We have used low energy electron-excited nanoscale (LEEN) luminescence spectroscopy, a low energy variant of cathodoluminescence spectroscopy, to measure localized states at 4H- and 6H SiC surfaces and interfaces. Both discrete and continuum states appear across the band gap that depend sensitively on surface chemical treatment, thermal processing, or metallization. These localized states form not only as a result of interface chemical bonding but also due to the formation of new local structures/polytypes. Luminescence measurements reveal a striking polytype change of 4H- to 3C-SiC in quantum-scale transformation bands activated by high temperature thermal annealing and high n-type doping. Deep level correlations with Schottky barriers highlight the importance of interface chemical as well as structural interactions.