`
`
`
`
`
`CHROMATICITY DIAGRAM
`
`TCL 1027, Page 1
`TCL 1027, Page ]
`
`

`

`Applied
`Optics
`
`VOLUME 10
`NUMBER 1
`JANUARY
`1971
`
`A monthly publication of the
`Optical Society of America
`
`J. N. Howard Editor
`
`P. R. Wakeling Managing Editor
`
`Cover: See page 153.
`
`Published monthly pyihe Optical Society of
`America at 20th and
`orthamptonStreets,
`Easton, Pa. 18042. Office of the Editor:
`AFCRL, Bedford, Mass.
`01730;
`617-861-
`4281. Office of
`the Managing
`Editor:
`WINC
`13° Nineteenth Street, N.W.,
`Washington,
`D.C.
`3
`202-387-1773.
`Advertising
`office: American Institute of
`Physics,
`335
`E. 45th Street, New York, N.Y.
`10017; 212-MU 9-1940. Subscription rates
`. Be ear:
`included in members mows te
`members; nonmembersand libraries
`- Single copies $4: complete volumes
`Bc Sap NTUSOBY he Soa
`ie
`opyri
`e
`Optica
`Society of Arnerice, Inc.
`*
`
`14
`
`19
`
`&&
`
`38
`eg 42
`46
`51
`
`65
`
`74
`
`81
`
`87
`99
`105
`
`109
`
`Nua
`119
`
`132
`136
`141
`
`144
`
`150
`
`154
`
`Sha
`168
`
`174
`
`Ni 182
`187
`
`193
`
`201
`
`14
`
`by
`f Color Matching
`Geodesic Chromaticity Diagram Based on Vari
`ee
`te
`Normal Goeertenon MacAdam
`A Visual Tristimulus Projection Colorimeter—A. Valberg
`Adjustment of the Munsell-Value and W*-Scales to Uniform Lightness Steps
`for Various Background Reflectances—C. C. Semmelroth
`Internal Reflection Spectroscopy: Validity of Effective Thickness Equations
`—N. J. Harrick and A.
`|. Carlson
`Hadamard-Transform Exhaust-Analysis Spectrometer—J. A. Decker, Jr.
`A Grazing Incidence Monochromator for Satellite Studies of the Solar Hell
`Lyman-c Lineat 303.8 A—P: J. Bowen, J. A. Bowles, W.M. Glencross,R. J.
`Speer, A. F. Timothy, J. G. Timothy, and A. P. Willmore
`A Convenient Technique for Determining the Relative oe Efficiency of
`a Monochromator and Detector System—J_ L. Kohl, L. J. Curtis, D. A.
`Chojnacki, and R. M, Schectman
`Motion Blurring with Decaying Detector Response—L,Levi
`Electrical Recording
`of the Amplitude and Phase Fluctuations of a Wave
`Front—M. Bertolotti
`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. DeLong
`Effects of Argon Atoms on the Self-Absorption and the oy of Hg 2537-A
`Radiation in Hg + Ar Discharges—T. J. Hammond and C.F. Gallo
`Statistical Band Model Parameters and Integrated Intensities for the 5.9-,,
`7.5», and 11.3 . Bands of HNO; Vapor—-A. Goldman, T. G. Kyle, and F. S.
`Bonomo
`Radiance and Polarization of Light Reflected from Optically Thick Clouds—
`G. W. Kattawar and G. N. Plass
`Radiation-Induced eee in Refractive Index and Absorption Coefficient
`for Several Optical Materials—D. R. Olson, H. D. Dieselman, and J. B.
`chroeder
`
`Dampingof Lattice Vibrations in Solids—J. N. Plendl
`The Correction of Optical Aberrations by Neutron Irradiation—P. Sinai
`ieraiee of Truncated One-Dimensional Periodic Bar Targets in Aberration-
`imited 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
`Small-Angle Scattering of Light by Ocean Water—tH, T. Yura
`Bidirectional Seater Characteristics of Healthy Green Soybean and Corn
`Leavesin vivo—H.
`T. Breece |Il and R. A. Holmes
`Cineholomicroscopy of Small Animal Microcirculation—M. E. Cox, R. G.
`Buckles, and D. Whitlow
`Calorimeter for Laser Energy Measurements—M. M. Birky
`The CO:Laser Signature Problem—P. C. Claspy and Yoh-Han Pao
`CO, Laserwith SimultaneousActive and Passive Q-Switching—O. M. Stafsudd,
`O. Ersoy, and S. Pizzica
`.
`Saito
`A Preven Variable, Double Prism Attenuator for CO, Lasers—T. Oseki and
`Photoluminescent Conversion of Laser Light for Black and White and Multi-
`color Displays.
`1: Materials—L. G.
`Van Uitert, 0. A. Pinnow, and J.C.
`Williams
`
`January 1971 / Vol. 10, No. 1 / APPLEORTEGAPage 2
`
`Photoluminescent Conversion of Laser Light for Black and White and Multi-
`color Displays. 2: Systems—D. A.
`innow, L. G. Van Uitert, and M.
`Feldman
`
`Measurementof the Beam Parameters of a Laser Beam and Its Diffraction
`Field, Using a Hologram—T. Miyamoto and K. Yasuura
`A Contribution to the Comparisonof Single Exposure and Multiple Exposure
`Storage Holograms—M. Lang, G. Goldmann, and P.Graf
`Hotegisptic Subtraction—K. Bromley, M. A. Monahan, J. F. Bryant, and B. J.
`hompson
`A Holographic Interferometer for Measuring Radiation Energy Deposition
`Profiles in Transparent Liquids—E. K. Hussmann
`A Generalized Technique of Two-Wavelen3jth, Nondiffuse Holographic
`Interferometry—F.
`Weig!
`A Technique for Recovering Doppler Line Profiles from Fabry-Perot Inter-
`ferometer Fringes of Very Low Density—P. 8. Hays and R. G. Roble
`Seer Visualization Device Allowing an Arbitrary Orientation of the Lines
`with Respect to the Scanning Direction—R. Grossin, M. Jannot, 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 numberof photoluminescent materials have been found to have properties that make them extremely
`useful for improving the qualityoflaser displays as well as offering simplifications for multicolor systems.
`Theprincipal 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 coherentlight. It is concluded that virtually any visible color may be achieved by photoluminescent
`conversion of a monochromatic blueorultraviolet laser beam.
`
`1.
`
`ibration can proceed bothradiatively by the emission of
`a photon and nonradiatively by, for example, a series of
`phononinteractions. A material is considered to be a
`phosphorif radiative emission is observed. The rela-
`tive strength of radiative transitionsis 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
`energyis 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.
`
`Introduction
`‘In a recent review of laser display technology Baker!
`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 adequatelight 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 monochromaticor limited color range laser
`sources can and will be developed.? The purpose of the
`present work is to show that a monochromatic laser
`source is satisfactory for white light and multicolor
`displays when advantageis taken of photoluminescence,
`the absorption of light of one wavelength and the sub-
`sequent, emissions at another wavelength. By prop-
`erly coating a viewing screen with existing organic and
`inorganic phosphorsit is possible to efficiently convert
`monochromatic blue or ultraviolet
`laser light
`into
`virtually any visible color including white. An addi-
`Il. Characterization
`tional benefit. of this conversion is the elimination of
`There are four basic properties that characterize
`the unpleasant granular texture generally associated
`photoluminescent materials.
`‘They are (1) absorption
`with direct viewing of diffusely scattered coherent
`and emission spectra,
`(2) conversion lifetime,
`(3)
`light,® because the converted light is incoherent.
`quantum efficiency, and (4) absorption cross section.
`The basie physics of photoluminescent conversion is
`It should be noted that the last three properties can be
`quite simple. Photons from a light beam such as a
`funetions of the exciting wavelength. The features
`laser beam are absorbed in a material which is thereby
`that make a phosphor desirable for application in laser
`raised to an excited state. This excitation equilibrates
`display systems can be related to these properties.
`inabrief interval, typically 10~* sec to 10-* see. _Equil-
`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 ascreen. The phosphor should
`have an emission spectrum in a desired wavelength
`
`The authors are with Bell Telephone Laboratories, Inc., Mur-
`ray Hill, New Jersey 07974.
`Received 16 March 1970.
`
`150 APPLIED OPTICS /Vol. 10, No.1 / January 1971
`
`TCL 1027, Page 3
`TCL 1027, Page 3
`
`

`

`STRENGTH
`RELATIVE
`
`N
`
`yc EMIssto
`
`ae 000
`
`4000
`
`5000 ~
`WAVE LENGTH(A)
`
`6000
`
`TO00
`
`Fig. 2. Relative absorption and emission spectra of YAG:Ce.
`The broad absorption band is due to a d-band excitation.
`
`-
`
`It is possible to achieve other colors by photolumines-
`cent conversion using different rare-earth ions. For
`example, Sm‘* has a peak emission at 5980 A, Eu®t at
`6140 A, Dy*+ at 5740 A, and Er’+ at 5520 47 How-
`ever, none of these transitions other than those for Tb*+
`can be directly excited to any extent by the 4880-A line
`of
`the argon laser. Generally, shorter wavelength -
`excitation is required. However, indireet excitation of
`Eu’+ is possible through an intermediate Tb'+ ion.$
`For example, excitation transfer from Tb*+ to Eu?+ in
`Nap.sT'bp.2sEuy.2sWOs causes this material
`to emit a
`strong red color under 4880-A illumination. The ab-
`sorption bands of Tb*+ and Eu*+ 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.;Tbo.5-
`WO,discussed above.
`_
`The Ce’* and Eu?+ 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.° A rather unusual but useful material
`is made by adding cerium to Y3Al;0;; (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-A
`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
`YAGhost.
`In addition to this relatively large absorp-
`tion cross section, this compound has a very shortlife-
`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 display screen
`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
`Al with Ga causes the opposite effect.° Other Ce3+ and
`Eu’* compositions that have been investigated®”
`require excitation at wavelengths substantially shorter
`than 4880 A, enerally in the ultraviolet.4
`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 / APPLIED OPTICS 151
`
`Te
`
`_
`
`So
`
`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.®
`Finally, the phosphor should beinexpensive,stable, and
`preferably nontoxic.
`
`lll. Materials
`
`Rather than attempting to cover the broad field of
`phosphors, we will discuss, by way of particular ex-
`amples,
`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 compoundsthatare
`activated by transition metals and other organie mate-
`rials such as the aromatic hydrocarbons.
`
`A.
`
`_
`
`SSTST
`
`|
`
`Inorganic Phosphors
`According to Pringsheim,* 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 ionsare 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 Tb*+ is a particularly useful ion since
`the wavelength for maximum absorption of its ®D,
`manifold corresponds quite closely to the blue (4880
`) emission of the argon ion laser, When this ion is
`embeddedin 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 A?
`Thelifetime is approximately 0.5 msec,
`| and the quantum efficiency is high, approaching 1007.
`We have examined the performance of Napo.s'T'bo.;WO,
`A) and find
`_ under excitation by an argon laser (4880
`that 1l-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
`| sereen.
`
`ABSORPTION
`
`
`
`4880
`
`6000
`:
`WAVE LENGTH(A)
`
`xz=oe=zWwW
`
`4 &
`
`WwW
`
`2qai
`
`re)c
`
`t
`
`j Fig. 1. Relative absorption spectra of Tb?+ and Eu®t and the
`| emission spectra of Eu?t. When these two rare-earth ions are
`|
`included in the same host, such as Nag sTbo.25Eup,2sWO,, absorp-
`|
`tion ofargon laser radiation at 4880 A is due to Tb?+ while excita-
`|
`tion transfer to Eu*+ results in the characteristic Eu’+ emission
`spectrum which peaks in the red at 6140 A
`
`TCL 1027, Page 4
`TCL 1027, Page 4
`
`ée
`
`e
`
`

`

`Fluorescence
`Band
`Color
`
`uv
`
`2900-4600 violet
`(3200)
`strong
`4400-5200 5100-5900 yellow-green
`(4940)
`(5180)
`very strong
`4500-5600 5200-6000 yellow
`
`4800-6000 5500-7000 red
`(5500)
`(6050)
`strong
`4800-5900 5360-6020 yellow
`(5260)
`(5550)
`strong
`4550-6000 5600-6800 orange
`medium
`5400-5900 5600-6500 orange
`medium
`
`uy-5200
`uv-5400
`
`3000-4500 4000-4800 blue-violet
`medium
`4750-6400 green
`5050-6700 greenish-
`(5850)
`yellow
`medium
`4700-6500 green weak
`4850-6600 yellowish-
`green
`strong
`
`uv-5100
`uv-5000
`
`Compounds
`
`I. Xanthene
`Fluoran
`
`Rhodamine 6G
`
`Acridine red
`
`Pyronine B
`
`If. Acridine
`Acridine
`
`Acridine yellow
`Euehrysine
`
`i
`Rheonine A
`Acriflavine
`(Trypaflavine)
`
`III. Azine
`Magdala red
`
`Safranine
`IV. Thiazine
`Thionine
`
`dayglow phenomenon has found considerable use in
`Table |, Absorption and Fluorescence Bands of Dyesin
`advertising display and is due to strong absorp-
`
`
`Aqueousor Alcoholic Solutions, after Pringsheim*eesillslesterstietesesenmsarnnitianiaataanareesissaamie
`tion of blue and green light with subsequent emission
`First
`at the various longer wavelengths. '*
`absorption
`The fluorescing hydrocarbons and dyes are em-
`band
`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
`organie resin solution which is subsequently condensed
`Fluorescein
`to an insoluble state by the application of heat.’
`In
`(Dihydroxyfluoran)
`certain cases the efficiency is enhanced if the dyeis
`Eosin
`adsorbed on colloids such as fibers or gel particles of
`(Tetrabromofluo-
`high polymers.'* Representative materials and the
`
`rescein) (5400)—strong(5170)
`
`color which they fluoresce include pyrelene (blue),
`Erythrosin
`4600-5560
`5180-5880 yellow
`fluorescein (yellow-green), eosin (yellow), Rhodamine-B
`(Tetraiodofluo-
`5165
`53875
`weak
`(red), Rhodamine-6G (yellow), acridine (blue), acri-
`rescein)
`flavine (yellow-green), naphthalene red (red), Auro-
`5500-6700 orange
`(5438)
`Rose bengale
`(Tetraiodotetra- (6000)—very weak
`
`mine-O (yellow-green), and 7-diethylamino-4 methyl
`chlorofluorescein )
`coumarin (blue) as well as other xanthene, azine, oxa-
`Rhodamine B extra
`zine,
`thioazine, acridine,
`flavin, naphthalimide, and
`coumarinderivatives. Additional data on the absorp-
`tion and emissionof selected dyes are given in Table I.®
`We have examined in considerable detail a naph-
`thalimide
`dye,
`4-amino-1,8-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 Manu-
`facturing Company, Scotcheal Fluorescent Film, types
`3483, 3484, and 3485). Their emission spectra for
`4880-A excitation, which are shown in, Fig. 3, exhibit
`peaksat 5200 A (yellow-green), 6000 A (orange), and
`6200 A (red). We have determined that their lifetimes
`are all considerably less than 1 ysec, 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 essentiallyall the violet and blue
`and a portion of the green. We have estimated from
`analysis of reflection spectra reported by Ward'® that
`
`4000-6000 5500-7000 red strong
`(5240)
`(6000)
`(5390
`
`yellow-red
`
`orange
`4800-6300
`medium
`(5800)
`
`5500-7000Methylene blue red medium
`
`* Approximate limits of bands 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.!* We have not
`found these materials to be particularly useful since
`most are not readily excited by argon radiation or are
`of inadequate quantumefficiency.
`
`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 visible spec-
`trum. Under whitelight 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 / January 1971
`
`3485
`
`0.5
`
`
`
`
`
`RELATIVEEMISSIONINTENSITY
`
`° 5000
`
`§ 000
`5500
`WAVE LENGTH (A)
`
`6 500
`
`Fig. 3. Relative emission spectra of naphthalimide dye (3485)
`and Rhodamine dyes (3483 and 3484) due to excitation by the
`4880-A line of an argon laser.
`
`TCL 1027, Page 5
`TCL 1027, Page 5
`a
`
`

`

`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 pigmentis
`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 vellowish-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, !* which absorbs in the
`yellow and red.
`The result
`then is a tradeoff 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, ex-
`amination of pyrelene in dilute alcoholic solutions in-
`dicates that it is blue fluorescing whenexcited by short
`wavelength blue light such as 4579-A emission of an
`argon laser or the 4416-A emission of a cadmiumlaser,
`while it becomes green fluorescing under longer wave-
`length blue excitation such as the 4880-A 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 ofefficient 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
`fluoresce any color desired including white whenillumi-
`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 from
`green and red phosphors to achieve a similar color
`gamut.
`‘These concepts have been verified using an.
`argonion laser source which emitted only blue 4880-A
`radiation.
`In conclusion, photoluminescent conver-
`sion of a monochromatic laser source provides an attrac-
`tive means for achieving white andlight 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. Grodkiewiez, A. G. Dentai, and C.J.
`Schmidt for the growth and preparation of test samples
`and 5. R. Williamson for assistance in experimental:
`measurements.
`
`References
`1. C. E. Baker, IEEE Spectrum 5, 39 (December 1968).
`2. J. BE, Geusie, H. J. Levinstein, $. Singh, RB. G. Smith, and L:
`G. VanUitert, Appl. Phys. Lett. 12, 306 (1968).
`3. L.H. Enloe, Bell System Tech. J. 46, 1479 (1967).
`4. P. Pringsheim, Fluorescence and Phosphorescence (Intersci-
`ence, New York, 1949), pp. 1-10.
`5. J. D. Gould and W. L. Makous, Information Display 5,
`25 (November/December 1968).
`6. Ref. 4, pp. 285-289.
`7. L. G. Van Uitert, J. Electrochem. Soc. 114, 1048 (1967).
`8. L. G. Van Uitert and R. R. Soden, J. Chem. Phys. 36, 1289
`(1962).
`9. G. Blasse, W. L. Wanmaker, J. W. ter Vrugt, and A. Bril,
`Philips Res. Rep. 28, 189 (1968).
`10. G, Blasse and A.Bril, J. Chem. Phys. 47, 5139 (1967).
`11. G, Blasse and A. Bril, Appl. Phys. Lett. 11, 53 (1967).
`12. Ref. 4, pp. 594-645.
`13. Day-Glo Color Corporation, Cleveland, Ohio, Tech. Booklet
`No. 1170-A.
`:
`14. E.G. Bobalek and W. von Fisher, Organic Protective Coatings
`(Reinhold, New York, 1953), pp. 115-118.
`15. Ref. 4, p. 423.
`16. R. A. Ward, “The Day-Glo Daylight Fluorescent Color
`Specification System (Day-Glo Color Corp., Cleveland,
`Ohio).
`
`
`
`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 & diagram were 20n;
`the angular separations of points were 18°/n. The constant-hue loci shown correspond to
`radii separated by 18° in the én diagram.
`
`January 1971 / Vol. 10, No. 1 / APPLIED OPTICS 153
`
`TCL 1027, Page 6
`TCL 1027, Page 6
`
`