Color Tunable Single-phase Cyclosilicate KBaScSi3O9: Eu2+/Tb3+/Sm3+ for n-UV pumped wLEDs

Abstract

The exploration of stable/efficient phosphor for n-UV chip pumped white light-emitting diodes (wLEDs) remains an arduous task. Herein, a novel series of color tunable Eu2+/Tb3+/Sm3+ tridoped Sc-based cyclosilicate phosphors (KBaScSi3O9: Eu2+/Tb3+/Sm3+) have successfully designed and obtained via facile solid-state reaction based on comprehensive consideration of rigidly structural network of host, weak electron-phonon coupling strength and spectral adjustability of codopants via energy transfer (ET). The crystallographic occupancies of Eu, Tb and Sm primary in Ba/K, Ba and Ba sites in the monoclinic host, respectively were determined on the basis of the Rietveld refinements and crystal chemistry rules. The photoluminescence (PL) properties were systematically investigated in conjunction with structural analyses, implying that the ‘warm’ white light with excellent thermal stability is stemmed from combination of optimized blue (Eu2+), green (Tb3+) and red (Sm3+) emissions via Eu → Tb → Sm ET strategy. Interestingly, Tb ions play both roles of green light luminescent center and ET bridge to achieve cascade ET for connecting Eu/Sm ion pairs because of the adverse metal-metal charge transfer (MMCT) effect (Eu2+ + Sm3+ → Eu3+ + Sm2+). Furthermore, the phosphor-converted wLEDs (pc-wLEDs), by encapsulating the optimal KBS: 4%Eu/4%Tb/6%Sm with commercial n-UV LED chip, show high thermal stability with satisfactory electroluminescence (EL) performances. These results indicate the KBS: Eu/Tb/Sm phosphors are potential candidates for application in high power n-UV pumped pc-wLEDs.