Current-voltage characteristics of silicon carbide luminescence
To emit light your recombination needs to occur all at once across the semiconductor bandgap. In forward bias your electrons move into an excited state in the metal, and then quickly lose their energy to heat in the metal rather than to a photon.
Figure 1.6 shows a fairly standard looking diode I-V curve. Apparently in this case you enter reverse bias by applying a positive voltage to the steel wire. It looks like you have substantial light emitted above about 3 V forward bias and about 30 V reverse bias.