Energy transfer and colour tunability in UV light induced Tm/Tb/Eu: ZnB glasses generating white light emission.

A promising energy transfer (Tm→Tb→Eu) approach is brought forward to generate white light emission under ultraviolet (UV) light excitation for solid state lightening. Tm/Tb/Eu ions are combinedly doped in zinc borate glass system in view of understanding energy transfer process resulting in white light emission. Zinc borate (host) glass displayed optical and luminescence properties due to formation of Zn(II)-[O(-II)] centres in the ZnB glass matrix. At 360nm (UV) excitation, triply doped Tm/Tb/Eu: ZnB glasses simultaneously shown their characteristic emission bands in blue (454nm: D→F), green (547nm: D→F) and red (616nm: D→F) regions. In triple ions doped glasses, energy transfer dynamics is discussed in terms of Forster-Dexter theory, excitation & emission profiles, lifetime curves and from partial energy level diagram of three ions. The role of Tb in ET from Tm→Eu was discussed using branch model. From emission decay analysis, energy transfer probability (P) and efficiency (η) were evaluated. Colour tunability from blue to white on varying (Tb, Eu) content is demonstrated from Commission Internationale de L'Eclairage (CIE) chromaticity coordinates. Based on chromaticity coordinates, other colour related parameters like correlated colour temperature (CCT) and colour purity are also computed for the studied glass samples. An appropriate blending of such combination of rare earth ions could show better suitability as potential candidates in achieving multi-colour and warm/cold white light emission for white LEDs application in the field of solid state lightening.