Host sensitisation of Tb ³⁺ emission in K ₇ CaY ₂ (B ₅ O ₁₀ ) ₃

We discovered a very intense defect related to emission in the title compound for the first time. This emission is in ultraviolet A (UVA) region. For more widespread applications, luminescence in the visible region is more relevant. Host sensitisation of well-known activators can result in the emission we are looking for. In this host, Y-Y distances are large (6.63 Å), and one may expect large concentrations of trivalent lanthanides to be incorporated without concentration quenching. Results on host sensitisation of Tb3+ emission in K7CaY2(B5O10)3 borate are described here. No host sensitisation using 290 nm excitation has been observed in other borates. The phosphor shows intense green emission typical of Tb3+ (colour coordinates x = 0.26, y = 0.57). In the excitation spectra, two strong bands, one related to f-d transitions of Tb3+ (238 nm) and the other corresponding to the host sensitisation (290 nm) are seen. Host to Tb3+ energy transfer is studied through PL emission spectra and lifetime measurements. The lifetime of host emission decreased from 1.254 μs to 200 ns after Tb3+ doping. As Tb3+ concentrations rise to 20 mol. %, the transfer efficiency rises to 84%.