This mark doesn’t appear in my reference for Irish makers’ marks. But I offer the following as a possibility:
Jackson’s Silver & Gold Marks of England, Scotland & Ireland illustrates a similarly shaped mark with HL for Henry Lazarus, this mark being noted as between 1813 and 1850. An 1841 Dublin Trades Directory lists Lazarus & Son, Silversmiths at 9 Parliament Street, Dublin. It may be therefore that PL was a member of the Lazarus family.