Metal doped ZnS nanoparticles are prepared by chemical route. In PL ( Photoluminescence ) measurement excitation wavelength of 300nm and 325nm are used. In PL spectra same peaks but of different absorption intensities were observed.
Dear Bhaskarjyoti,
It is correct to excite your semiconductor samples with radiation of higher energy than their band gap energy. However, it seems you did not put a high-pass filter at the entrance of monochromator to eliminate the laser radiation dispersing from the sample. Once the laser radiation (dispersed by the sample) is eliminated from the emission, you can detect the emissions without problem. As the PL emission of your samples is weaker (than the dispersed laser radiation) you can not detect the emission in your recorded spectra.
The "suitable" is (like Umapada Pal said) when excitation energy is higher than band gap ... but if You want to test it You have to do photoluminescence excitation experiment PLE. In PLE energy of the observation is constant, and You change energy of excitation. Energy of the observation usually is set at PL peak - if You have more PL peaks, just do more PLE spectra for all peaks. You will get info - which excitation is "suitable" for different PL peaks.Try "PLE spectum" and "photoluminescence excitation spectra" in GOOGLE for more detailed info..
In PL ( Photoluminescence ) measurement excitation wavelength of 300nm and 325nm are used. In PL spectra peaks with different(longer) wavelength were observed. ex. the blue emission (430 nm) or orange luminescence (620 nm) or green emission(510 nm) from metal doped ZnS were observed.
Dear Bhaskarjyoti
Please follow these points to find out the suitable excitation wavelength....
1. Record UV spectra of your sample by using any DRS instrument.
2. See the absorption edge.
3. Excite ur sample with that wavelength and record emission spectra.
4. If you don't have DRS instrument better you record first excitation spectra for ur sample by giving the emission wavelength of those color which you are expecting for your sample.
5. the range of excitation wavelength should be 200 nm to 20 nm less than your emission wavelength.
6. Now the last point, check the excitation spectra and find out the highest intense peak. The wavelength belongs to highest intense peak, is the suitable excitation wavelength for ur sample.
Good Luck.
To observe PL spectra of your sample you may follow the steps as pointed out by by Hansnath Tiwari and take the precaution as mentioned by Umapad Pal above. Also take care of the possibilities of quenching effect in your sample.
It is correct to excite your semiconductor samples with radiation of higher energy than their band gap energy. However, it seems you did not put a high-pass filter at the entrance of monochromator to eliminate the laser radiation dispersing from the sample. Once the laser radiation (dispersed by the sample) is eliminated from the emission, you can detect the emissions without problem. As the PL emission of your samples is weaker (than the dispersed laser radiation) you can not detect the emission in your recorded spectra.
Dear sadanand, PL and fluorescenec are just the same but PL is used by physicists and the other is used by chemists.
Dear sir,
the suitable excitation wavelength can get
using the DRS, you record the UV spectra of your sample., the absorption edge, excite your sample to record emission spectra.
you must record the first excitation spectra for ur sample by giving the emission wavelength of those colours which you are expecting for your sample, the range of excitation wavelength is 200 nm to 20 nm less than your emission wavelength.
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