At first foray into glass-bending, shaping the form for photon excitation, I was captivated with the window into the guts of illumination. The gaseous properties of emittance would scintillate and pulse with energy transfer—at last able to visualize what was opaque beneath electrical cabling.
Having installed dozens of fluorescent neon art wallworks at New York galleries, my past experiences had been lacking that ionized intimacy with light-making, that phenomenological jouissance of kinetic, visiblized electron transfer; I would’ve described those even pinks, purples, and whites then as neither lush nor lurid, nor conflagrant. There was nothing torrid nor particularly active about, at the time, what I pondered could be akin to an extruded bulb. Years later, I understand mechanistically why I wasn’t attracted to them.
Phosphor-coated tubes achieve a consistent surface brightness, sterile of its aliveness. The cold opaqueness suits itself to commerce—the tradeoff of optimized lumen-wattage output and customized color range being an illuminated shell obstructing the gaseous volatility fundamentally unachievable by LEDs; perhaps just use LED ‘neon’ flex. To pre-empt my unfairly swift verdict, I needed more questions answered:
What is the developmental history of luminescent phosphors?
What are their mineral constituents, origins, and from what environments did we extract their source?
What is the life cycle of rare-earth phosphors like?
Are there ecological consequences to the extensive application of phosphors in more than cathode gas-discharge lighting, color plasma displays, fluorescents, and LED technology? What can be done with them at end-of-tube?
Is there an e-waste recycling equivalent for the physical recovery of finite mineral substances?
Intro to Phosphors
A phosphor is a photoluminescent material that absorbs higher energy wavelengths in and around the ultraviolet spectrum, and re-emits energy—essentially down-converts it, in a longer wavelength of visible light.
Powdered phosphors are applied to the inner surface of glass tubing, which are later filled with inert gas. Under electric current, the ionized gas plasma produces UV light, which we otherwise would not be able to visiblize, that excites the phosphors to transmiss color wavelengths. Phosphor-coated tubes output more total lumens than their uncoated equivalents because of this energy down-transmission into visible light, or fluorescence.1
Additionally, they alter the color range producible by a single gas:Europium–Yttrium compounds give red color; Tb–F–ZnS (terbium, fluorine, and zinc sulfide) for green, and Ce–Sr–sulfide (cerium, strontium) for blue. These compounds luminesce when activated by photons of higher energy than the visible spectrum.
Developmental History of Phosphors
The term phosphor originates from the Greek ‘Phosphors’ or ‘light bearer’ and the Greek name for the planet Venus. Phosphorescence—distinct from fluorescence for persistent luminescence after the removal of energy source—and thermoluminescence were noted by the ancient Greeks including Aristotle, and documented by alchemist Vincentinus Casciarolo of Bologna who in 1604 coined the term ‘phosphor’. The luminescent phenomena were further described by Hennig Brand in the discovery of the element phosphorus in 1669, before classes of mineral phosphors were determined by Eilard Wiedemann in 1888.
The first generation of phosphors discovered included fluorite and CaF2: Mn (fluorite doped with manganese) deployed for fluorescence, and zinc sulfide for glow in the dark pigment since the 1930s. The first fluorescent tubes used zinc beryllium silicate phosphors to produce white light. The Halophosphates were the next generation of improving lamp efficacy, or output-for-wattage. Low-cost calcium halophosphate coated tubes expanded the fluorescent market since their 1942 invention, with double the output of previous phosphors, but demanded increasing power consumption over time, as the phosphors degraded. These halophosphates were phased out for a third generation of lumen efficiency: the tri-phosphors.
The field of neon benefited from 1950s research to produce the color-TV tube, requiring intense fluorescent materials, such as the first rare-earth phosphor yttrium-vanadate, activated by europium to produce red. Still used today to create “coral pink” neon, this phosphor is in almost every computer and TV screen. Newly discovered fluorescent phosphors for television expanded the range of neon lighting colors by 24 in the 1960s.
Following the energy crisis, early-80s demand for low-consumption light sources brought a new surge of research in luminous materials for high-efficiency fluorescent fixtures. These modern fluorescent compounds increased the color range available for neon tubing to almost 100. 6
In 1993, with the pressure demand for high luminance and long phosphorescence alternatives to radioactive promethium, Yasumitsu Aoki of Nemoto & Co. developed strontium aluminate phosphors activated by europium, with 10 times the luminance and duration of zinc sulfide. Today, alkaline earth oxides and rare-earth phosphors are the standard in the market.
Deeply saturated color phosphors, blended and powder-coated in glass fixtures, displayed high efficiency in the conversion of UV light into visible wavelengths, at levels of 80-95 lumens per watt. Triphosphors combine a proportional blend of three distinct rare-earth phosphors specific to red (Yttrium-Europium), green (terbium), and blue (Europium) wavelength shifts to produce white light. 2, 8
These modern phosphors are specific not only to gas-discharge lighting in cold cathode tubes and fluorescent fixtures: their applications have become universalized across CRTs, plasma displays, LCD screens, lasers, medical imaging, and LED chip technology.
Modern Phosphor Compounds & Mineral Origins:
Structurally, contemporary phosphor composition involves a stable, optically inert host lattice or crystal compound and an activator, or dopant. Typical host lattice structures complete alkaline earth metal cations with silicate, borate, phosphate, aluminate, germinate, and oxide anion groups. Cations that work as activators for phosphors can be rare earth, transition metal, and S2 ions.
Phosphor retailer Neon Products Netherlands discloses compounds and activators for basic colors in contemporary powder-coated tubing: 8
Blue - SrCaBaMg Chloroapatite chemical composition (Sr,Ca,Ba,Mg)5(PO4)3Cl : Eu2+ [europium activator]
Green - Calcium Tungstate (CAT) chemical composition Ce0.65Tb0.35MgAl11O19 [cerium terbium activator]
Red - Yttrium Oxide (YOX) chemical composition Y2O3 : Eu3+ [europium activator]
While there are abundant choices for optically inert host lattice compounds, we must turn critical attention to their much more limited modern activators. The current phosphor market is reliant on rare earth mineral activators without comparable performance substitutions. Especially as we globally transition from incandescent and fluorescent illumination —and away from plasma & LCDs to upwardly large LED displays—in the pursuit of ‘high-efficiency’ LED technology accepted as fossil-fuel reduction, we are also growing the market demand for phosphors deployed in their updated counterparts. We are growing the market for rare earth activators, a finite extract from our living lithosphere’s precarious crust.
In addition to their role as catalysts in oil refining and diesel additive, in fuel cell alloys, in magnets for electric motors and wind turbine generators, the predominant consumption category for rare earth elements are applications in Glass & Electronics. 36,000 annual tonnes in 2008 of Cerium, Europium, Gadolinium, Lanthanum, Neodymium, Terbium, and Yttrium were consumed in the manufacture of display phosphors (fluorescents, LCD and plasma screens, cathode ray tubes, medical imaging); lasers; fiber optics; glass polishing and tinting.
When we suss out the sources of these rare earth ores, I must drop my survey scholastics for my vendetta. I am a transplant from Baotou, Inner Mongolia, the world’s leading supplier of rare earth minerals and site of the radioactive tailings dam triple the size of Central Park. The pockmarks of open pit extraction, leaching ponds, and wastewater cesspools of Bayan Obo mine are visible from space—the world’s largest rare earth lake. 50% of the global rare earth metal supply, annually, is produced / coerced from crust at state-operated Bayan Obo. Rare earth extraction is acid-intensive, ecologically toxic, and permeates respiratory and waterways to the degree of a human rights violation cascade. “For every ton of high-quality rare earth metal being produced, the facility creates many more tons of radioactive wastewater, acid waste, carbon dioxide, and other toxic emissions,” writes Julie Klinger in Rare Earth Frontiers (2017). The mineral-metal hardware and health costs of connectivity in our device-illuminated globality, are borne not by the corporate profiteers of technocapitalism, but by the land and by labor.
“I can tell who was born and raised downstream of the mine because they often have skin lesions, thinner hair, brown teeth, and bone deformities. It’s infuriating, because their suffering was entirely avoidable,” states Klinger. Yet, I would venture to ask how we hold the scions of designed obsolescence accountable. 7 billion smartphones have been produced since Steve Jobs released the first iPhone. Purchase rate of a new smartphone for consumers in the industrialized world is, on average, every 2 years. The production phase of a smartphone represents 90% of the direct energy consumption of a smartphone throughout its entire lifecycle; electronic devices are made up of thousands of components, rare metals and rare earth elements (40 on average for a smartphone)11 which are extracted and refined using environmentally-intensive processes in locales with lower social standards including human rights. The story of modern phosphor displays and illuminant technology is inextricably one of exported unlivability.
In 2019, the US re-opened its only rare earth mine at Mountain Pass, CA, which closed mining in 1998 and ceased operations since 2002, due to wastewater cleanup litigation costs and multiple chapter 11 bankruptcies. According to annual US Geological Survey reports, this hedge-funded venture continues today to export all 28,000 metric tons of oxide ore for outsourced processing, none handled domestically—and then, re-import them from China refined as rare earth metals and alloys.
Application Trends Forecast for Fluorescent & Gas Discharge Lighting, LEDs, Displays: Efficiency Fallacy leads to greater Consumption 2
The call at-large for ‘greener’ efficient technology operates on the contingency that higher performance results in system-wide energy savings as ‘reduced consumption.’ However, to paraphrase David Owen in Annals of a Warming Planet, the historical evidence suggests that efficiency optimization reduces consumer cost to drive global adoption. Superseding the Department of Energy’s Efficiency Savings forecasts of both 2011 and 2018, we consistently expand new usage, because consumption becomes only more economical, no less attractive.
Market forecasts for the rare-earth phosphor industry reflect this phenomena. The market driver for low-power draw has only proliferated more advanced, refining-intensive rare-earth display phosphors to sustain luminous vividity for less wattage. As Owen writes, “The correlation between growth in efficiency and growth in consumption is not accidental.” LED technology’s ever-reaching popularity means the demand for rare earth phosphors is projected to grow rapidly, scalable far beyond their deployment in fluorescent tubes, and without accounting for the true environmental and human costs of their production.
End-of-Life / End-of-Tube: E-waste recycling, landfill, ecological impact
Japan Recycles Rare Earth Minerals From Used Electronics
Hydrometallurgical Recovery Process of Rare Earth Elements from Waste, Namil Um, InTechOpen (2017).
“In France, the Rhodia group runs two factories, in La Rochelle and Saint-Fons, that will recycle an estimated 200 tons of rare earths a year from used fluorescent lamps, magnets and batteries.”