ZnO-based luminescent nanomaterials have attracted comprehensive attention because of their great potential applications in ultraviolet laser devices

LED fabrication and bio-imaging due to their large exciton banding energy (60 meV) and wide bandgap (3.37 eV)

low toxicity and high photo-stability. ZnO nanomaterials exhibit two kinds of emission: one is ultraviolet (UV) near-band-edge emission at approximately 380 nm and the other is visible deep-level emission in the range 450~730 nm. Generally

ZnO nanomaterials fabricated at high temperature by PLD

CVD and magnetron sputtering get good crystallization and exhibit near-band-edge emission with negligible visible emission. To get highly luminescent visible light emitting ZnO nanomaterials

mass of visible light emitting defects should be introduced to ZnO crystal. Low temperature fabricating and doping are two kinds of methods to introduce defects into crystals.Because the tetrahedral ionic radius of Mg

2+

(0.057 nm) is similar to that of Zn

2+

(0.060 nm)

wide range solubility of Mg

2+

in the zinc blend structure is expected. So

Mg

2+

doped ZnO nanomaterials have been studied comprehensively. At high temperature

Mg

2+

ions take Zn

2+

positions in hexagonal structure and form Zn

1-

x

Mg

<

em

>

xO alloys

band gap of which can be tuned in 3.3~7.8 eV by verifying Mg

2+

content. The alloys have been used widely in ultraviolet lasers and Zn

1-

x

Mg

<

em

>

xO/ZnO heterojunction optoelectronic devices research. However

at low temperature in liquid

because of low free energy and short ionic radius

Mg

2+

ions can facilely enter interstitial positions between lattice planes of wurtzite structured ZnO and form Zn vacancies in the crystal

which should introduce energy levels in band gap of ZnO and make the ZnO nanomaterials emit strong visible light. So

it is of both theoretical and practical meanings to study luminescent property of Mg doped ZnO namomaterials prepared at low temperature.In typical preparation

ZnO colloidal nanocrystals were synthesized at 50 ℃ by dropwise adding 10 mL of tetramethylammonium hydroxide 0.552 mol/L in ethanol(AR) dropwise into 30 mL solution of zinc acetate 0.101 mol/L(C

4

H

6

O

4

Zn2H

2

O) (AR) in DMSO(AR) under constant stirring. When doping with Mg

2+

we added 10 mL of tetramethylammonium hydroxide 0.552 M into 30 mL solution of zinc acetate and magnesium acetate 0.101 mol/L (C

4

H

6

O

4

Mg4H

2

O) (AR) in DMSO.When altering Mg

2+

concentration in the colloid

we kept the content of Mg

2+

plus Zn

2+

to be 0.101 M to guarantee a complete reaction. Solid state nanocrystals were precipitated by adding ethyl acetate into the colloid. The precipitates were then centrifugated at 10 000 r/min for 10 min

washed with ethanol and dried at 80 ℃. The phase structure

morphology and optical properties of the samples were characterized by X-ray diffraction (XRD)

Fourier transform infrared spectrometry (FTIR)

transmission electron microscope (TEM)

absorption spectra (UV-vis)

room temperature photoluminescence (PL) and electron paramagnetic resonance (EPR). The results indicated that Mg

2+

ions partially take interstitial positions in ZnO NCs. When activated by 342 nm laser

the Mg doped ZnO NCs emit strong greenish white light with emission peak at about 500 nm. With higher Mg doping content

the NCs become smaller and the luminescence get stronger. Quantum yield of 20% Mg doped ZnO NCs is 22.8%. The partially interstitial doping Mode introduced Zinc vacancies (V

Zn

) and interstitial Mg

2+

(I

Mg

) into the doped NCs

which were responsible for the enhanced greenish white light emission. Our findings provide a comprehensive understanding of effects of Mg doping on the microstructure and electronic properties of ZnO prepared at low temperature.