January
`
`1971
`
`
`
`
`
`
`:3
`C)
`.+_
`93.00
`
`+
`0.10
`
`WEED
`
`1'
`[LED
`
`CHROMATICITY DIAGRAM
`
`TCL 1027, Page 1
`TCL 1027, Page '
`
`

`

`Arnontmy pubHcafion ofthe
`
`Opticai Society of America
`
`J. N. Howard Editor
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`P. II. Waltellng Managing Editor
`
`Cover: See page 153.
`
`Published monthly b the Optical Society of
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`\114
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`m
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`\i 132
`131
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`1:3
`
`2111
`
`VOLUME 10
`NUMBER 1
`
`JANUARY
`
`1971
`
`Geodesic Chromaticity Dia ram Based on Variance: of Cola! Hatching by 1‘
`Normal Observers—D.
`. MacAdam
`
`A Visual Tristimuius Projection Colorimeten—A. Vaiberg
`Adjustment of the MunseII—Value and WhScales to Uniform Lightness Steps
`for Various Background Reflectance—C. C. Semmelroth
`internal Reflection Spectroscopy: Validity of Effective Thickness Equations
`-—N. J. Harrrck and A. I. Carlson
`
`Hadamard-Translorm Exhaust-Analysis Spectrometer—J. A. Decker. Jr.
`A Grazing Incidence Monochromator for Satellite Studies of the Solar Hell
`Lyman-a Lineat 303.8 A—PT J. Bowen. J. A. Bewies, w. M. Glencross. R. J.
`Spear, A. F. Timothy. J. G. Timothy. and A. P. Wiilmore
`A Convenient Technique for Determining the Relative uantum Efficiency of
`a Monachromator and Detector System—J. L. Ko i. L. J. CurtisI D. A.
`Choinacki. and R. M. Schectman
`Motion Blurring with Decaying Detector Response—:1“ Levi
`Electrical Recordin
`of the Amplitude and Phase Fluctuations of :1 Wave
`Front—M. Berta otti
`
`A Simple Double Beam Accessory for Absorption spectroscopy—K. Leutwein
`Spectral Absorption Characteristics of the Major components of Dust Clouds
`——D. F. Flanigan and H. P. Belong
`of Hg 2537-A
`Effects of Argon Atoms on the Self-Absorption and the Intanai
`.Gailo
`Radiation in Hg + Ar Discharges—T. J. Hammond and C.
`Statistical Band Model Parameters and intog rated Intensities for the 5.9-...
`Bonor‘no
`7.5 p. and 11.! ,u Bands of I-INOa Vapor—A. Goldman, T. G. Kyle. and F. S.
`
`Radiance and Polarization of Light Reflected from Optically Thick Clouds—
`G. W. Kattawar and G. N. Plass
`
`Radiation-Induced Changes in Refractive Index and Absorption Coefficient
`for Several Optical
`aterlais—D. R. Olson. H. D. Dieselman, and .l. B.
`Schroeder
`
`Damping of Lattice Vibrations in Solids—J. N. Plendi
`The Correction of Optical Aberration: by Neutron Irradiation—P. Sinai
`Images of Truncated One-Dimensional Periodic Iar Targets in Aberration-
`irnited Optical Systems—J. W. Foreman, Jr., G. H. Hunt,and E. K. Lawson
`Influence of Scattered Radiation on Narrow Field of View Communication
`Links—D. E. Setzer
`
`Smelt-Angle Scattering of Light by Ocean Water—H. T. Yura
`Bidirectional Scattering characteristics of Healthy Green Soybean and Corn
`Leaves in viva—H.
`Breece ill and R. A. Holmes
`Cineholomicroscopy of Small Animal Microcirculatien—M. E. Cox. R. G.
`Buckles, and D. Whitlow
`
`Calorimeter for Laser Energy Measurements—M. M. Birky
`The CD: Laser Signature Problem—P. C. Claspy and Yoh-Han Pao
`co. Laser with Simultaneous Active and Passive 0-switching—0. M. Stafsudd.
`O. Ersoy, and S. Pizzrca
`.
`l o
`A Prsecgsaign Variable, Double Prism Attenuator for ca. Lasers—T. Oseki and
`Photolurninescent Conversion of Laser Li ht for Black and White and Multi-
`color Displays.
`1: Materials—L. G.
`an Uitert. D. A. Pinnow. and J- C-
`Williams
`
`Photcluminescent Conversion of Laser L ht for Black and White and Multi-
`Feldman
`coior Displays. 2: Systems—D. A.
`innOW, L. G. Van Uitert, and M.
`
`Measurement of the Beam Parameters of a Laser Beam and Its Diffraction
`Field, Using a Hologram—T. Miyamoto and K. Yasuura
`A Contribution to the Com arisen of Single Exposure and Multiple Exposure
`Storage Holograms— . Lang. G. Goldmann. and P. Graf
`Holo raphic Subtraction—K. Bromley, M. A. Monahan, J. F. Bryant, and B. .i.
`hor'npson
`
`January 1971 / Vol. 10. No. 1 / APPLIEq‘etfl'mnfipage 2
`
`raphic Interferometer for Measuring Radiation Energy Deposition
`A Hol
`Pro ilas in Transparent Liquids—E. K. Hussmann
`A Generalized Tachnfflue of Two-Wavelength, Nondlfluse Holographic
`Interferometry—F.
`eigl
`A Technique for Recovering Doppler Line Profiles from Peary-Perot Inter-
`ferometer Fringe: of Very Low Density—P. B. Hays and R. G. Roble-
`Schlieren Visualization Device Allowing an Arbitrary Orientation of the Lines
`with Respect to the Scanning Direction—R. Grossin, M. Jan not. and S.
`Viannay
`
`TCL 1027, Page 2
`
`

`

`PhOtoluminescent Conversion of Laser Light for
`Black and White and Multicolor Displays. 1: Materials
`
`L. G. Van Uitert, D. A. Pinnow, and J. C. Williams
`
`A number of photolurninescent materials have been found to have properties that make them extremely
`useful for improving the quality of laser displays as well as offering simplifications for multicolor systems.
`The principal function of these materials is that of color conversiOn when coated onto a laser illuminated
`viewing screen. A secondary, yet significant, role is that of rendering the converted light incoherent.
`This eliminates the unpleasant granular or speckly texture associated with direct viewing of diffusely scat-
`tered coherent light. It is concluded that virtually any visible color may be achieved by photoluminescent
`conversion of a monochromatic blue or ultraviolet laser beam.
`
`I.
`
`Introduction
`
`- In a recent review of laser display technology Baker1
`pointed out that considerable motivation in this field
`stems from the promise of producing a cathode ray tube
`type of display with essentially unlimited screen size.
`He concluded that although adequate light beam modu-
`lation and scanning techniques are presently available,
`broadly applicable equipment awaits the development
`of an efficient multicolor laser source.
`Although such a multicolor source would indeed be
`desirable, the prospects for its realization, even in the
`distant future, are speculative. However, it is clear
`that efficient monochromatic or limited color range laser
`sources can and will be developed.2 The purpose of the
`present work in to show that a monochromatic laser
`source is satisfactory for white light and multicolor
`displays when advantage. is taken of photoluminescence,
`the absorption of light of one wavalength and the sub-
`sequent emissions at another wavelength. By prop-
`erly coating a viewing screen with existing organic and
`inorganic phosphors it is possible to efficiently convert
`monochromatic blue or ultraviolet
`laser light
`into
`virtually any visible color including white. An addi-
`tional benefit of this conversion is the elimination of
`the unpleasant granular texture generally associated
`with direct viewing of diffusely scattered coherent
`light,3 because the converted light is incoherent.
`The basic physics of photoluminescent conversion is
`quite simple. Photons from a light beam such as a
`laser beam are absorbed in a material which is thereby
`raised to an excited state. This excitation equilibrates
`in abrief interval, typically 10"“ sec to 10 ‘3 sec. Equil-
`
`The authors are with Bell Telephone Laboratories, Inc., Mur-
`ray Hill, New Jersey 07974.
`Received 16 March 1970.
`
`150 APPLIED OPTICS I Vol. 10. No.1 I January 1971
`
`ibration can proceed both radiatively by the emission of
`a photon and nonradiatively by, for example, a series of
`phonon interactions. A material is considered to be a
`phosphor if radiative emission is observed. The rela—
`tive strength of radiative transitions is specified in terms
`of the phosphor’s quantum efficiency, defined as the
`ratio of emitted photons to absorbed photons.
`In
`general, the energy of the emitted photons is less than or
`equal to the energy of the absorbed photon (Stokes’s
`law). That is, the color of the emitted light is either
`unchanged or shifted in the direction of longer wave-
`lengths.
`In certain limited cases anti—Stokes (shorter
`wavelength) emission is also possible when additional
`energy is supplied to the single photon excited state by
`other means such as thermal excitation or multiple
`photon absorption.‘
`In the present work we will con—
`sider only Stokes emitting phosphors which have suf—
`ficiently high quantum efficiencies to be of interest for
`laser display applications. Some emphasis will be
`placed on those materials that can be excited by the
`argon ion laser which is presently the most suitable
`source for a laser display system.
`
`ll. Characterization
`
`There are four basic properties that characterize
`photoluminescent materials. They are (1) absorption
`and emission Spectra,
`(2) conversion lifetime,
`(3)
`quantum efficiency, and (4) absorption cross section.
`It should be noted that the last three properties can be
`functions of the exciting wavelength. The features
`that make a phosphor desirable for application in laser
`display systems can be related to these properties.
`First, the phosphor must have a high absorption cross
`section for the exciting laser wavelength so that. nearly
`total absorption can take place in a thin layer of mate-
`rial that is coated onto a screen. The phosphor should
`haVe an emission spectrum in a desired Wavelength
`
`g
`
`TCL 1027, Page 3
`TCL 1027, Page 3
`.5
`
`

`

`r-'i'jmum
`
`,
`
`
`
`
`
`
`
`_.Il-v"-577v.-_.r_-L...I-_--.-.m;-
`
`range with a high quantum efficiency, say, 50% or
`greater, since the display screen size is limited by avail-
`able light
`intensity.
`In addition,
`the conversion
`lifetime should be sufficiently short so that the screen
`Will not be overly persistent;
`there is no perceptible
`consequence if
`the lifetime is exceptionally short-.5
`Finally, the phosphor should be inexpensive, stable, and
`preferably nontoxic.
`
`Ill. Materials
`
`Rather than attempting to cover the broad field of
`phosphors, we will discuss, by way of particular ex—
`smples,
`those materials that We consider to be par—
`ticularly suitable for
`laser display systems. They
`generally fall into two categories, inorganic rare—earth
`phosphors and organic dye phosphors. To a lesser ex-
`tent We will also consider inorganic compounds that are
`activated by transition metals and other organic mate—
`rials such as the aromatic hydrocarbons.
`
`A.
`
`Inorganic Phosphors
`
`LO
`
`ABSORPTi0N
`
`N
`
`/EMISSi0
`
`STRENGTH O I."
`RELATIVE
`
`03 000
`
`4 000
`
`'
`5 000
`WAVE LENGTH (S)
`
`6000
`
`T 000
`
`Fig. 2. Relative absorption and emission spectra of YAG:Ce.
`The broad absorption band is due to a dpband excitation.
`
`'
`
`It is possible to achieve other colors by photolumines—
`cent conversion using different rare-earth ions. For
`example, Sm3+ has a peak emission at 5980 A, Eu3+ at
`6140 A, Dy3+ at 5740 A, and Er3+ at 5520 is How—
`ever, none of these transitions other than those for Tb“
`can be'directly excited to any extent by the 4880—3 line
`of
`the argon laser. Generally, shorter wavelength -_
`excitation is required. However, indirect excitation of
`En“ is possible through an intermediate Tb3+ ion.“
`For example, excitation transfer from Tb3+ to Eu3+ in
`Nap.5Tbo-25Eu0-25WO4 causes ghis material
`to emit a
`strong red color under 4880-A illumination. The ab-
`sorption bands of Tb3+ and Eu3+ and the emission of
`Eu“ are displayed as a function of wavelength in Fig.
`1. The absorption cross section, quantum efficiency,
`and lifetime of this material are similar to Nao.5Tbo.5—
`W04 discussed above.
`.
`The Cea + and Eu2+ ions are exceptions to the general
`observation that the fluorescence of rare—earth ions is
`little affected by the host. This is so because their
`emissions are from d—bands which strongly interact with
`the crystal field.9 A rather unusual but useful material
`is made by adding cerium to Y3A15015 (YAG): The
`lower excited states of the crystal field components of
`the 5d configuration of the YAG:Ce composition are
`sufficiently low in energy that absorption of 4880-3
`light becomes appreciable.“ Figure 2 shows the ab—
`sorption and emission spectra in detail. Note that the
`peak of the emission spectrum occurs at 5500 A, the
`wavlength at which the” eye is most sensitive. We
`have found that at 4880 A the absorptiOn cross section
`is approximately 30 dB/mm/wt % of Ce added to the
`YAG host.
`In addition to this relatively large absorp-
`tion cross section, this compound has a very short. life-
`time of approximately 0.07 ,usec (Ref. 11) and a quan-
`tum efficiency of approximately 70%.” These proper-
`ties make YAG:Ce very attractive for displayscreen
`applications. Furthermore,
`this material may be
`tuned for a particular use. By replacing some Y with
`Gd the peaks of the absorption and emission spectra
`shift to somewhat longer wavelengths, while replacing
`A1 with Ga causes the opposite effect.10 Other Ce3+ and
`Eu2+ compositions that have been intrestigatedl-1n
`require excitation at wavelengths substantially shorter
`than 4880 it, generally in the ultraviolet“
`In addition to the rare-earth compounds, there are
`large classes of inorganic phosphors which have II—VI
`hosts such as ZnS and activators such as 'Bi, Mn, Cu,‘
`
`January 1971 / Vol. 10. No.1 f APPLIED OPTICS 151
`
`.-5,5—4-r-,qn.‘.-.r.-
`
`According to Pringsheim,‘i practically all molecules
`that are photoluminescent
`in condensed states are
`rather complex. The only exceptions are the positive
`ions of some rare—earth metals. The optical properties
`of these ions are so little perturbed by the surrounding
`medium that, even in crystals, they behave almost like
`isolated atoms, and their energy levels are well known?
`The rare-earth Tb3+ is a particularly useful ion since
`the Wavelength for maximum absorption of its 5D,,
`manifold corresponds quite closely to the blue (4880
`A) emission of the argon ion laser. When this ion is
`embedded in a properly chosen host, such as a tungstate
`or a molybdate, it will emit upon excitation a strong
`greenish-yellow color which has a peak at approximately
`5440 K7
`The lifetime is approximately 0.5 msec,
`and the quantum efficiency is high, approaching 100%.
`We have examined the performance of Na .5Tbo.5WO.;
`under excitation by an argon laser (4880 g.) and find
`that l-mm thick sample absorbs approximately 50%
`' of the incident beam. This absorption cross section is
`substantially lower than optimum since a considerable
`' thickness of material would be required to coat a display
`;- screen.
`
`
`
`r-.~._,,-._—-'.'4.-"":I'.'
`
`'
`
`ABSORPTION
`
`
`
`' 0000
`.
`wave LENGTH (A!
`
`I,_£92IJJ
`
`K t
`
`":
`I.”
`2.1I.“I
`
`2'
`
`_
`
`4 can
`
`Fig. 1. Relative absorption spectra of Tb” and E113+ and the
`" emission spectra of Eu“. When these two rare-earth ions are
`I'
`included in the same host, such as N84,5Tbo.2sEuo,25W04, absorp-
`-
`lieu of argon laser radiation at 4880 A is clue to Tb3+ while excita-
`:1
`tion transfer to En“ results in the characteristic EuH emiSsion
`spectrum which peaks in the red at 6140 A.
`
`.E
`
`‘
`
`TCL 1027, Page 4
`TCL 1027, Page 4
`
`

`

`_ Table l. Absorption and Fluorescence Bands of Dyes In
`______—.—_—-———
`Aqueous or Alcoholic Solutions, after Prlngshoimlfi'“
`First
`absorption
`
`Fluorescence
`
`dayglow phenomenon has found considerable use in
`advertising diaplay and is due to strong absorp-
`tion of blue and green light with subsequent emission
`at the various longer wavelengths.13
`The fluorescing hydrocarbons and dyes are em-
`ployed in very dilute form in order to achieve optimum
`quantum efficiency. Usually pigments (solid particles
`that carry dye) are formed by dissolving the dye in an
`organic resin solution which is subsequently condensed
`to an insoluble state by the application of heat.” In
`certain cases the efficiency is enhanced if the dye is
`adsorbed on colloids such as fibers or gel particles of
`high polymers.” Representative materials and the
`color which they fluoresce include pyrelene (blue),
`fluorescein (yellow—green), eosin (yellow), Rhodamine—B
`(red), Rhodamine—fiG (yellow), acridine (blue), acri-
`flavine (yellow-green), naphthalene red (red), Auro-
`mine-O (yellow-green), and 7-diethylamino-4 methyl
`coumarin (blue) as well as other xanthene, azine, oxa—
`zine,
`thioazine, acridine,
`flavin, naphthalimide, and
`coumarin-derivatives. Additional data 011 the absorp-
`tion and emission of selected dyes are given in Table I. 1"
`We have examined in considerable detail a naph-
`thalimide
`dye,
`4-amino-1,S—naphthal—p—xenylimide
`(yellow-green), and two Rhodamine dyes (orange and
`red) that have been cast into an adhesive coated plastic
`film for commercial use (Minnesota Mining and Mann-
`facturing Company, Scotchcal Fluorescent Film, types
`3483, 03484:, and 3485). Their emission spectra for
`4880-A excitatign, which are shown inc Fig. 3, exhibit
`peaksoat 5200 A (yellow-green), 6000 A (orange), and
`6200 A (red). We have determined that their lifetimes
`are all censiderably less than 1 usec, and their absorp—
`tion cross sections are so large that the entire laser beam
`is absorbed within the thin films which are approxi-
`mately 0.1 mm thick. Their absorption bands are
`quite broad, including essentially all the violet and blue
`and a portion of the green. We have estimated from
`analysis of reflection spectra reported by Ward” that
`
`I. Xanthene
`Fluoran
`
`Fluorescein
`(Dibydroxyfluoran)
`Eosin
`(Tetrabromofiuo-
`rescein)
`Erythrosin
`(Tetraiodofluo-
`rescein)
`Rose bengale
`(Tetraiodotetra-
`chlorofluoresccin)
`Rhodamine B extra
`
`Rhodamine 6G
`
`Acridine red
`
`Pyronine B
`
`II. Acridine
`Acridine
`
`Acridine yellow
`Euchrysine
`
`.
`Rheonine A
`Acriflavine
`(Trypafiavine)
`
`III. Amine
`
`Magdala red
`
`Bafranine
`1V. Thiazine
`Thionine
`
`uv
`
`290M600 violet
`(3200)
`strong
`5100—5900 yellow-green
`4400—5200
`(5180)
`very strong
`(4940)
`4500-5600 5200—6000 yellow
`
`(5170)
`4600*5560
`5105
`
`(5400)
`5180—5880
`5375
`
`strong
`yellow
`weak
`
`(5438)
`
`5500—6700 orange
`(6000)
`very weak
`
`red
`4800-6000 5500—7000
`strong
`(5500)
`(6050)
`4800~5900
`5360—0020 yellow
`(5260)
`(5550)
`strong
`455045000 5000—6800 orange
`medium
`
`5400—5900 5600-6500 orange
`medium
`
`3000—4500
`
`4000—4800 blue-violet
`medium
`
`uv—5200
`uv—5400
`
`uv—5100
`uv—5000
`
`4750—6400 green
`505043700 greenish-
`(5850)
`yellow
`medium
`4700—6500 green weak
`48504000 yellowish-
`green
`strong
`
`4000—6000
`(5240)
`(5390
`
`5500—7000
`(6000)
`
`red strong
`
`yellow~red
`
`orange
`480(Hi300
`medium
`'(5800)
`Methylene blue red medium 55004000
`
`
`
`
`' Approximate limits of hands in A; peaks of bands in
`parentheses.
`
`and Ag, and many activated tungstates, molybdates,
`vanadates, phosphates, germanates, and silicates that
`also have strong band fluorescence.12 We have not
`found these materials to be particularly useful since
`most are not readily excited by argon radiation or are
`of inadequate quantum efficiency.
`
`B. Organic Phosphors
`
`There are a number of aromatic hydrocarbons and
`organic dyes that when properly treated exhibit strong
`fluorescence over a broad portion of the vicible sper
`trum. Under white light illumination several of these
`appear to glow with a particular color ranging from
`greenish-yellow through orange to bright red. This
`
`152 APPLIED OPTICS / Vol. 10, No. 1 f January 1971
`
`/34ee
`
`3454
`
`3435
`
`'9
`
`0.5
`
`
`
`
`
`RELATIVEEMISSIONFNTENSlTY
`
`O 5 000
`
`§ 000
`5 500
`WAVE LENGTH [Al
`
`6500
`
`Fig. 3. Relative emission spectra of naphthalimide dye (3485)
`and Rhodarnine dyes (3483 and 3484) due to excitation by the
`4880—3 line of an argon laser.
`
`r
`
`TCL 1027, Page 5
`TCL 1027, Page 5
`I
`‘I-r:
`
`

`

`their quantum efficiencies are above 50%. Thus,
`these materials are almost perfectly suited for laser dis-
`play systems.
`'
`The colors of these fluorescing dyes may be modified
`somewhat by varying the type of carrier 'which is used
`to form pigments and, to a lesser extent, by varying
`the type of vehicle, or binder, into which the pigment is
`incorporated.
`It is also possible to modify colors by
`combining fluorescent dyes with nonfluorescent dyes
`that selectively absorb a portion of the emission spec—
`trum. For example,
`the emission spectrum of the
`naphthalimide dye (type 3485) show in Fig. 3 peaks at
`5300 A, in the green. Normally this fluorescence ap—
`pears to have a yellowish—green cast due to the broad
`tail of the emission spectrum which extends into the
`yellow and red. However,
`this tail can be substan-
`tially reduced by the addition of a nonfluorescing green
`toner such as phthalocyanine,‘3 which absorbs in the
`yellow and red.
`The result
`then is a tradeofi” of
`brightness for the ability to limit the spectral content.
`In contrast to the many yellow and red emitting dyes,
`blue emitting dyes are less common. However, ere
`amination of pyrelene in dilute alcoholic solutions in—
`dicates that it is blue fluorescing wheno excited by short
`wavelength blue light such as 4579—A emission of an
`argon laser or the 4410-A emission of a cadmium laser,
`while it becomes green fluorescing under longer wave—
`length blue excitation such as the 4880A line of an ar—
`gon laser.
`In addition, pigments of coumarin which
`fluoresces blue under near ultraviolet excitation are
`commercially available.”
`
`IV. Conclusion
`
`There exists a sufficiently wide range of efficient or-
`ganic and inorganic phosphors that can be excited by
`laSer wavelengths ranging from the ultraviolet to green
`and that have emission spectra covering the entire
`visible. For example, a suitable combination of blue,
`green, and red emitting phosphors can be made to
`fiuoresce any color desired including white when illumi-
`nated by a blue or ultraviolet laser source.
`If the
`
`source itself is blue, a portion of its intensity may be
`directly scattered and blended with the emission frond
`green and red phosphors to achieve a similar color
`gamut. These concepts have been verified using an.
`argon ion laser source which emitted only blue 4880—11
`radiation.
`In conclusion, photoluminescent conver—
`sion of a monochromatic laser source provides an attrac-
`tive means for achieving white and light and multicolor
`for display system applications.
`
`‘
`
`The authors acknowledge with thanks helpful dis-
`cussions with E. A. Chandross and C. V. Lundberg
`concerning organic dyes and pigments. The authors
`also thank H. W. Grodkiewicz, A. G. Dental, and C. J.
`Schmidt for the growth and preparation of test samples
`and S. R. Williamson for assistance in experimental
`measurements.
`
`References
`
`1. C. E. Baker, IEEE Spectrum 5.. 39 (December 1968)..
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`'
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`007.10:
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`13.
`'Day-Glo Color Corporation, Cleveland, Ohio, Tech. Booklet
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`'
`
`14. E. G. Bobalck and W. von Fisher, Organic Protect-ice Coatings
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`15. Ref. 4, p. 423.
`16. R. A. Ward, “The Day-Glo' Daylight Fluorescent Color
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`
`
`
`COVER
`
`This month's cover shows constant-hue and saturation loci derived from geodesic chroma-
`ticity diagram. The radii of the constant-saturation circles on the 5,» diagram were 20h:
`the angular separations of points were 18°ln. The constant-hue loci shown correspond to
`radii separated by 18“ in the 5,1, diagram.
`
`January 1971 / Vol. '10, No. 1 / APPLIED OPTICS 153
`
`TCL 1027, Page 6
`TCL 1027, Page 6
`
`