# Anionic organic coating raises nanodiamond photoluminescence up to 247 times in lab suspension tests

- Published: 2026-11-14 14:54 UTC
- Section: Machines & Making › Materials science
- Tags: nanodiamond photoluminescence, 247-fold enhancement, nitrogen-vacancy centers, lithium bis(trimethylsilyl)amide, surface functionalization, anionic organic coating, band bending, Discover Sensors, quantum sensing
- URL: https://realtech.media/news/rt-bfe24b1aa737eeb9099793a4_anionic_organic_coating/

**Treatment of 50-nanometer nanodiamonds with lithium amide in hexanes gave a 247-fold emission gain at 637 nm. Low brightness has limited their use in quantum sensing.**

![Anionic organic coating raises nanodiamond photoluminescence up to 247 times in lab suspension tests](https://realtech.media/media/2026/11/8f7f33a4a2fea8f9.jpg)
*Gavin Morley, Wikimedia Commons, CC BY-SA 4.0*

A research team led by Mallory Zapata and Ming Lee Tang reported a wet-chemical surface treatment that raised the photoluminescence of nanodiamonds by up to 247 times under continuous-wave excitation. The study was published in Discover Sensors and is covered by bioengineer.org [1]. When 50-nanometer nanodiamonds suspended in hexanes were combined with 0.2 molar lithium bis(trimethylsilyl)amide, emission at 637 nanometers rose 247-fold under 488-nanometer excitation and 136-fold under 532-nanometer excitation, compared with untreated controls [1]. The authors report that this is the largest increase in nanodiamond brightness documented to date.

## Why nanodiamond brightness matters

Nanodiamonds have an inert crystalline carbon core and a chemically reactive surface that can host nitrogen-vacancy defect centers. These centers exist in positive, neutral and negative charge states. The positive state does not luminesce, while the neutral and negative states do [1]. The negatively charged center can be optically spin-polarized at room temperature with green laser light, which is relevant for quantum sensing and quantum information processing. According to the study, wide practical use has been constrained by the low luminescence of raw nanodiamonds [1].

## Coating method and measurements

The particles were made by high-pressure, high-temperature synthesis with 100–200 ppm of nitrogen and contained both H3 and nitrogen-vacancy centers. They were purified in a sulfuric and nitric acid bath at 90 °C for 10 hours, which left carboxylic acid and hydroxyl groups on the surface [1]. Lithium, sodium and potassium bis(trimethylsilyl)amides were added in a glovebox at minus 78 °C. The base removes protons from surface groups, while enolates formed from side reactions of tetrahydrofuran deposit on the facets and build a negatively charged organic shell [1].

The gain depended on solvent and counterion. In tetrahydrofuran, the lithium base gave 36-fold and 34-fold increases under 488 and 532 nanometers, while the sodium and potassium analogues gave 31-fold and 14-fold. The maximum 247-fold gain came in dry hexanes after an eight-hour reaction. Background from base-solvent controls was subtracted [1].

Transmission electron microscopy showed particles of 50–100 nanometers with a lattice spacing of 2.22 angstroms. Infrared spectroscopy showed the carbonyl stretch shifting from 1770 to 1570 reciprocal centimeters. In dimethyl sulfoxide, the zeta potential went from minus 38 to minus 8.5 millivolts, then settled between minus 15 and minus 23 millivolts, and aggregates of about 1000 nanometers broke up into colloids with a hydrodynamic radius of about 200 nanometers. Kelvin probe and photoemission measurements put the valence band maximum at 3.93 electron volts after treatment, versus 4.58 before, and the Fermi level at 2.80 electron volts, versus 3.65 [1].

## Sources

1. [bioengineer.org](https://bioengineer.org/surface-chemical-coating-boosts-nanodiamond-light-emission-up-to-247-times)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-bfe24b1aa737eeb9099793a4_anionic_organic_coating/