Revealing Eu3+-doped yttrium pyrogermanate as a soft UV excitable phosphor: retaining the pros of the commercial phosphor and compensating for the cons

Abstract

A paucity of red emitting phosphors efficiently excitable in the soft UV region has been a huge barrier in solid state lighting applications from the combination of a near-UV LED exciting chip and down conversion phosphors. The present work unveils the competence of an Eu-doped yttrium pyrogermanate phosphor (Y₂Ge₂O₇:Eu) efficiently excitable in the soft-UV region. Single phase Y₂Ge₂O₇:Eu with 2–10% Eu content was prepared by conventional solid-state reaction and thoroughly characterized using XRD, FTIR, RAMAN and XPS techniques. To examine the potential of the Y₂Ge₂O₇:Eu phosphor, its photoluminescence behavior was compared with standard commercial red phosphor Y₂O₃:Eu. Remarkably, the results reveal that Y₂Ge₂O₇:Eu retains the pros of the commercial phosphor and compensates for its cons. Whilst the emission profile, decay lifetime and internal quantum efficiency of Y₂Ge₂O₇:Eu are almost identical to those of Y₂O₃:Eu, its Eu-incorporation capacity without concentration quenching is as high as 10% contrary to 5–6% of Y₂O₃:Eu owing to the less dense distribution of Y-sites in the Y₂Ge₂O₇ host. High loading of Eu-content makes Y₂Ge₂O₇:Eu suitable for high contrast displays. Whereas the Y₂O₃:Eu phosphor has negligible absorption efficiency in the soft UV region, the Y₂Ge₂O₇:Eu phosphor has its maximum absorption efficiency around 390 nm nicely aligned with the emission of near UV LED chips. DFT calculations revealed that relatively deeper positioning of the Y₂Ge₂O₇ valence electron energy states and associated covalency are decisive for its demonstration of competing performance. Successful dispersion of Y₂Ge₂O₇:Eu inside a polymer matrix further endorses its potential towards future flexible device applications.