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

• Published in: New journal of chemistry 2022-09, Vol.46 (37), p.17755-17766
• Main Authors: Tyagi, Adish, Nigam, Sandeep, Vats, B. G, Sudarsan, V, Majumder, C, Kaiwart, R, Poswal, H. K, Jagannath, Tyagi, A. K
• Format: Article
• Language: English
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d2nj03374g

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 (Y 2 Ge 2 O 7 :Eu) efficiently excitable in the soft-UV region. Single phase Y 2 Ge 2 O 7 :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 Y 2 Ge 2 O 7 :Eu phosphor, its photoluminescence behavior was compared with standard commercial red phosphor Y 2 O 3 :Eu. Remarkably, the results reveal that Y 2 Ge 2 O 7 :Eu retains the pros of the commercial phosphor and compensates for its cons. Whilst the emission profile, decay lifetime and internal quantum efficiency of Y 2 Ge 2 O 7 :Eu are almost identical to those of Y 2 O 3 :Eu, its Eu-incorporation capacity without concentration quenching is as high as 10% contrary to 5-6% of Y 2 O 3 :Eu owing to the less dense distribution of Y-sites in the Y 2 Ge 2 O 7 host. High loading of Eu-content makes Y 2 Ge 2 O 7 :Eu suitable for high contrast displays. Whereas the Y 2 O 3 :Eu phosphor has negligible absorption efficiency in the soft UV region, the Y 2 Ge 2 O 7 :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 Y 2 Ge 2 O 7 valence electron energy states and associated covalency are decisive for its demonstration of competing performance. Successful dispersion of Y 2 Ge 2 O 7 :Eu inside a polymer matrix further endorses its potential towards future flexible device applications. This article presents the synthesis of a single-phase red emitting Y 2 Ge 2 O 7 :Eu 3+ soft-UV excitable phosphor with up to 10% Eu 3+ content. Experimental and theoretical exploration has established its relative potential with respect to the commercial Y 2 O 3 :Eu 3+ phosphor.