (Color online) Measured spectra of a high-pressure Hg short-arclamp with and without the dysprosium filter. The total irradiance in the300. . .334 nm interval is dampened by a factor ∼0.74 while the interval from335. . .370 nm is dampened by a factor ∼0.32.Downloaded 11 Nov 2011 to 192.38.67.112. Redistribution subject to AIP license or copyright; see http://rsi.aip.org/about/rights_and_permissions096102-3 Vesborg et al. Rev. Sci. Instrum. 82, 096102 (2011)monochromatic light is needed, the very significant line-broadening, which also occurs, is of course unwanted. Forthe purposes of filtering away the dominant line at 365 nmwith Dy3+ the broadening of the emission is an importantlimitation since the absorption line remains quite narrow (seeTable I), but nevertheless a Dy3+-based filter may signifi-cantly attenuate the 365 nm line.Figure 3 shows the influence of the Dy3+ filter on a highpressure Hg source.10 Integration of the spectra shows that inthe regions of interest (300. . .334 nm and 335. . .370 nm) in-sertion of the Dy3+ filter attenuates the light by a factor of∼0.74 in the desired region while the attenuation is a factorof ∼0.32 in the unwanted longer-wave region. Thus the over-all gain of using the Dy3+ filter is a factor 0.74/0.32 = 2.3.This, relatively cheap, light source provides a total incidentpower of ∼850 mW (300. . .335 nm), ∼500 mW (335. . .370 nm), and ∼4200 mW (370 nm ≤ λ) over a 1 cm2 areawhen the Dy3+ filter is used. For comparison, we note thatwhen the Dy3+ filter is not used the light source provides atotal incident power of about ∼1150 mW (300. . .335 nm),∼1600 mW (335. . .370 nm), and ∼4700 mW (370 nm ≤ λ)over a 1 cm2 area.CINF is funded by the Danish National Research Foun-dation. P. C. K. Vesborg is supported by DFF/FTP (ProjectNo. 10-080861).1M. Bouchy and O. Zahraa, Int. J. Photoenergy 5, 191 (2003).2D. Chen, F. Li, and A. K. Ray, Catal. Today 66, 475 (2001).3G. Camera-Roda and F. Santarelli, Catal. Today 129, 161 (2007).4T. R. Henriksen, J. L. Olsen, P. C. K. Vesborg, I. Chorkendorff, andO. Hansen, Rev. Sci. Instrum. 80, 124101 (2009).5P. C. K. Vesborg, J. L. Olsen, T. R. Henriksen, I. Chorkendorff, andO. Hansen, Chem. Eng. J. 160, 738 (2010).6J. Hoogschagen and C. J. Gorter, Physica 14, 197 (1948).7C. K. Jørgensen, Acta Chem. Scand. 11, 990 (1957).8W. T. Carnall, P. R. Fields, and K. Rajnak, J. Chem. Phys. 49, 4412 (1968).9W. T. Carnall, Handbook on the Physics and Chemistry of Rare Earths(North-Holland, Amsterdam, 1979), Chap. 24, pp. 171–208.10The high-pressure Hg-lamp is a Ushio model SMR-200UV3, 200 W short-arc lamp (1.2 mm arc) fitted with a water/Cu(ClO4)2 filter to absorb IRand coupled through a deep-UV liquid light-guide (Newport model 76842).The measured spectra have been normalized to the intensity of the 437 nmline without the Dy3+ filter. Note that this particular lamp (which Ushiohas fitted with an ellipsoid reflector with a selective coating) has almostno intensity at 254 nm. The apparent slightly negative irradiance at veryshort wavelengths is a measurement artefact which is due to the very shortintegration times used in the measurement of this intense source. We alsonote that the characteristic fluorescence lines of Dy3+ around 480 nm and572 nm are insignificant compared to the Hg-light.Downloaded 11 Nov 2011 to 192.38.67.112. Redistribution subject to AIP license or copyright; see http://rsi.aip.org/about/rights_and_permissions

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Note: Simple means for selective removal of the 365 nm line from the Hg spectrum using Dy

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