Novel composite color converters based on Tb1.5Gd1.5Al5O12:Ce single crystalline films and Y3Al5O12:Ce crystal substrates

Abstract

In this study, the structural, luminescence and photoconversion properties of novel composite color converters based on Tb_1.5Gd_1.5Al₅O₁₂:Ce (TGAG:Ce) single crystalline films, grown by the liquid phase epitaxy method onto Y₃Al₅O₁₂:Ce (YAG:Ce) single crystal substrates, are investigated. The luminescence and chromaticity properties for the set of TGAG:Ce SCF/YAG:Ce composite color converters, including color coordinates, color rendering index (CRI), and luminous efficacy, were studied by varying the thickness of the TGAG:Ce film in the 12–48 μm range and the Ce³⁺ concentration in the 0.1–0.5% range in YAG:Ce substrates. Such combination of different YAG:Ce substrates with various TGAG:Ce films enables tuning the white light tones from cold white (correlated color temperature (CCT) > 6000 K) to neutral white (6000 K > CCT > 3300 K). The theoretical white light color coordinates on the chromaticity diagram were almost achieved for TGAG:Ce film/YAG:Ce (0.5 mm) crystal converters with a film thickness between 19 and 25 μm under 465 nm LED excitation, with the corresponding CRI values in the 79–74 range. The developed composite color converters allow the problem of a high color temperature and low color rendering index of conventional WLEDs based on conventional YAG:Ce phosphor converters to be solved.