UV-visible spectrophotometric measurement of material absorption and transmission spectra - Database & Sql Blog Articles

UV-visible spectrophotometric measurement of material absorption and transmission spectra

UV-visible spectrophotometric measurement of material absorption and transmission spectra

Key words: transmission spectrum; ultraviolet-visible spectrophotometry; US-analytical instrument ; uv-1100

First, the purpose of the experiment
a) Understand and master the principle, structure and use of UV-Vis spectrophotometer
b) Characterization methods for absorption, transmission and reflection spectra of substances
c) Principle and method for measuring semiconductor forbidden band width by ultraviolet-visible spectrophotometer

Experimental principle:
d) The basic working principle of the UV-Vis spectrophotometer is that when a certain frequency of ultraviolet-visible light illuminates a substance, electrons transition between different energy levels to selectively absorb the excitation light. The spectrum that varies with wavelength reflects the characteristics of the sample. Measuring spectra allows qualitative and quantitative analysis of materials. The UV-Vis spectrophotometer consists of a light source, a monochromator, a sample holder, a detector, and a computer data acquisition and processing system. Based on the transmission and reflection spectra of the measured materials, the absorption properties of the materials for ultraviolet-visible light are obtained, thereby conducting material detection, research and development. It can analyze a wide range of materials, whether transparent, non-transparent, block, film or powder.
e) The forbidden band width Eg of a semiconductor or insulator material can be tested using an ultraviolet-visible spectrophotometer. When the photon energy is close to the bandgap width of the material, the loss is controlled by the intrinsic absorption of the material, the absorption coefficient, the film sample thickness and the transmittance (T) are satisfied:

Above the intrinsic absorption, the relationship between the absorption coefficient and the incident photon energy can be expressed as

Second, experimental data processing
a) The band gap is measured by the transmission spectrum of Cu2O film
i. Raw data:

Ii. Curve image

Iii. Get the intercept Eg

After drawing and fitting the curve, Eg = 3.0596 ev is obtained, which is in good agreement with the expected value.

b) The forbidden band width is obtained from the reflection spectrum of TiO2 powder
i. Raw data:

Iii. Get the intercept:

After drawing and fitting the curve, Eg=3.0404 ev is obtained, which is in good agreement with the expected value.
c) Selected as an experiment: The concentration of the MB (methylene blue) solution was tested using UV3010.
It can be introduced by Lambert-Beer's law, lg T=K*C*L , A=K*C*L, K—substance absorption coefficient, unit (1/gcm), C—solution concentration, A—absorbance, the unit is Ab , L—the optical path of the solution (the thickness of the cuvette). From the above formula, the absorbance A is a single-valued (linear) function of the concentration C for a certain optical path L and any (K-constant) light-absorbing substance. The test for C is directly attributable to the test for A.
In the experiment, using deionized water as a substrate, an absorption curve mb1 of a reference solution of 10 mg/L of MB (methylene blue) solution was measured. And the absorption curve of the unknown concentration solution mb2 was measured. Read the absorbance Abs at the absorption peak to find Cx

Peak value of 10mg/L standard solution:

Sample sample Sample_1 peak value:

Therefore, the concentration of the sample 1 solution is: mg/L

Sample sample Sample_2 sample peak:

Therefore, the concentration of the sample 1 solution is: mg / L
III. Experimental Conclusions Through this experiment, we have learned the basic use of the UV-Vis spectrophotometer. By measuring the transmission spectrum or reflection spectrum of the material, the absorption information of the material for UV-visible light is obtained, and the corresponding forbidden band width Eg is calculated. In the selected experiment, by measuring the absorbance Abs curve of the solution, according to Lambert-Beer's law, the concentration of the solution is only proportional to the absorbance under certain conditions, and the absorbance value at the peak of the selection curve can be converted into relative Solution concentration value. However, the method is mainly used for the colored solution. For the colorless solution, for the colorless solution, an appropriate color developing agent can be selected according to the composition of the solution, and the color depth and concentration of the solution after the coloring agent is required to be added can be continued. measuring.

Key words: transmission spectrum; ultraviolet-visible spectrophotometry; US-analytical instrument ; uv-1100

Ii. Curve image: