A new melilite-type rare-earth borate CdTbGaB2O7 and multicolor tunable emission in the CdTb1−xSmxGaB2O7 (0 ≤ x ≤ 0.2) phosphors

Abstract

A new mixed metal borate, CdTbGaB₂O₇, was successfully synthesized using the high-temperature solution method and its crystal structure was determined by single-crystal X-ray diffraction with the following unit-cell data: P2₁m, a = b = 7.3487(1) Å, c = 4.7247(1) Å, V = 255.150(9) ų, and Z = 2. It belongs to a new member of the melilite family, which features a 3D framework consisting of alternately stacked [Ga(B₂O₇)]_n⁵ⁿ⁻ tetrahedral layers and (Cd²⁺/Tb³⁺) cationic layers that are interconnected via B(Ga)–O–(Cd/Tb) bridges. In addition, the solid solutions of CdTb_1−xSm_xGaB₂O₇ (0 ≤ x ≤ 0.2) were prepared via the solid-state reaction method. The combined techniques of XRD, SEM, IR/Raman, XPS and PLE/PL were employed to characterize the products. It was found that the CdTb_1−xSm_xGaB₂O₇ phosphors simultaneously showed green emission of Tb³⁺ at 545 nm and orange emission of Sm³⁺ at 603 nm under excitation at 370 nm. The emission color can be adjusted from green to orange-red by varying the Sm³⁺ doped content via an energy transfer mechanism. For CdTb_0.995Sm_0.005GaB₂O₇, a QY of 13.22% was obtained, and its emission intensity at 423 K was 94% of that at 303 K. These results show that the prepared materials can act as potential color-tunable phosphors for UV w-LEDs.