Dear Prof,

Probably the filter is not a good quality, we have seen the same problem, you can test directly with a laser of 632.8 nm without sample or with another one with low power

Dear Nejeh

thank you for reply. But the filter (a cut off at 500nm) is used to verify that the peak at 600nm is a multiple of a radiation wavelenght.

The problem remains when the wavelenght of the excitation radiation (lambda) is varied. Always a peak appears at 1.5 x lambda.

Dear Kamel

Wich model of spectrometer are you using? Does it work on the first order of diffraction, a single diffraction grating?

Dear Vasil'ev

Thank you for your interest.

I use a Perkin Elmer spectrofluometer LS55.

Best regards

Dear Kamel

Have you already solved the problem?

Dear Vasil'ev

I found an explanation for the LS 55 but I am not convinced because, I encounter the problem with other spectrometers. (when we excite with 400nm, the radiation of 200nm is also transmitted as an excitation radition. The radiation at 600nm is the third order of 200nm)

Please what did you mean by " Does it work on the first order of diffraction, a single diffraction grating"

Most spectrometers use a grating and what you may be measuring are the higher diffraction orders.

The origin of this may be in the excitation, it is necessary to analyze the excitation signal first. Various harmonics can occur as a result of poor excitation signal or measurement signal processing.

Dear Dudic

Thank you but as i saïd in my response of april 11; I encounter this problem when I excite with a laser