if you need the crystal RI then look at the SDS wikipedia entry they give 1.461 but I cant find in the references where they get this value

What information do you want? the Raman spectrum gives the spectrum of Raman active vibrational bands in the material. If there are Raman active impurities, you may see these also. It is difficult to get absolute quantitative information though, and not trivial to get relative quantitative information with a powder sample.

Hi Hugh J Byrne!

Can we get from RS spectra, for exaple, relative concentrations of components, distribution of these?

Thanks

In principle yes, but you probably need to calibrate to some extent. Different components can have different Raman scattering efficiencies, and so some prior quantitative knowledge of the strength is required if you want absolute values. But relative differences are reliable.

 Hug J Byrne, how scaterring effiency depends on differrent components? (In case of nanodiamond, probably there are diamond, graphite carbon, different impurities like hydrogen, bor, nitrogen...

We regisrted on 5 dots of sample and get different spectra?  Need to recall, the sample is heterogeneous.

Thanks

The Raman scattering cross section depends on the polarisability of the individual bonds. Thus, electron rich materials such as conjugated organics (eg Graphene) have much stronger Raman signals that saturated organics (eg diamond).

So if i got peak characterized for graphite and peak characterized for Dia, can i got relative concentration of these components in the sample?

Thanks

Dear Binh Nguyen

You mentioned that detonation nanodiamond (DND) powder is a heterogeneous material. From the fact that you have different spectra from 5 different spots I can conclude that you are working with raw unpurified DND.  {Characteristic size of primary particles of DND is on nanometer scale, right? So, taking into account that you are collecting signal from much bigger spot (at least several hundred nanometers in diameter), purified DND should give same spectra from different spots. It’s not your case}

Raw DND powder can have high and variable levels of heterogeneity (please, correct me if I am wrong).  Higher heterogeneity - more Raman spectra should be collected to estimate “concentration”.  Heterogeneity scale length can be directly obtained by Raman, but it may require Raman mapping with many hundreds if not thousands of single spectra. Time consuming procedure.

Here I propose the simple procedure to get relative “concentration” of components in the heterogeneous sample.

Collect several tenth of Raman spectra (try 10x10 map to collect 100 Raman spectra; use spacing consistent with distances between those 5 spots with different spectra).

Do clustering analysis (PCA may work). If you have two main components, two main clusters will be revealed.  

Number of Raman spectra within the clusters gives you relative “concentration” of the components. Assign clusters (you can add spectra of “pure” known components in to data set and use them as a reference) and count spectra.

If clustering is not prominent, extend data set by collecting extra spectra and repeating clustering.

This approach will give fast estimation of the requested “concentration”.  In addition, you will assess how many components (clusters) you have and level of spectral heterogeneity.

Potential complications with clustering: you may have two clusters but bridged by spectra of spots composed of both constituents; more clusters than you expected – impurities or constituents; some spectra scattered around main clusters; not very clear clustering. But, most probably, you will be able to define boundaries of the clusters and count spectra.

Such preliminary results will guide you what to do next.

Term “Concentration” is usually used for homogeneous samples.

:)     I have Master degree from your university (Faculty of Physics, Department of Biophysics). Will be glad to help

Dear Vitali

Thank you for your mention.

We've already known from X-ray spectroscopy analysis there are 2 phases in our sample: Dia as core of particle and like-graphite as cover. But from RS we got different intensity of peaks in different recording spots with different intensity of luminecsence. So as you mentioned we can product measurement at sevarel tenth of spots, then take the mean value. In that way we can get the "wright" relative concentration of 2 phase in DND?

Thanks :)

I was talking about slightly more complex statistics, but mean spectrum is also can be used. If you have reference spectra of two phase, you can represent mean spectrum as a sum of two reference spectra. Coefficients will give relative contribution. Check Raman cross-sections of your phases. Keep in mind, Raman spectroscopy can expose more complex picture than just mixture of two phases (even from ideal single crystal you may obtain different spectra for different orientations/polarizations).

Hi, Vitali

Do you know where is enable reference spectra of determined phase ? I dont have any.

I would recommend to collect reference spectra by yourself using absolutely the same settings you use for the actual experiment. Just record spectra of pure phases.

If you do not have such samples, it is a more challenging problem. You did not mentioned if you have heterogeneity on the nanometer level. I assume you have it and nano diamond material is usually surrounded by second phase. However, you may have areas with no diamonds. Record it for the first reference spectrum. The second reference spectrum can be obtained by recording Raman spectrum from the area populated with diamonds – let’s call it “mixture spectrum”.  Subtract contribution of the first phase from the mixture spectrum and use resulted spectrum as a reference.  Try different coefficients while subtracting. Estimate percentage of diamond material under laser beam and normalize the second reference spectrum pretending you have pure diamond.  

Check literature. At least diamond spectra should be published.  Call authors for the reference spectrum of nano diamonds. In any case, I would recommend to record the other reference spectrum (not a diamond) by yourself, as it may depend on your production procedure.

Use Multivariate Curve Resolution (MCR) methods to mathematically extract reference spectra from set of mixed spectra

Double check my first answer. In that procedure you don’t need reference spectra at all.