The Er

3+

/Yb

3+

codoped TeO

2

-WO

3

-ZnO (TWZ) glass samples with same doping concentration and different thickness were prepared. The absorption spectra

1.5 μm emission spectra and fluorescence lifetimes of Er

3+

excited by 970 nm

were measured. The absorption cross-section was calculated based on measured absorption spectra at room temperature. The emission cross-sections were calculated by McCumber theory. The effect of radiation trapping on the spectroscopic properties of Er

3+

in TWZ glass was discussed. Because of the high refractive index of the glass and very large overlapping around 1.5 μm between the absorption cross section and the emission cross section of Er

3+

in TWZ glass

the radiation trapping in the TWZ glass samples was very strong. The radiation trapping became stronger with the increase of the thickness of samples. Due to the effect of the radiation trapping

the measured fluorescence lifetime was longer than the calculated one

which caused the quantum efficiency large than 100%. The emission spectra were also broadened and the emission peak wavelength shifted to the longer wavelength slightly. When the sample thickness increased from 0.50 mm to 3.15 mm

the fluorescence lifetime increased from 2.60 ms to 3.10 ms and the quantum efficiency increased from 111% to 132%. At the same time

the fluorescence effective line width

Δλ

eff

increased from 76.2 nm to 91.7 nm and the emission intensity ratio of the main peak to the second peak

I

s

/I

p

also increased gradually. The fitting results showed that the Δλ

eff

increased linearly with the increasing of the ratio value of I

s

/I

p

. Based on the obtained linear equation for Δλ

eff

and I

s

/I

p

the effective line width in the glass sample without the exis-tence of radiation trapping was deduced

which was 72.1 nm. The value was very close to the Δλ

eff

calculated from the emission cross-section curve

which was 70.3 nm. So we suggested that the Δλ

eff

calculated from the emission cross-section curve could be used to determine the Δλ

eff

of Er

3+

emission at 1.5 μm without the radiation trapping effect. For the first time

the opinion that the ratio of the I

s

/I

p

to the σ

es

/σ

ep

or the difference between the I

s

/I

p

and the σ

es

/σ

ep

can be used to evaluate the radiation trapping of Er

3+

at 1.5 μm band. Here the σ

es

and the σ

ep

are the emission cross sections at wavelength of the second peak and the strongest peak

respectively

calculated by McCumber theory.