Hello again - Welcome back to LuxeSci, a podcast to re-ignite your wonder by exploring the science behind luxury items. This week we are continuing our birthstone series and talking about rubies, which are the birthstone for July.
Dimos - what is something you wonder about ruby?
Well, i have a small quiz…ruby is one of the four precious gemstones, do you know all of them?
One thing i learned was that may precious gemstones are heat-treated to improve color and clarity (aquamarine to get deeper blues) sapphire and ruby are heated to improve color. Diamond must be protected b/c it is a different mineral species, essentially carbon and can turn black and scorch in high heat.
Alexis - I was wondering what biomedical applications they could have since we’ve learned alot about diamonds and sapphires and emeralds and how they are used in nanotechnology.
Now I have a brother who has a July birthday and he’s not really a jewelry person anyway but he definitely wasn’t gettin any ruby jewelry anyway since rubies are pretty pricey. I think I said this in our episode on garnets, that I have always liked the dark red of garnets more than rubies but I’m coming around to the more pinkish color of rubies. Interestingly, rubies are often confused with spinels though they are different minerals
Dimos - what are your experiences with rubies?
Background:
Rubies are part of the corundrum mineral family (along with sapphires), which means they are composed primarily of aluminum oxide (by contrast, spinel contains magnesium as well as aluminum)
Their red color is caused by chromium impurities in the crystal, this also causes fluroescence
They have the highest per carat cost of any gemstone
Fun fact - there is a minimum color saturation that must be met for a stone to be called a ruby here in the US, otherwise it’s a pink sapphire, whereas international gemological societies have widen the definition of a ruby to include the paler pink varieties
The most valuable rubies are from Myanmar, the Himalayas and Northern Vietnam and are formed in marble
Fun fact - marble is formed when heat and pressure act on limestone deposits
Marble has a low iron content so the rubies formed in marble have a low iron content and an intense red color.
They also fluoresce red in ultraviolet light (including sunlight) as so appear even more intensely red
Rubies can also form in basalt, which can have higher iron content making them darker red and less intense
Now some of the history
The word ruby comes from the Latin ruber or red
Rubies are mentioned 4 times in the bible in association with beauty and wisdom
The Sanskrit word for rubies is ratnaraj or “king of stones”
The earliest recorded occurrence of ruby trade is on the Northern Silk Road. In 200 BC rubies were recorded as part of the trade West from China
In Burma (Myanmar), warriors carried rubies to make them invincible in battle, but it wasn’t enough to wear the rubies, they inserted them into their flesh and made them part of their bodies
Science:
Dimos: Industrial Uses (https://www.materialshub.com/material/ruby/)
In 1837, Marc Antoine Gaudin made the first synthetic rubies by fusing alumina at a high temperature with a small amount of chromium as a pigment. Next to the diamond, the ruby is the hardest gemstone; it is also resistant to acids and other harmful substances. Because large, gem-quality rubies are so rare, the value of a fine ruby may be quadruple that of a similar-quality diamond. Natural rubies are found in a handful of sites around the world, such as Myanmar, Thailand, Sri Lanka, Afghanistan, Tanganyika, and North Carolina.
Rubies and sapphires are both composed of corundum, which is the crystalline form of aluminum oxide. They differ only in small amounts of chromium that gives rubies their characteristic red colour, with higher concentrations producing darker shades.
In addition to their decorative functions, rubies serve a broad range of practical purposes. For example, because of their hardness, they make long-lasting thread guides for textile machines. Ruby is even harder than steel, so it is an excellent bearing material for metal shafts in devices such as watches, compasses, and electric meters. Rubies have an exceptional wave-transmitting property that makes them ideal for use in lasers and masers. These are laser-like devices that operate in non-visible ranges of microwaves and radio waves.
Because many of these industrial uses demand very high-quality crystals of particular sizes and shapes, synthetic rubies are manufactured. With the exception of minor amounts of impurities, synthetic gems have the same chemical, physical, and optical properties as their natural ones. Although some are used as gemstones, about 75% of modern synthetic ruby production is used for industrial purposes.
Ruby Lasers were some of the first lasers ever created but they are not as popular anymore due to their low efficiency. However they were the first ever useful lasers and their invention paved the way for many other lasers.
In early demonstrations the pulses of red light were not only coherent (visible to the naked eye) but also powerful enough to pop red balloons (though not blue balloons) as the power of the laser was absorbed by the color of the balloon. Some existing uses include medical treatments, tattoo removal, and high power applications where the target of the laser is perfectly matched to the wavelength of the ruby laser, specifically applications like drilling holes into diamond.
Encyclopedia Britannica States:
The laser is based on the principle of stimulated emission proposed by Albert Einstein in 1917. When atoms have been induced into an excited energy state, they can amplify radiation at a frequency particular to the element or molecule used as the laser medium
Laser emission is shaped by the rules of quantum mechanics, which limit atoms and molecules to having discrete amounts of stored energy that depend on the nature of the atom or molecule. The lowest energy level for an individual atom occurs when its electrons are all in the nearest possible orbits to its nucleus (see electronic configuration). This condition is called the ground state. When one or more of an atom’s electrons have absorbed energy, they can move to outer orbits, and the atom is then referred to as being “excited.” Excited states are generally not stable; as electrons drop back to their original state they release energy in the form of a photon. This packet of energy is manifest as a flash of light.
The inventor the Ruby laser: Maiman was born in Los Angeles in 1927. At a young age his family moved to Denver, Colorado, where he helped his father with experimentation in a home electronics laboratory. Maiman says in his autobiography that "as with most hyperactive kids, I was skinny, some 10–15 pounds underweight", and considers himself to have been a target for Ritalin should it have existed at the time.[15] In his teens Maiman earned money by repairing electric appliances and radios,[16] and after leaving high school was employed as a junior engineer with the National Union Radio Company at age 17.[17]
Following a year's service in the United States Navy at the end of World War II,[18] he earned a B.S. in engineering physics from the University of Colorado Boulder. Maiman then went on to graduate studies at Stanford University where he earned an M.S. in electrical engineering in 1951 and a Ph.D. in physics in 1955.
Maiman's doctoral thesis in experimental physics, under the direction of physicist Willis Lamb,[10] involved detailed microwave-optical measurements of fine structural splittings in excited helium atoms. He also devised laboratory instrumentation for Lamb's experiments. Maiman published two articles jointly with Lamb in Physical Review, the second of which was based on his own thesis research.[19][20] His thesis experiment was instrumental in his development of the laser.
Alexis: Biomedical Uses
Now for something a little different, but still playing off the optical properties of rubies.
I’m sure everyone knows someone who has had radiation therapy for cancer. One of the challenges of radiation therapy is knowing that you’re giving the dosage you want to give the patient, right at the site of the tumor
Rubies are being investigated as inorganic scintillation detectors for measuring the quality of radiation therapy in vivo
Scintillation detectors - a scintillator is a material that luminesces when excited by ionizing radiation so a scintillation detector detects that luminescence. It’s a way to measure radiation. Usually it’s the scintillation material and a photodetector that coverts the light of the luminescence into an electrical signal
Gustavo Kertzscher and Sam Beddar published an article in Physiology Medicine and Biology journal in 2017 looking at rubies to detect the quality of radiotherapy in brachytherapy dosimetry.
This is radiation therapy that is put inside your body
Dosimetry - determination or measurement of the amount of radiation exposure
Back to the paper, the authors argue that these inorganic scintillation detectors have several advantages, including that they are small and can be put into the BT catheters into the tumor region (thus measuring the radiation at the target) and energy and temperature dependencies can be easily corrected for
Additionally, these type of scintillation detectors emit in the red wavelength regions
This allows for the removal of the Cerenkov and fluorescence effects (removal of unwanted Cerenkov and fluorescence light produced in the fiber optic cable that links the detector volume with the photodetection system)
There are also a wide variety of materials that can produce scintillation intensities much larger than their organic counterparts
Allows for the measurement of much smaller doses
Rubies are especially good inorganic scintillation materials as they have a narrow emission spectrum near 694nm (red!) and this overlaps less with the Cerenkov and fluorescence interference we just mentioned
Although the inorganic materials are better a detecting low doses, the authors of this paper wanted to see if rubies could be used for high-dose-rate dosimetry and compared them to plastic scintillation detectors
They found that the rubies introduced some error due to their own luminescent properties but that using a filter between the ruby crystal and the fiber optic cable could suppress that photoluminescence.
In summary - using rubies could allow for very precise dosimetry and quality control of in-vivo radiation therapy.
Remember how I said earlier that it’s relatively easy to confuse ruby and spinel?
The authors of a 2019 paper in Scientific Reports (Andre Jacques Batista et al) came up with a way to etch a QR code on a stone as a way of authentication
They used natural diamond, synthetic ruby and synthetic sapphire using femtosecond laser writing to etch a micro QR code onto the stones
Femtosecond laser - infrared laser with a wavelength of 1053 nm
Emits bursts of energy at a very fast rate (femtoseconds)
Introduced in the US in the 1990s
Used in eye surgery - such as LASIK
The authors were successful in etching micro dots onto the stones, which they verified by optical and electron microscopy
This could allow the jewelry industry to micro-encrypt stones without the current paper trail and without the need to remove the stone from the setting to authenticate it.
Finally, for something interesting, at least for us nerds:
I found a paper fro 1928 by EL Nichols and HL Hows at Cornell University published in the Protocols of the National Academy of Sciences
Investigation of the luminescence of rubies under cathode and photo-excitation
They found that, among other observations:
The activator is chromium in solid solution with aluminum oxide
Al2O3 is very sensitive to activation by chromium - it was hard to produce aluminum oxide that did not glow red (ruddy) when subjected to cathode-bombardement
Strictly pure Al2O3 did not glow
So it may be the first published report of chromium’s impact on ruby color and their luminescent properties
Glossary
Scintillation detectors - a device to detect radiation based on luminescence
Brachytherapy - radiation therapy in vivo
Dosimetry - determination or measurement of the amount of radiation exposure
Femtosecond laser - infrared laser used primarily in eye surgery
Cocktail party facts
What makes rubies red?
What’s the difference between a ruby and a pink sapphire?
What’s the connection between rubies and LASIK eye surgery?
Whelp, you’ve spent another 20 minutes with us and we hope you feel a little smarter for it. Thank you for going on this journey of discovery with us about all things ruby. We hope you remember a little fact about rubies the next time you see one, or someone mentions their LASIK surgery.
THank you for listening to this episode of LuxeSci. A very special thanks to my audio engineer and co-host Dimos. OUr theme music is Harlequin Mood by Birdie. We’re all over social media at LuxeSci Pod and we’ve recently started a Youtube channel, you guessed it: LuxeSci Pod. You can listen to our episode there and we’re going to start making some additional content for the site in the next month of so. You’re going to want to tune into that and our Instagram page in September as we start chronicling our year spent in Greece. Exciting!, you’ll get a mash-up of expat fun, history and of course, luxurious science.
Lastly, don’t forget to tell 2 people about the podcast. Referrals is how we grow.
Music: Harlequin Mood by Burdy
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