A color tunable and white light emitting Ca2Si5N8:Ce3+,Eu2+ phosphor via efficient energy transfer for near-UV white LEDs

Abstract

Achieving tunable color and white light emission in a single phase phosphor is a challenging issue. Here, a series of Ce³⁺–Eu²⁺ co-doped Ca₂Si₅N₈ phosphors were successfully synthesized by a high temperature solid state method. Luminescence properties, energy transfer (ET) and thermal quenching of the as-synthesized samples were investigated in detail. The emission color of as-prepared Ca_1.94Na_0.03Si₅N₈:0.03Ce³⁺,yEu²⁺ (0.0000 ≤ y ≤ 0.0035) could be tuned from blue to white light and eventually to orange via ET by changing the Ce³⁺/Eu²⁺ ratio. ET efficiency from Ce³⁺ to Eu²⁺ could reach up to 68.0% and the ET mechanism was demonstrated to be a non-radiative dipole–dipole interaction. More importantly, when y = 0.0012, approximate standard white light was generated with CIE coordinates of (0.335, 0.341). A photoluminescence (PL) mechanism was proposed to understand PL properties and thermal properties of the as-prepared phosphors. Additionally, the achieved white light phosphor Ca_1.9388Na_0.03Si₅N₈:0.03Ce³⁺,0.0012Eu²⁺ had good thermal stability, exhibiting about 75% at 150 °C and 64% at 200 °C of the emission intensity at 25 °C, respectively. The chromaticity shifts of Ca_1.9388Na_0.03Si₅N₈:0.03Ce³⁺,0.0012Eu²⁺ were 0.0032 at 150 °C and 0.0152 at 200 °C, respectively, which were only 27% and 42% of the commercial white-emitting phosphor mixture at the corresponding temperature. Furthermore, a proof-of-concept white LED was fabricated by combining the single component phosphor Ca_1.9388Na_0.03Si₅N₈:0.03Ce³⁺,0.0012Eu²⁺ with a near UV LED chip. All results demonstrate the promising application of the Ca₂Si₅N₈:Ce³⁺,Eu²⁺ single phosphor for near-UV white LEDs.