ZnCdS:Cu,Al,Cl: A Near Infra-Red Emissive Family of Phosphors for Marking, Coding, and Identification

Abstract

Zn 1-x Cd x :Cu 0.03% ,Cl (where x = 0.5-0.9) infrared emitting phosphors have been synthesized by an aqueous thermal decomposition method. The aim was to developing infrared emitting phosphors for coding, marking, and identification applications. The phosphors were characterized by, X-ray powder diffraction, scanning electron microscopy and photoluminescence spectroscopy. The emission band at 1000 nm was sufficiently far into the infrared region that visible emission was minimized. Co-doping Zn 1-x Cd x S:Cu 0.03% with Al 3+ increased the infrared emission intensity to over twice that of the equivalent Zn 0.3 Cd 0.7 S:Cu 0.03% phosphor (with no Al 3+ ion co-doping), with the highest intensity being found for the phosphor composition Zn 0.1 Cd 0.9 S:Cu 0.03%, Al 0.03% . It is shown herein that the inclusion of Al 3+ into the phosphors causes the formation of cells with smaller cell volume, and it is suggested that this is the prerequisite for the improved photoluminescent properties. Finally we have shown herein that these infrared emitting powder phosphors are thus able to meet marking and coding requirements, especially in low light and poor visibility. Although the uses of phosphors are widespread in modern technologies and they are common in the display and lighting industries where products find applications in both domestic and commercial applications, their use in other areas is less widely appreciated. Such uses include:-on postage stamps to help letter sorting, on currency and bank notes for secrecy/authenticity, thermometry, luminescent paints and glow in the dark toys. In addition there are a number of military applications.Recently the wide availability of near-ultraviolet light and visible light emitting diodes (LEDs) and laser diodes in addition to infrared emitting systems has made the remote excitation of infrared emitting phosphors a practical possibility. Infrared emitting powder phosphors have the potential to meet marking and coding requirements, especially in low light and poor visibility.The advantages of IR emitting powder phosphors are:-1) That they can be easily deposited by conventional techniques to form large areas, if required, either by simple settling techniques, or by inclusion in a binder suitable for screen or ink-jet printing (the binder of course must be transparent over the required spectral range). 2) Such deposited powder layers, depending on their thickness and particle size and particle morphology etc., can be used in a transmission or a reflective mode with suitable UV or visible excitation sources.The ease of fabrication and the wide excitation spectra of the phosphors as well as their efficiencies facilitate a wide range of potential applications, including the following as preliminary examples: a) For use in coding/marking systems as simple IR sensitive markers. b) For improved marking/detection in conjunction with night vision systems.The origins of the green luminescence in ZnS:Cu phosphors (where Cu is introduced as a dopant into the ZnS lattice) has been attribute...

Using liquid phase precursor method to create a high-efficiency Ca₂SiO₄:Eu²⁺ green-emitting phosphor

“…Rare-earth doped silicate phosphors have recently received a lot of attention because of their possible use in the white light-emitting diodes (WLEDs) and fluorescent lighting, both of these materials hold promise during the next solid-state lighting generation. The broad photoluminescent spectra, immense chemical stability and heat resistance, and reasonable synthesis cost are all important characteristics of silicate phosphors for many applications [1]- [3]. The divalent europium loaded the alkaline earth silicate phosphor structure is of specific importance because the ion radii of alkaline are earth ions, including 0.112 nm of [Eu 2+ ] and [Sr 2+ ], 0.099 nm of [Ca 2+ ], and 0.134 nm of [Ba 2+ ], are equivalent to those of the divalent europium.…”

Two-layer remote phosphor package as a solution to promote color quality scale and lumen in WLEDs

“…Researches have examined the silicate phosphors that generate blue and green light (BaZrSi3O9:Eu 2+ [5], [6] and Ba2MgSi2O7:Eu 2+ [7], [8], respectively) and employed them in near-UV LEDs. Furthermore, red Ca2Si5N8:Eu 2+ phosphors were also  ISSN: 2302-9285 made at standard pressure using the solid-state reaction approach [9]. For the current effort, near-UV chips of LED carry the task of pumping triple-chroma phosphors to create pc-WLEDs that yield considerable CRI values.…”

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Growth Kinetics of ZnS Thin Films from a High-Rate Chemical Bath Deposition with Trisodium-Nitrilotriacetate Complexing

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