While reading the Targum Rishon on Esther Here it seems to me that it is implying that Mordechai had worn tefillin of gold.
טוֹטְפָן דְמַקְבְּעִין בְּדַהֲבָא דְיָדְעִין
Is that halachically permissible, and are there other sources that talk?
A related question about mordechai wearing tefillin?, any further sources regarding him wearing tefillin is greatly appreciated.