Owing to its properties of high-luminescent efficiency

chemical stability and wetresistence

Zn

2

SiO

4

exhibitsmore excellent performance than the sulfides as luminescent hostmaterial. Zn

2

SiO

4

:Mn

2+

(willemite) is an efficient phosphor for plasma display

cathodoluminescent and electroluminecent displays.Over the past few decades

researchers have studied intensely about factors influencing on the photolumines-centproperties of Zn

2

SiO

4

:Mn

2+

such as calcining temperatures

concentration of Mn

2+

atmosphere of heat treatment

various preparationmethods.However

the pH value of the Zn

2

SiO

4

:Mn

2+

precursor sol also plays an important role in its luminescent properties.Herein

we investigate the effects of pH value of the precursor sol

heating atmosphere (oxidizing

neutralprotecting and reducing) and calcining temperature on the photo-luminescent intensity of Zn

2

SiO

4

:Mn

2+

phosphor powder.Zn

2

SiO

4

:Mn

2+

phosphors have been prepared via a solgel route.DifferentpH values of the sol resulted in differentgeling time and the sol with pH value lower than 3 could notbe gelatinized.After preheating at 600℃

Zn

2

SiO

4

:Mn

2+

precursorswere calcined in different atmosphere (air

N

2

and mixture of 10% H

2

+90% N

2

) atheating temperature varing from 800℃ to 1100℃.The structure of Zn

2

SiO

4

:Mn

2+

has been characterized by X-ray diffraction (XRD)

which shows thatall the phase of phosphors is with -Zn

2

SiO

4

phase.The phosphor prepared from the sol with pH of 4.34 has the best crystallinity.Scanning electronmicroscope (SEM) is used tomeasure the particle size of the Zn

2

SiO

4

:Mn

2+

phosphors and the mean size of the phosphor obtained from the solwith pH value of 4.34 is about 100 nm

larger than the size of the phosphors obtained from sols with pH values of 5.32 and 6.53.The results of photoluminescent (PL) spectra indicate that the PL intensity of the phosphor increaseswith increasing the pH value ofprecursor sol

and themaximum was obtainedwhen the pH value of precursor sol is 4.34.Because the phosphor obtained from the sol with pH value of 4.34 has bestcrystallinity

and its particle size is larger

leading to smaller specific surface area.When the specific surface area is smaller

there are lower defects in the surface ofparticles and fewernonradiative transitions appear.Additionally

the hydrolysis and polyconden-sation reactions of the precursor solwith pH value of 4.34 have been carried throughly and properly

resulting in the well dispersion of the Mn ions.The emission intensity of Zn

2

SiO

4

:Mn

2+

phosphors calcined in themixture of nitrogen and hydrogen is stronger than those of the phosphors calcined in the other heating at mosphere.Reducing atmosphere could easily split Mn-Mn pair and produce large number of is olated Mn ions.With H

2

existing in the heating at mosphere

more Zn ions in cline to be volatilized and more Mn ionswould substitute for Zn ions.There fore

the PL intensity of Zn

2

SiO

4

:Mn

2+

phosphors is the strongestwhen the pH value of the precursor sol is 4.34 and the phosphors are calcined in the mixture of N

2

and H

2

at 900℃.