The spontaneous emission properties of a single layer organic film in flat optical microcavity were studied. The optical microcavity was formed by a layer of a Tris(8-quino-linoloato) aluminum (Alq) film sandwiched between a quarter-wavelength distributed Bragg reflector (DBR) and a Al metallic reflector. The DBR used here is a chirped one

the structure of which is G[H

1

L

1

]

6

[H

2

L

2

]

6

[H

3

L

3

]

4

H .There the G label represents the glass substrate

the notation [H

1

L

1

]6 implies a quarter-wave of high-index material H

followed by a quarter-wave of low-index material

L

and 6 times. The high-index material is TiO

2

with a refractive indices of 2.0

the low-index material is SiO

2

with a refractive indices of 1.46. The Bragg wavelength of the three stacks is 430nm

570nm and 630nm

rspectively. The stopband range of the DBR was extended from 420nm to 650nm.The PL spectrum of the microcavity and that of Alq film was compared at the same excitation condition. It showed that the PL spectrum of Alq film is a wider band

centered at 521nm with a FWHM of 93nm. The PL of the microcavity exhibits amultimode emission that locates at blue

green and red spectral region. It showed that there are 4 peaks in the PL spectrum of the microcavity. The three strong peaks are located at 497nm

555nm and 615nm

respectively. The other weaker peak is located at 449nm. A strong spectral narrow from 100nm (full width half maximum)of film to 5.6nm of microcavity in PL is observed. The results implied that using microcavity structure is a useful way to achieve multi-color emission.