ZnO is an interesting wide direct band gap Ⅱ-Ⅵ semiconductor with wurtzite structure.The high quality ZnO thin film is one of most potential membranous materials at present.Zinc oxide with high stability and a direct band gap of 3.37 eV has attracted tremendous attention because of its high potential for application as short wavelength optical devices.In recent studies

it is found that doping of other elements can broad the band gap of ZnO films.This will be beneficial to the development of optical devices.There are many methods to prepare ZnO films

such as pulsed laser deposition

reactive thermal evaporation

reactive magnetron sputtering

electrodeposition

sol-gel and so on.Sol-gel method has many advantages

may prepare big area semiconductor thin film

fit for industry production

and so on.In order to prepare ultraviolet optical device

study on how to broad the band gap of ZnO is very important.In this paper

in order to study the effect of Mg concentration and annealing temperature on the microstructure and band gap of Zn

1-x

Mg

x

O films

the Zn

1-x

Mg

x

O(

x

=0.1

0.2

0.3

0.4

0.5

0.6

0.7)thin films were prepared on glass substrate by the method of sol-gel.The grown films were characterized by means of X-ray diffraction

photoluminescence spectroscopy and transmission spectrum.The XRD results show that when the value of x is between 0.1 and 0.3

the thin film remains the structure of hexagonal wurtzite and the angle of diffraction peak becomes bigger with increasing x

MgO impurity phase segregated at

x

≥0.4.According to PL spectra

the thin films show an intensive UV emission peak due to the near band-edge emission and a weak UV emission peak around 403 nm between 340 nm and 520 nm at room temperature

and the intensive UV emission peak have the blue shift with the content of Mg increasing from 0.1 to 0.3.It indicates that the band gap of ZnO was broaden with increasing Mg-doping concentration from 0.1 to 0.3.According to the transmission spectrum of Zn

1-x

Mg

x

O(

x

=0.3

0.4

0.5

0.6

0.7)films

it is found that absorption edges are formed when incident wavelength λ

<

350 nm and blue shifted with increase in Mg content.It also indicates more doping Mg may broad the band gap of Zn

1-x

Mg

x

O.Meantime

annealing temperature also can broad the band gap obviously

but the band gap decreases when annealing temperature is above 590℃.Though the doping of Mg can broad the band gap

but high Mg doping can result in precipitation of MgO.Therefore

we must control Mg content and annealing temperature strictly when an optical device is prepared.