VUV–Vis Luminescent Properties of BaCaBO3F Doped with Ce3+ and Tb3+

The BaCaBO 3 F wide band gap host and the charge-compensated phosphors BaCaBO 3 F:Ln 3+ (Ln = Ce, Tb, Gd) and BaCaBO 3 F:Ce 3+,Tb 3+ 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 BaCaBO 3 F:Ce 3+ . The 5d 1 decay lifetime is 29 ns at x ∼ 0.005. Concentration quenching occurs for Ba 1–2 x Ce x Na x CaBO 3 F with maximum intensity at x ∼ 0.035 and with critical distance R c = 17.7 Å. An unusual broad, intense band in the excitation spectrum of BaCaBO 3 F:Gd 3+ is assigned to a near-defect exciton. Very weak emission from 5 D 3, and intense green emission from 5 D 4, has been assigned for BaCaBO 3 F:Tb 3+ . In the VUV region, the spin-allowed and the spin-forbidden 4f 8 → 4f 7 5d transitions are observed. The codoped system BaCaBO 3 F:Ce 3+,Tb 3+ exhibits emission color tunability when varying the excitation wavelength or the dopant ion concentration. The energy transfer from Ce 3+ to Tb 3+ takes place in the fast migration regime with k ET ∼ 10 6 –10 7 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.