A high efficiency broad-band near-infrared Ca2LuZr2Al3O12:Cr3+ garnet phosphor for blue LED chips

Abstract

The garnet Ca₂LuZr₂Al₃O₁₂ (CLZA) is a promising broad-band NIR phosphor for blue LED chips when it is doped with Cr³⁺. The photoelectric efficiency of the pc-LED fabricated from CLZA:Cr³⁺ and a 460 nm LED chip, in the 750–820 nm spectral range, was 4.1%, which was superior to the efficiency of a tungsten lamp (2.9%). In CLZA’s structure, Cr³⁺ occupied Ca²⁺/Lu³⁺ and Zr⁴⁺ sites and showed two luminescence centers. The crystal strength parameters of Ce³⁺ and Cr³⁺ were calculated to show the coordination environment of the dodecahedral and octahedral sites in CLZA. Low absorbance of Cr³⁺ was the main constraint on quantum efficiency. Ce³⁺ was thus introduced as a sensitizer to improve the absorbance. An efficient energy transfer process can be observed between Ce³⁺ and Cr³⁺ in CLZA. The temperature dependent properties of CLZA:Cr³⁺ were also studied. Two thermal processes (thermal quenching and thermal ionization) were observed and discussed in detail.