A novel Eu-dependent G-La2Si2O7 single matrix phosphor for white light-emitting diodes

Abstract

A novel G-La2Si2O7: Eu phosphor has been synthesized through SiC-reduction assisted with sol-gel method. Divalent Eu2+ and trivalent Eu3+ luminescent centers coexist in G-La2Si2O7: Eu lattice. Furthermore, two types of Eu2+ luminescent centers exist in G-La2Si2O7: Eu lattice, labeled as Eu1 and Eu2, arising from two La3+ crystallographic sites in G-La2Si2O7 host. Eu1 represents blue band emission while Eu2 shows green-yellow emission. Eu2+ selective occupation introduces Eu2+ large-scale blue-yellow regulation. Eu3+ shows typical red sharp line emission mainly located at 593 nm and 611 nm assigned to 5D0→7FJ (J = 1, 2) transitions. The luminescence process in G-La2Si2O7: Eu is discussed in details. Energy transfer processes from Eu3+ to Eu1 and Eu2, Eu1 to Eu2 occurs in G-La2Si2O7: Eu lattice. The influence of Eu dopant concentration is explored. As Eu increases, the dominant emission changes from Eu2+ to Eu3+. The coexistence of Eu1, Eu2 and Eu3+ brings G-La2Si2O7: Eu blue to red regulation. Fixing Eu doping at 0.5%, G-La1.99Si2O7: 0.01Eu sample shows a single-phased white light-emitting phosphor. At ultraviolet light 254 nm excitation, the emission spectrum approximate to full spectrum with a high rendering index of Ra = 91 is obtained using La1.99Si2O7: 0.01Eu sample at 254 nm excitation. Besides, G-La2Si2O7: Eu represents a good fluorescent thermal stability with luminous intensity keeping 80% (160 °C) of that at room temperature (30 °C), indicating G-La2Si2O7: Eu is a great potential single-matrix candidate in nUV-chip WLEDs.