First, for phosphorescence excitation wavelength, it doesn't have to be MLCT band. It may be LLCT, ILCT, IL ... It depends on what transitions the material has.

You should measure the UV/VIS absorption spectrum first. Then, identify the lowest-energy absorption band and use it for excitation to obtain the emission spectrum. Then, take an excitation spectrum of the emission. The excitation spectrum should look very similar to the absorption spectrum. Moreover, you should also try other excitation wavelengths instead of doing measurement with just one excitation wavelength. In most cases, you will obtain the same emission spectrum.

If you are measuring a solution sample, make sure that the absorbance is not higher than 0.5. Otherwise, the excitation spectrum may look different from the absorption spectrum due to strong absorption of excitation light in the front part of the cuvette. This applies to instruments whose excitation source, sample, and emission detector form a 90 degree angle. Hope this helps.

Thanks for your reply