氮掺杂氧化锌粉末的缺陷研究

Investigation of defects in N-doped ZnO powders prepared by a facile solvothermal method and their UV photocatalytic properties

Pengfei Gu a,Xudong Wang a,*,Tao Li b,Huimin Meng a

a Institute of Advanced Materials and Technology,University of Science and Technology Beijing,30Xueyuan Road,Beijing100083,People’s Republic of China

b Science and Technology on Reliability and Environmental Engineering Laboratory,Beijing Institute of Spacecraft Environment Engineering,104Youyi Road,

Beijing100094,People’s Republic of China

1.Introduction

ZnO is one of the most promising materials for fabricating

optoelectronic devices,owing to its large exciton binding energy of

60meV and wide band gap energy of3.37eV at room temperature.

Intrinsic ZnO is an n-type wide bandgap semiconductor with an

ultraviolet(UV)absorption property.However,ZnO is still

difficulty in obtaining stable p-type conductivity.As we know,

the acceptor dopants in ZnO include lithium[1],copper[2],zinc

vacancies[3],and oxygen interstitials[3],but all of these are deep

acceptors and do not contribute significantly to hole conduction

[4].Until nitrogen(N)is considered to be the most promising p-

type dopant for ZnO due to its similar ionic radius to oxygen,large

solubility,and low ionization energy[5].In addition,N-doped ZnO

shows higher visible-light photocatalytic activity[6,7],therefore

N-doped ZnO was focused.

And in N-doped ZnO,it is found that nitrogen can form two

distinct centers in ZnO material,the molecular nitrogen substitut-

ing for oxygen(N2)O and the isolated nitrogen substituting for

oxygen(N)O[8,9].The neutral molecular nitrogen charge state

(N2)O is a deeper acceptor level[9]than the isolated neutral

nitrogen charge state(N)O[8].In other words,the(N)O acceptors

begin tofill before the(N2)O acceptors.Another argument indicates

that(N2)O is a shallow double donor electrically[10,11]by

theoretical calculations,which leads to the compensation rather

than p-type doping as(N)O.It is important for gaining(N)O

acceptors in N-doped ZnO.

So far,N-doped ZnO has been obtained by direct synthesis or

post-synthesis treatments.Direct synthesis means that N-related

dopants are incorporated into ZnO lattice during growth process,

such as chemical vapor deposition(CVD)methods[11],magnetron

sputtering technique[12],and molecular beam epitaxy(MBE)[13]

in N2O,NH3or N2atmospheres,mechanochemical methods[14],

sol–gel method[15],and hydrothermal[16]or solvothermal

synthesis[17].Whereas,post-synthesis treatments mean that as-

gained ZnO are treated by N source,such as,with NH3[18]at high

temperature heat treatment,or N ions implantation[19].Among

the many methods,either direct synthesis or post-synthesis

treatments,with N2atmospheres is easy to form(N2)O dopants,

due to the high energy of the N B B N bond($9eV)makes it difficult

for its dissociation to achieve isolated nitrogen incorporation[20].

In addition,direct growth or post-synthesis treatments with NH3

or N2O in high temperature also can gain(N2)O dopants[21].One

can expect that using NH3as N source and a low growth

temperature would be favorable for(N)O acceptors into ZnO.Thus

solution-based processes(such as hydrothermal or solvothermal)

favor the fabrication of large scale ZnO crystals at relatively low

temperature with low cost.However,N-doped ZnO by hydrother-

mal or solvothermal synthesis have rarely been reported so far.

Wang et al.[22]reported that hydrothermal growth of N-doped

Materials Research Bulletin48(2013)4699–4703

A R T I C L E I N F O

Article history:

Received19March2013

Received in revised form28June2013

Accepted18August2013

Available online26August2013

Keywords:

A.Inorganic compounds

B.Crystal growth

D.Defects

D.Electronic paramagnetic resonance(EPR)

D.Catalytic properties

A B S T R A C T

A facile synthetic procedure for N-doped ZnO powders was proposed.In this work,N-doped ZnO crystals

were synthesized in diethylene glycol(DEG)with ammonia solution via solvothermal process.

Incorporated N concentration increases with the amount of ammonia solution.In order to confirm the

defects of as-gained ZnO powders,the samples were characterized by XRD,PL,and EPR.In our results,the

N-related defects were considered to be(N)O centers as acceptors,other than(N2)O.And,the donors

defects were confirmed to H i.UV photocatalytic activity of the N-doped ZnO crystals was assessed from

the photodegradation kinetics of methyl orange(MO).The result shows that the UV photocatalytic

activity of N-doped ZnO decreases with the incorporated N concentration.This was caused by abundant

acceptors hindered the photoinduced holes generating.

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*Corresponding author.Tel.:+861062332548;fax:+861080115555741836.

E-mail address:xdwang@(X.Wang).

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