Luminescence from an electrode during photoelectrochemical reaction is observed but has not been used as an evaluation tools probably due to its difficulty of the evaluation. When the method of in-situ photoluminescence (PL) measurement is established, it is expected that the results can asisst the analysis of relaxsation process of the excited carrier in a photoelectrode with using the difference of the PL signal with and without photoelectrochemical reaction. In this report, the possibility of the in-situ PL with photoelectrochemical reaction is discussed.

The samples used in the experiments of n-type GaN are suitable for the evaluation because of the ability of water splitting without bias and its chemical stability. The n-type GaN working photo-irradiated electrode was directly connected with a counterelectrode of Pt wire. The light sources were 325.0 nm He-Cd laser and Xe-lamp with high cut filter. A 1.0 mol/L NaOH aqueous solution was used as an electrolyte. The PL measurement was perfomed in the electrolyte through a qualtz cell with and without photoelectrochemical circuit.

Since the experiments was required to perform at room temperature, the major signals from the n-type GaN were so-called XL of near band emission and YL of around 2.2 eV. The YL is defined to be a luminescence from band to deep acceptor transition.

The first trial was performed with the light source of 325.0 nm He-Cd laser. Although the light spot was expanded for the photoelectrochemical process use, the light intensity distribution and the light spot area was not enough for the detailed evaluation of the PL signal difference with and without photoelectrochemical process. Even though, the difference of PL signal was obtained and the intensity decreasing ratio of XL was larger than that of YL after turn-on the photoelectrochemical circut.

In order to stabilize the irradiated light intensity, Xe-lamp with 370 nm high cut filter was used as a light source. Since the excited light was overlapped the XL at around 370 nm, the XL was not evaluated for this case. The difference of YL signal with and without photocurrent circuit was clealy observed, the intensity decreasing ratio of YL with filtered Xe-lamp was larger than that of 325.0 nm He-Cd laser excited. From the comparison with the relaxsation model of the relationship among XL, YL, and photocurrent for water splitting, the result looks consistent.