Sol-gel processing of BaMgF₄-Eu²⁺ thin films and their violet luminescence

BaMgF₄-Eu²⁺ thin films were prepared from trifluoroacetate precursor solutions by a sol-gel method and their violet luminescence was investigated. A (Ba,Eu)MgF₄ phase was obtained by heating the spin-coated precursor films at temperatures of 550-650°C. The reduction of Eu³⁺, which originated from Eu(CH₃COO)₃·4H₂O in the precursor, to Eu²⁺ in the heat-treated films was evidenced by the strong, broadband 4f-5d excitation at 290 nm and emission at 420 nm in photoluminescence measurements. The intensity of violet luminescence of Eu²⁺ depended on the heating temperature, heating time and the Eu concentration. The strongest violet emission was observed with the BaMgF₄-Eu (15 mol%) film that was heated at 650°C for 10 min under the present experimental conditions.