Why is there a push towards phosphor free led technology?

Phosphors are a class of materials that absorb shorter wavelengths of light and emit longer wavelengths. They do this very very fast. Phosphors have allowed for a more compact led package. In phosphor based leds The active layer emits high energy wavelength. Some of this energy is absorbed by phosphor coating that converts it into low energy wavelengths. Thus result is that the overall energy radiating from the led package appears to be white. Mixture of blue, green, yellow, red. Before phosphors it was a common practice to use single colored LEDs. To produce white light then it was necessary to use atleast three LEDs. This was expensive,inefficient and a major reason why it took so long for leds to succeed even though they were discovered in early 1900s way before the invention of modern semiconductors. Phosphors have been revolutionary and yet there is a great deal of research being done to replace them why?

One reason is that they loose energy. The overall efficiency of the led package depends not only on the efficiency of the active emissive layer but also on the ability of the phosphor to convert the energy into different colors. The more layers you add to a system the less efficient it is going to get. Phosphors can be difficult to synthesize. Most of them are complex compounds of multiple elements. And because each and every led is coated with phosphors they need to be produced at scale. This complicates manufacturing process as not only do you have to synthesize active emissive layer but also the converting phosphor in equivalent quantity.

Many phosphor materials are made of rare earth materials. For something that is as important as an led you want to make it using materials that are abundant, easy to acquire recyclable. Long life span does not matter if the product is discarded and components are not recycled. Moreover you now have 2 points of failure in the system. The light source is going to stop working as intended if either the phosphor or the active emissive layer fails. It is for this reason that alternatives are being looked into.

Thats all well and good but what will phosphors be replaced with? So conceptually phosphors wont really be replaced. Pure materials are not capable of emitting white light. Band gap limits not just the amount of energy that can be absorbed but also the amount of energy that can be emitted. Since band gap is an intrinsic material property it follows that all materials would have a signature emission spectrum. As unique as a finger print. And sure enough spectral lines are proof that materials emit at well defined energies.

So while the concept of phosphors won't be replaced new kinds of phosphor technologies are being created. The most important of these are those that integrate with active emissive layer instead of being coated on the outer package of the led. So that in a single package we can have as close to white light emission as possible. Quantum dots, organic LEDs and donor/acceptors dopants in wide band gap semiconductor are some of the most promising ones.

We will be looking at these technologies and the research being done on them in future posts.

#light #energy #matter

Comments

Low energy fabrication of a high strength layered ceramic composite for high temperature oxidative environments

High temperature materials are required in various applications: in metallurgy, for making combustion chambers of internal combustion engines ,for the body of Stirling engines, for wall material of nuclear fusion reactors, for the body of Jet engines among a few. For such applications we need materials that can retain their strengths at elevated temperatures and can survive in an oxidative environment It is the second requirement which is more stringent. Although numerous metallic alloys have been synthesized that can sustain both high temperatures and oxygen attack they require complex processing steps On the other hand ceramics are good at resisting both oxygen attacks and high temperatures and are relatively simpler to fabricate but are limited by massive amounts of energy required. For example c/sic composites will perform well in demanding high temperature oxidative environments but require vacuum to be manufactured. The acheson process for the formation of sic is...

Force calculations on electron in vacuum tubes

ABSTRACT A claim was made in the paper titled “Do electrons really flow as a beam in cathode ray tubes? ” where we asserted that electrons remain near the cathode surface during the operation of CRT. Here we do force calculations on electrons by estimating the debye length of electrons emitted after thermionic emission and show that under given applied voltages if electrons are placed at debye length they are sufficiently far away from the cathode surface to be accelerated towards it. Debye length, while typically used to measure charge screening distance in plasmas and electrolytes, can also be used to estimate the distance of emitted electrons from the cathode surface. In the same way debye length is used to calculate the thickness of an electrical double layer in which the surface charge and charge on inner helmholtz plane are immobile & the charges on outer helmholtz plane are mobile we can model emitted electrons as mobile charges & image charges distribute...

Manufacturing technique for layered carbon /ceramic composite for use in high temperature oxidative environment

We previously described a layered carbon glass material system that is different from c/sic , c/sio2 matrix composites in that it consists of a distinct C/C phase which is coated by an sio2 layer. https://akshatjiwannotes.blogspot.com/2024/12/low-energy-fabrication-of-high-strength.html This material system presents a distinct advantage in a high temperature oxidative atmosphere as the C/C matrix is protected by the oxidation resistant glass shield. Such a material can supposedly be synthesized in an open oxidative atmosphere. In this short note we will answer some questions such as What manufacturing technique will be used? How can silica particles be sintered on the substrate? How can adhesion between sintered particles and carbon substrate be ensured? What, if any ,sintering aids will be used? What would be the mechanical properties of the composite so formed? What level of heat treatment will be required? To make the composite only the minimum amount of heat ...

Do electrons really flow as a beam in cathode ray tubes?

Abstract: It is generally well accepted that a beam of electrons flow from cathode to anode in a cathode ray tube. Taking pressure data from a variety of sources from CRT manufacturers’ data sheets to engineering documents of large hadron colliders we show through calculations that there is enough residual gas in these devices to form a conducting path from anode to cathode due to plasma formation. When high voltages are applied at the anode the gas is ionized and becomes a plasma forming a ‘wire’ between the two electrodes that causes conduction of energy. The objective of this brief note is to encourage scientists and engineers to re-investigate commonly accepted beliefs about vacuum tubes and develop new knowledge that can revitalize the field especially at a time when nano scaled vacuum channel transistors are being envisioned. Most vacuum tubes have operating pressures in the ultra high vacuum range. This is true for cathode ray tubes, vacuum tu...

Unlocking the Potential of Carbon for Long-Distance Electrical Transmission

ABSTRACT: We present a technique to manufacture large scale carbon based conductors for transmission of electrical energy over continental scale distances. We start by identifying precursors that could be used for production processes.We review the current manufacturing techniques of producing carbon based fibers and explain why certain precursors have dominated carbon materials industry. We identify methods that can be used to increase the yield through alternative precursors.We put forward a theory of why carbon conductors have less conductivity than metals and what can be done to improve it. Finally we postulate that with cheaper production methods even if carbon based conductors are 10 times less effective than poor metallic conductors like steel, they can still outperform them in High Voltage transmission lines if cheap manufacturing techniques could be developed. INTRODUCTION: Copper and in certain very specific applications aluminium & silicon steels dominate when it co...

What's with all the H1B ruckus?

The US policy makers are facing some tough choices as there's now an increased competition for talent from places like Europe,Australia,canada and even from asian nations like south korea , singapore ,saudi arabia ,UAE etc. While I'm all for protecting domestic jobs there's the danger that USA may face significant competition in the coming decades from the nations that are eager to hire talented immigrants to build their industry. The solution I think is to take lead in key industries to continue the growth. US did well initially with electric vehicles but it lost advantage. It has a lot going for it in AI and Google's quantum supremacy is promising for US deep tech. In semiconductors the chips and science act did well to promote local industries. US still has one of the largest fiber optic cable manufacturers. It's telecom industry is doing reasonably well. Boeing suffered some setbacks but other aviation components manufacturers like GE are doing well. Th...

Doping strategy for all carbon materials

The challange 1. Carbon is a very small atom. With an atomic number of 6, there are only 5 other atoms that are smaller than carbon. Compared to silicon with an atomic number of 14 the doping choices are minimal. Unlike silicon, elemental carbon can't be melt processed so existing tools & understanding about dopants (or more generally alloying) are out. 2. Carbon has a very rich chemistry. Elements like hydrogen & nitrogen that would become good candidates for doping actually form covalent bonds with carbon[1]. And instead of providing electron-hole pairs, the band gap continuously. Compare this with boron & phosphorus in silicon where they act more or less in their free atomic state. Sure with careful engineering maybe hydrogen & nitrogen can be made to fit inside carbon lattice (nitrogen happily sits inside diamond for example & it would be expected that it would act as a dopant in diamond like carbon as well) 3. The crystal arrangements of carbon that ...

Powerful permanent magnets with easily available materials

#engineering #magnets Magnets are critical to energy infrastructure today. They are used in generators (coal,hydroelectric,wind) ,motors in electric vehicles,mechanical pumps etc. Most magnets today use nickel,cobalt,neodymium, Strontium etc. These materials are hard to find, extract & purify. For a renewable energy future it is extremely important to make magnets from easily available materials. Latest research has shown that permanent magnets can be made from abundant materials : iron,carbon,silicon & nitrogen Iron nitride has already been demonstrated as the most powerful magnet ever synthesized but nitriding can be a little complicated. https://phys.org/news/2010-03-iron-nitrogen-compound-strongest-magnet.html https://magnairon.com/technology/niron-2/ Reasonably powerful magntes can be created with composites of iron,carbon and silicon. These elements are much easier to work with. https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.15.024012 https://www...

Optical properties of carbon allotropes

1. Single atom spectrum If we consider carbon as a single atom then it emits all over the visible light spectrum. There are emission lines in red,yellow,green,blue indigo & violet colors. With carbon there's a complete rainbow of colors. By applying corresponding energies(electrical,heat,mechanical it doesn't really matter what kind of energy)specific color lines would be obtainable in carbon. 2. Graphite vs diamond vs diamond like carbon Practically speaking however we don't really find one atom of carbon floating around displaying its vivid colors. Carbon atoms arrange themselves into a dark black graphitic form or a transparent diamond form. Already we have two extremes of optical properties in a single element. But there's also diamond like carbon. In this form due to functionalization the bond angles of hetero atom-decorated carbon starts to look like that of sp3 diamond. Consequently its properties tend to shift towards diamond as well. It becomes opti...

Which book will help me to make my own wireless network?

Wireless networking is one of those things that is easier to do in practice than it is to learn in theory. You will learn more by jumping in right ahead rather than poring through the books. But if you’re an absolute beginner you need to start somewhere. So I’ll give an overview of the practical aspects of wireless networks first and towards the end of my answer I’ll give suggestions from where you can learn the theory. All wireless networks have three basic components Antennas that send out wireless signals A hardware that provides input signal to the antennas which it sends out wirelessly An operating system that controls the hardware, which sends the input signals to antennas, which then sends it out wirelessly. Now if you look at something as basic as a wifi router you’ll note that it has Antennas (either external or on chip) A chip to which those antennas are connected An OS (that is accessible through the web admin panel) that controls the chip So as a start you should try ...

Notes by Akshat Jiwan Sharma

Search This Blog