Nonlinear plasmonics is a growing field since the power threshold for observable nonlinear light emission of new frequencies can be lowered greatly due to dramatic electromagnetic field confinement. Along another research line, 2D electron gases (2DEGs) formed at interfaces of oxides have been drawing broader attention globally because the metallic constituents can be eliminated, and hence the inherent huge loss associated with uses of metals in plasmonic applications can be circumvented. Once the nonlinear materials are proximal to 2DEGs and surface plasmon polaritons (SPPs) are excited, the electromagnetic field can be strengthened several orders in magnitude. Consequently, the nonlinear processes can take place at a quite low incident light power. Considering much greater dispersion of SPPs, the second order nonlinear processes can be easily realized in terms of meeting phase matching conditions. In this paper, nonuniform 2DEG formed at the interface of a Z-cut Fe doped LiNbO3 (LN) slab and an indium-tin-oxide (ITO) thin film was analyzed with semi-classical Thomas Fermi screening model, and dispersion of index of refraction was given accordingly. A laser beam at 532 nm and a white light source illuminated the slab from the opposite directions collinearly and a remarkable light emission redistribution was observed with a continuous spectrum of short visible light peaked around 437 nm. Several confirming experimental results with ITO coated Y-cut slabs are presented and phase grating mediated SPP excitation is proposed to explain the related findings, suggesting that second order nonlinear processes strengthened by SPPs are behind the light emission redistribution.