Colossal Chromatic Shift in the Ba₂Ca₂B₄O₁₀:Ce³⁺ Phosphor

Abstract

Developing high-color-quality white light-emitting diodes (LEDs) is crucial for energy-efficient light bulbs and modern flat panel displays. Creating the luminescent phosphors that enable these advanced lighting technologies requires stable photoluminescence under varying temperatures. In this study, we examine Ba2Ca2B4O10 substituted with Ce3+, which emits an efficient blue-cyan light (λem ≈ 455 nm and a quantum yield of 74%) that is required for high color rendering lighting. Synchrotron powder X-ray diffraction and optical spectroscopy reveal that the broad emission band is attributed to Ce3+ ions occupying two crystallographically independent Ba2+ positions in the host crystal structure. However, temperature-dependent luminescence measurements unveil a surprising phenomenon: a significant blue shift (from 460 to 415 nm) accompanied by a drastic narrowing of the total emission bandwidth (from 140 nm, 6900 cm–1 to 58 nm, and 3200 cm–1). This extreme optical response arises from two simultaneous thermal quenching mechanisms─site preferential quenching and high thermal expansion (αV ≈ 5.39 × 10–5 K–1). Consequently, the phosphor experiences a chromatic shift that transforms a fabricated prototype light bulb’s perceived color from functional white light to an undesirable yellow-green hue. These findings underscore the considerable impact of chromatic instabilities in phosphors and the effects they can have on the performance of LED lighting.