We attempted several solid-state crystal growth methods for Cs 3 Eu(PO 4 ) 2 . The first followed a procedure for Cs 3 Ln(PO 4 ) 2 (Ln: Y, Gd) that uses a Cs 2 CO 3 -H 3 BO 3 flux. After rinsing the flux off with water, we only recovered amorphous product. The second procedure adapted a Rb 3 Ln(PO 4 ) 2 (Ln: Y, Dy-Lu) growth procedure 54 by using a eutectic Cs 2 CO 3 -CsF flux with (NH 4 ) 2 HPO 4 and Eu 2 O 3 in the stoichiometric ratio. After rinsing off the flux with water, only Eu 2 O 3 remained. Additional details are in the Supporting Information.