Raman Spectroscopy is an excellent method to characterize carbon nanomaterials. Its fairly complex so I am going to try to explain this in a very simple language. The ratio of intensity of D/G bands is a measure of the defects present on graphene structure. The G band is a result of in-plane vibrations of SP2 bonded carbon atoms whereas the D band is due to out of plane vibrations attributed to the presence of structural defects. Now, when you compare the spectra of graphene and graphene oxide, GO will have a higher D band. This is due to the disruption of SP2 bonds of the carbon as GO has oxidative functional groups. 

So, if the D band is higher, it means that the SP2 bonds are broken which in turn means that there are more SP3 bonds. However, D band can be present due to various other reasons. So if your D/G ratio is higher than pristine graphene, it means that there are defects. It does not mean that you have more SP3 than SP2 in the same sample. It shows that you have more SP3 in GO compared to pristine graphene.

You can also try high resolution XPS which can give you elemental quantification and see what functional groups are present.

The limitation of Raman and XPS both is that these are point - surface - techniques. This means that you are only measuring a very small region of the entire sample, precisely a point that is on the surface. However, this is an accepted limitation of these techniques and therefore I would be very careful before drawing any firm conclusions. Its better to do two types of chemical characterization than just doing one. That way you can be more sure of your data.

We have described this in these articles:

1. https://www.researchgate.net/publication/235619062_Two-Dimensional_Nanostructure-Reinforced_Biodegradable_Polymeric_Nanocomposites_for_Bone_Tissue_Engineering?ev=prf_pub

2.. https://www.researchgate.net/publication/261183815_The_effects_of_graphene_nanostructures_on_mesenchymal_stem_cells?ev=prf_pub 

3. https://www.researchgate.net/publication/264315709_Enzymatic_Degradation_of_Oxidized_and_Reduced_Graphene_Nanoribbons_by_Lignin_Peroxidase?ev=prf_pub

Article Two-Dimensional Nanostructure-Reinforced Biodegradable Polym...

Article The Effects of Graphene Nanostructures on Mesenchymal Stem Cells

Article Enzymatic Degradation of Oxidized and Reduced Graphene Nanor...

very thanks dear lalwani

Gaurav gave a great explanation.

The paper of Ferrari and Robertson is one of the pioneering works on this (below).

http://rsta.royalsocietypublishing.org/content/362/1824/2477.abstract

 thanks Dr. Punckt.

Graphite, Graphene, graphene oxide (SP2 CO double bond or SP3 C-OH bonding ) Diamond, XPS Binding energies can confirm the chemical states.

XPS: Quantitative analysis of sp3 and sp2 contents in the graphene deposited films.

Raman spectroscopy: Qualitative analysis of sp3 and sp2 contents.in the grpahene deposited films.

You can combine XPS results and Raman IG/ID ration to confirm graphene, diamond like, or SP2 CO double bond or SP3 C-OH bonding or more information.

i measure ramen of GO D band is 1353 and G band is 1590

FGO D band became 1343 and G band 1593.6

FG-Ag  D band became 1354 and G band is 1592.6

why  D band and G band   of FG-Ag  became more than D band and G band of GO  ?

why intensity ratio (ID/IG) of reduced graphene oxide higher than the intensity ratio of graphene oxide?

Gaurav Lalwani Thanks for your information about raman spectroscopy for graphene and graphene oxide

In my recent paper I have compared Raman spectra of single layer graphene and single layer graphene oxide with different oxygen content. It will help you.

http://onlinelibrary.wiley.com/doi/10.1002/adma.201503444/abstract

Article Temporospatial Control of Graphene Wettability

This link is really useful,

http://www.instanano.com/characterization/experimental/raman-graphene/

Thanks to all for such informative discussion.

can we apply same logic for Raman spectra of graphene quantum dots ?

Number of discussions are available on change of Y axis value (Id/Ig). What is the significance of shift of D and G band positions at x axis?