Eu ions were doped into InGaN by organometallic vapor phase epitaxy. The influence of In composition on the optical properties of Eu-doped InGaN (InGaN: Eu) was investigated using photoluminescence (PL), and combined excitation-emission spectroscopy (CEES). The PL spectra of InGaN: Eu showed a new series of emission lines, which became dominant with increasing In content. CEES measurements confirmed that these emission lines originated from a new Eu luminescent center, with In as a second nearest neighbor. Thus, it is possible to distinguish the typical Eu-N related luminescent sites from the new Eu-N-In related luminescent site. Based upon our findings, we propose that Eu3+ ions doped in InGaN could be used as a microscopic probe for the detection of In segregation.