A new class of diamond flaws has been identified by researchers from Skoltech, Moscow Pedagogical State University, and other academic institutions. These defects may be useful for quantum information processing and accurate and distant temperature monitoring inside very small things, such as living cells. The findings are reported in a letter published in Physical Review B.
The phrase “color centers” is used to describe a variety of flaws in transparent crystals, most often diamonds. A color center is typically an extraterrestrial atom, like nitrogen, inserted into the diamond crystal lattice with one or more neighboring carbon atoms missing.
What gives color centers their name are their optical properties. Diamond is transparent to visible light overall, but color centers spots inside it have the intriguing technological ability to absorb light and effectively re-emit it in a relatively limited spectral range, that is, with a very specific color (wavelength).
Importantly, color centers can effectively emit single photons. Where this narrow-band single-photon emission comes in handy several potential applications.
Single photons are building blocks for quantum optics and quantum information applications. For example, such photons are useful for the ultimate data security technology quantum encryption. It involves the exchange of keys for and encrypted communications that enable secure information transmission between two parties.
A secure channel must be used to transmit the key, and some quantum key distribution algorithms call on a reliable source of single, undetectable photons. It implies that the polarization and wavelength of the emitted photons, among other characteristics, must precisely agree.
The wavelength of the light emitted from color centers has another intriguing characteristic in that it is temperature-sensitive. As a result, photons generated by these flaws contain information about the environment’s temperature where the diamond is located.
The ability to make nanodiamonds with integrated color centers allows for the development of tiny thermometers with great spatial and temperature resolution. Such temperature sensing, according to the researchers, would be useful in biological applications. Nanodiamonds have already been inserted into cells in prior experiments to look at internal temperature fluctuations.
We did not introduce any defects on purpose, and yet the color centers reported in our study presented themselves with only slight variations in pure synthetic microdiamonds from three different batches. The microdiamonds were produced via high-pressure, high-temperature synthesis with the use of an organic compound called adamantane as precursor. It remains to be determined whether these color centers also come up in natural diamonds and in synthetic ones produced by other methods.
Neliubov
“Color centers in diamond have been known and studied for about 40 years. The new variety that we discovered has superior properties as far as potential technological applications go. Namely, the spectral range of emission from our centers is almost 10 times narrower compared with all previously known color centers. The narrow-band emission and the high brightness would make for more sensitive thermometers,” the lead author of the study, Skoltech Ph.D. student Arthur Neliubov, commented.
He added that a further interesting property of the new color centers is narrow-band excitation: They not only emit light in a narrow spectral band, but absorb it selectively as well. Every color center, even those in the same class, differs somewhat in certain ways, and there are applications where this might be used to very specifically elicit a response from them.
The “defective” microdiamonds may be useful as nontoxic, nonradioactive, and highly distinctive biomarkers in multicolor imaging, a biological analytical approach.
The fluorescence spectra graphs, which describe the light emitted by the diamond sample, have so far been used to identify the new color centers. However, the actual nature of these defect centers is yet unknown. The researchers have a couple of guesses but say more research is needed.
“We did not introduce any defects on purpose, and yet the color centers reported in our study presented themselves with only slight variations in pure synthetic microdiamonds from three different batches,” Neliubov said.
“The microdiamonds were produced via high-pressure, high-temperature synthesis with the use of an organic compound called adamantane as precursor. It remains to be determined whether these color centers also come up in natural diamonds and in synthetic ones produced by other methods.”
The team also intends to study the optical properties of the newly discovered color centers at very low temperatures in the future. In fact, this could reveal the nature of the physical flaw in the crystal lattice that lies beneath the color center.
The discovery, according to the scientists, was made possible by the creation of a revolutionary methodology. The researchers managed to combine two different experimental techniques: scanning electron microscopy and fluorescence spectroscopy.
“This enabled us to label the most interesting microdiamonds exhibiting color centers and conduct multiple series of experiments on the same diamonds using different equipment. Also, the high sensitivity of the experimental setup allowed us to zoom in the analysis to the point where we were looking at individual color centers. That’s how we could characterize this new class of emitters,” Neliubov explained.
