Spectral indices used for the spectral type estimation of the NIR spectral type. Our targets are represented by red stars and are numbered from 1 to 6: 1 = 2M2213, 2 = EROS J0032, 3 = 2M2208, 4 = 2M2126, 5 = 2M2322, 6 = DENIS 1245 and 7 = Cha1305. The black lines represent the three-degree polynomial fit to the field brown dwarfs. We report the index values for objects classified in the optical that are members of young clusters, star forming regions, or nearby associations (YMG), and for dwarfs with low (γ) and intermediate (β) gravity classes (Kirkpatrick 2005).