Insight into Tendentious Multisite Colonization, Site Environment Modulation, and Energy Transfer of Steady Ba2CaB2Si4O14: Ce/Tb/Sm/Sr/Na toward nUV-Pumped wLED Application

With the growing public awareness of protecting vision and prevention of hazardous effects, there is much-needed research on a “healthy” full visible spectrum under near-ultraviolet (nUV) excitation in phosphor-converted white light-emitting diodes (pc-wLEDs) to fill the “cyan gap” and avoid employing a blue LED chip. Herein, a novel series of borosilicates Ba₂CaB₂Si₄O₁₄ (BCBS): Ce³⁺/Tb³⁺/Sm³⁺/Sr²⁺/Na⁺ phosphors, presenting color-tunable photoluminescence (PL), high quantum yield (QY), and thermal stability, were designed and synthesized via a facile solid-phase reaction. The Rietveld analyses, density functional theory (DFT) simulations, and theoretical calculations of bond energy together imply the site occupations of Ce/Tb/Sm on Ba²⁺/Ca²⁺ sites with a preferred location on Ca²⁺ over the Ba²⁺ site. The broad/bright cyan-PL from BCBS: Ce under nUV excitation is associated with the allowed f–d transitions of Ce³⁺ and dual-site occupancies. The forbidden f–f transitions of both the green-PL of Tb and the red-PL of Sm were insensitive to the site environment and helpful to PL color regulation. The cascading Ce → Tb → Sm energy transfer is confirmed, where Tb is regarded as an energy transfer (ET) bridge to avoid the metal–metal charge transfer (MMCT) effect. The introduction of Na⁺ as both flux and charge compensator is for the sake of decreasing defects from heterovalent substitutions and regulating morphology. Further incorporation of Sr²⁺ is to modulate the lattice environments of dopants for controlling the shift of PL. Finally, as a proof-of-concept implement, a pc-wLED assembled by BCBS: Ce/Tb/Sm/Sr/Na and an nUV LED chip via a remote “capping” packaging strategy show attractive performance.