Insight into Tendentious\nMultisite Colonization, Site\nEnvironment Modulation, and Energy Transfer of Steady Ba<sub>2</sub>CaB<sub>2</sub>Si<sub>4</sub>O<sub>14</sub>: Ce/Tb/Sm/Sr/Na toward\nnUV-Pumped

With the growing public awareness of protecting vision\nand prevention\nof hazardous effects, there is much-needed research on a “healthy”\nfull visible spectrum under near-ultraviolet (nUV) excitation in phosphor-converted\nwhite light-emitting diodes (pc-wLEDs) to fill the “cyan gap”\nand avoid employing a blue LED chip. Herein, a novel series of borosilicates\nBa<sub>2</sub>CaB<sub>2</sub>Si<sub>4</sub>O<sub>14</sub> (BCBS):\nCe<sup>3+</sup>/Tb<sup>3+</sup>/Sm<sup>3+</sup>/Sr<sup>2+</sup>/Na<sup>+</sup> phosphors, presenting color-tunable photoluminescence (PL),\nhigh quantum yield (QY), and thermal stability, were designed and\nsynthesized via a facile solid-phase reaction. The Rietveld analyses,\ndensity functional theory (DFT) simulations, and theoretical calculations\nof bond energy together imply the site occupations of Ce/Tb/Sm on\nBa<sup>2+</sup>/Ca<sup>2+</sup> sites with a preferred location on\nCa<sup>2+</sup> over the Ba<sup>2+</sup> site. The broad/bright cyan-PL\nfrom BCBS: Ce under nUV excitation is associated with the allowed\nf–d transitions of Ce<sup>3+</sup> and dual-site occupancies.\nThe forbidden f–f transitions of both the green-PL of Tb and\nthe red-PL of Sm were insensitive to the site environment and helpful\nto PL color regulation. The cascading Ce → Tb → Sm energy\ntransfer is confirmed, where Tb is regarded as an energy transfer\n(ET) bridge to avoid the metal–metal charge transfer (MMCT)\neffect. The introduction of Na<sup>+</sup> as both flux and charge\ncompensator is for the sake of decreasing defects from heterovalent\nsubstitutions and regulating morphology. Further incorporation of\nSr<sup>2+</sup> is to modulate the lattice environments of dopants\nfor controlling the shift of PL. Finally, as a proof-of-concept implement,\na pc-wLED assembled by BCBS: Ce/Tb/Sm/Sr/Na and an nUV LED chip via\na remote “capping” packaging strategy show attractive\nperformance.