Determine The Properties Of Fluorescent Diamond Particles Using Spectroscopy.

Introduce

Fluorescent diamonds are a unique type of diamond. These particles contain color centers—crystallographic defects that emit light when exposed to UV rays, providing insights into the diamond's structure and properties. Spectroscopy is a modern and reliable method for analyzing the properties of fluorescent diamonds. Advances in this area have led to the creation of fluorescent nanodiamonds with vibrant colors, enhancing their utility in scientific and industrial applications.

Understanding fluorescent diamond

Figure 1: Fluorescent diamonds with different degrees of fluorescence.

Fluorescent diamonds are characterized by their ability to emit visible light when exposed to ultraviolet (UV) light. This phenomenon, known as fluorescence, is caused by the presence of trace impurities within the diamond's crystal structure.

Key properties of fluorescent diamonds:

• Fluorescence color: The color of the emitted light can vary widely, ranging from yellow, orange, and pink to blue, green, and even white.
• Fluorescence intensity: The brightness of the fluorescence can vary depending on the concentration and type of impurities.
• Excitation wavelength: The wavelength of UV light that causes the diamond to fluoresce.
• Decay time: The time it takes for the fluorescence to fade after the UV light source is removed.
• Temperature dependence: The intensity and color of fluorescence can be influenced by temperature.

Factors affecting fluorescence properties:

• Impurity type and concentration: The type and concentration of impurities within the diamond determine the fluorescence color and intensity.
• Diamond crystal structure: The crystal structure of the diamond can affect the way light interacts with the impurities, influencing the fluorescence properties.
• Treatment history: Diamonds may undergo treatments like irradiation or heating, which can alter their fluorescence characteristics.

Method

Spectroscopy is a powerful tool for analyzing the properties of fluorescent diamonds. By studying the interaction of light with the diamond, researchers can gain insights into its composition, fluorescence characteristics, and other relevant parameters. Here are some of the most used spectroscopic techniques:

Photoluminescence Spectroscopy (PL)

• Principle: PL measures the light emitted by a diamond when excited by a light source (e.g., UV laser).
• Information: PL spectra provide information about the energy levels of impurities within the diamond, which determine the fluorescence color and intensity.
• Applications: Identifying the type of impurities responsible for fluorescence, quantifying the concentration of impurities, and studying the effects of different treatments on fluorescence.

Raman Spectroscopy

• Principle: Raman spectroscopy measures the vibrational energy of molecules within the diamond lattice.
• Information: Raman spectra can reveal the presence of specific impurities and provide information about the diamond's crystal structure.
• Applications: Distinguishing between natural and synthetic diamonds, identifying treatments such as laser irradiation, and studying the effects of strain on the diamond lattice.

UV-Visible Spectroscopy

• Principle: UV-Vis spectroscopy measures the absorption of light in the ultraviolet and visible regions of the spectrum.
• Information: UV-Vis spectra can provide information about the presence of color centers and other defects within the diamond.
• Applications: Identifying the cause of color in colored diamonds, studying the effects of radiation on diamond properties.

Result

Figure 2 examines how different UV wavelengths affect the color and brightness of diamond fluorescence. It shows that the diamond's color can change from greenish yellow to yellowish green with orange-red hues depending on the UV light used (365 nm vs. 405 nm). Additionally, the brightness of the fluorescence can vary, with blue fluorescence being more intense under 405 nm UV light compared to 365 nm.

Figure 2: Two different samples of fluorescent diamonds are projected by different UV wavelengths that emit different colored light.

From that result, we can analyze properties such as:

• Fluorescence Color: The figure shows how different excitation energies (365 nm and 405 nm) affect the color of fluorescence in diamonds.
• Fluorescence Intensity: It compares the intensity of fluorescence under different excitation wavelengths, highlighting variations in emission peaks.
• Emission Peaks: The figure illustrates the specific wavelengths at which fluorescence peaks occur for different excitation sources.
• Impact of UV lamp emissions: It demonstrates how the mixture of emissions from a conventional UV lamp can influence the observed fluorescence color and intensity.

This demonstrates the importance of using consistent UV sources for reliable fluorescence observations.

Measurement system

The Ocean Insight FLAME UV-Vis spectrometer is a versatile instrument designed for a wide range of applications, including the analysis of the fluorescence properties of diamonds. It offers a wavelength range of 190-1100 nm, allowing for detailed examination of materials across the ultraviolet, visible, and near-infrared spectra. With an optical resolution that can be as fine as 0.1 nm (FWHM), it provides precise measurements essential for characterizing fluorescent materials. The spectrometer's electrical performance is robust, featuring a signal-to-noise ratio of 250:1 for single acquisition and a dynamic range of 1300:1, also for single acquisition. This ensures clear and accurate data collection even for subtle fluorescence signals. Additionally, the FLAME spectrometer is known for its thermal stability, with a drift of only 0.02 nm/°C at the 650 nm range, which is crucial for consistent results during temperature fluctuations. The integration time is flexible, ranging from 1 ms to 65 seconds, accommodating both fast and slow-changing phenomena. For ease of use and quick data transfer, the spectrometer connects via USB. The compact and user-friendly design of the FLAME UV-Vis spectrometer, combined with its technical capabilities, makes it an excellent choice for analyzing the complex properties of fluorescence in diamonds and other materials.

Figure 3: Ocean Insight FLAME spectromerter.

The Ocean Insight LDC-1C LED Controller is a compact, single-channel driver designed for seamless operation with LED Light Source Modules (LSMs). It features a user-friendly, menu-driven interface and a touchscreen for easy programming and waveform display. The controller can read operational information from the LSM, ensuring protection against excessive current and enabling various modulation modes for precise control. The LSMs offer a range of discrete wavelengths from 265 nm to 880 nm, suitable for fluorescence excitation in applications such as diamond analysis. These wavelengths include UV, visible, and NIR options, providing versatility for different fluorescence properties analysis. This setup is ideal for analyzing the fluorescence properties of diamonds, as LED light sources can provide narrow, well-defined UV emissions for more reliable observations.