Raman scattering.

Anti Stokes emission means emitted photon has more energy than absorbed photon. The origin of this extra energy can be : (i) two photon absorption (where simmultenously two photons are absorbed to excite a molecule and then it jumps back to ground state as one photon having energy higher than both the protons). (ii)hot band absorption (If absorption occurs from higher vibrational states (hot bands) of ground electronic state and emission is common fluorescence, i.e, from excited state to ground vibtrational level of ground electronic state; then emissive energy is higher. (iii) Upconversion process ( There are many mechanisms of this process. Simple one is absorbed photon receives extra energy from some sensitizer to move to higher excited state and from their emission occurs). There are many interesting notes on anti Stokes shift emission. For organic dyes oit could be hot absorption process or some sort of upconversion process.

This is a beautiful paper regarding this

https://pubs.rsc.org/en/content/articlelanding/2017/cs/c6cs00415f#!divAbstract

Thank you for your response Nilmesh. I have come across and gone through the paper you suggested. Its helpful to understand the possibilities behind antistoke shift but have one doubt if we predict the possibility of hot band absorbance or up-conversion behind anti-stoke ...is this both phenomenon observable in UV-vis spectroscopy and spectrofluorometry (200-800 nm) under normal temperature condition?

secondly, i m getting weak dual emission at 430 & 460 nm where they have suggested hot band absorption based antistoke emission is usually longer wavelength from yellow to red. On the other side, TTA conversions for some molecules has shown emission with antistoke shift in blue region. But have one doubt can we record TTA based emission in regular spectroflourometer at normal Temp condition.

Regards,

Deepali