VUV–Vis luminescent properties of BaCaBO₃F doped with Ce³⁺ and Tb³⁺

The BaCaBO₃F wide band gap host and the charge-compensated phosphors BaCaBO₃F:Ln³⁺ (Ln = Ce, Tb, Gd) and BaCaBO₃F: Ce³⁺, Tb³⁺ have been synthesized by a solid-state reaction method at high temperature. Their spectroscopic properties in the vacuum ultraviolet (VUV)–vis range have been investigated. The band gap of the host lattice is estimated at 7.8 eV, which is considerably higher than the value found from its diffuse reflectance spectrum. The 5d crystal field level locations, Stokes shift, and Huang–Rhys factor have been determined from the VUV excitation and near-UV emission spectra of BaCaBO₃F: Ce³⁺. The 5d¹ decay lifetime is 29 ns at x ∼ 0.005. Concentration quenching occurs for Ba₁₋₂xCeᵪNaᵪCaBO₃F with maximum intensity at x ∼ 0.035 and with critical distance Rc = 17.7 Å. An unusual broad, intense band in the excitation spectrum of BaCaBO₃F:Gd³⁺ is assigned to a near-defect exciton. Very weak emission from ⁵D₃, and intense green emission from ⁵D₄, has been assigned for BaCaBO₃F: Tb³⁺. In the VUV region, the spin-allowed and the spin-forbidden 4f⁸ → 4f⁷5d transitions are observed. The codoped system BaCaBO₃F: Ce³⁺, Tb³⁺ exhibits emission color tunability when varying the excitation wavelength or the dopant ion concentration. The energy transfer from Ce³⁺ to Tb³⁺ takes place in the fast migration regime with kET ∼ 106–107 s–1 and with energy-transfer efficiency up to 23% for the samples investigated. The mechanism is revealed from energy level and decay measurements. This codoped system exhibits absorption bands near the major Xe discharge wavelengths. Copyright © 2013 American Chemical Society.