  Emission-line stars in young open clusters are identified to study their
properties, as a function of age, spectral type and their evolutionary state.
207 open star clusters were observed using slitless spectroscopy method and 157
emission stars were identified in 42 clusters. We have found 54 new
emission-line stars in 24 open clusters, out of which 19 clusters are found to
house emission stars for the first time. About 20% clusters harbour emission
stars. The fraction of clusters housing emission stars is maximum in both the
0--10 and 20--30 Myr age bin ($\sim$ 40% each) and in the other age bins, this
fraction ranges between 10% -- 25%, upto 80 Myr. We have used optical colour
magnitude diagram (CMD) along with Near-IR Colour-Colour diagram (NIR CCDm) to
classify the emission stars into Classical Be (CBe) stars and Herbig Be (HBe)
stars. Most of the emission stars in our survey belong to CBe class ($\sim$
92%) while a few are HBe stars ($\sim$ 6%) and HAe stars ($\sim$1%). The CBe
stars are located all along the MS in the optical CMDs of clusters of all ages,
which indicates that the Be phenomenon is unlikely due to core contraction near
the turn-off. Most of the clusters which contain emission stars are found in
Cygnus, Perseus & Monoceros region of the Galaxy, which are locations of active
star formation. The distribution of CBe stars as a function of spectral type
shows peaks at B1-B2 and B6-B7. Our results indicate there could be two
mechanisms responsible for the CBe phenomenon. Some are born CBe stars (fast
rotators), as indicated by their presence in clusters younger than 10 Myr. Some
stars evolve to CBe stars, as indicates by the enhancement in the fraction of
clusters with CBe stars in the 20-30 Myr age bin.
