A novel high color purity blue-emitting Tm3+-doped β-Ca3(PO4)2-type phosphor for WLED application

Abstract

The series of Tm-doped phosphates Ca9-xZnxLa0.9(PO4)7:0.1Tm3+ for phosphor-convertible white LEDs (pc-WLED) with β-Ca3(PO4)2-type structure were synthesized using a standard high temperature route. Intense blue emission in the visible spectrum was observed due to 4f-4f transitions in the Tm3+ ion. The phosphates have been characterized by powder X-ray diffraction (PXRD), second harmonic generation (SHG), and luminescence spectroscopy. These phosphors show a satisfactory blue performance due to the 1D2 – 3F4 (≈ 450 nm) transition of Tm3+ excited by near-UV light (358 nm). The crystal structure transforms R3c → R3¯c upon Ca2+ → Zn2+ substitution, and it leads to growing of the integral intensity in 4 times compared with unsubstituted phosphate. Rising of color purity peaking at x = 1 was also observed. The obtained characteristics are superior to than that for the commercial blue phosphor BaMgAl10O17:Eu2+. Generally, Ca9-xZnxLa(PO4)7:Tm3+ phosphates are a new kind of potential blue emitting phosphors for white light-emitting diodes.