High-Luminance Red Ba₂CaB₂Si₄O₁₄: Eu³⁺ with “Abnormal” Thermal Stability and Adjustable Photoluminescence from Defect Regulation and Energy Transfer via Dy³⁺ Codoping for “Warm” Illumi

In pursuit of illumination-grade wLEDs, innovative red-emitting phosphors with sufficient luminance and thermal stability are required. Herein, a Eu3+-incorporated Ba2CaB2Si4O14 (BCBS) phosphor, exhibiting relatively low efficiency, poor thermal stability, and red line peak photoluminescence (PL) at 614 nm, is preliminarily obtained as a result of Eu3+ 4f–4f transitions. The Rietveld refinements and density functional theory (DFT) calculations indicate that Eu3+ is energetically favored in Ca2+ sites. To overcome the above issues of BCBS: Eu3+, heterovalent Dy3+ is codoped into the phosphor to simultaneously realize: (i) ultrahigh thermal stability of red PL based on structure tailoring and trap regulation associated with both Dy(Eu)Ca• and VO″ defects. For comparison, by tridoping Na+ at the expense of Dy(Eu)Ca• via Dy(Eu)3+ + Na+ → 2Ca2+, the red PL performance is becoming very bad and even worse than that of BCBS: Eu3+, indicating that Dy(Eu)Ca• plays a major role, though the effect of VO″ cannot be completely ruled out, (ii) energy transfer (ET) from Dy to Eu for enhancing PL efficiency/intensity, and (iii) color-tunable PL, including “warm” white light, by combination of both autologous “cool” white PL from Dy and red emission from Eu. The assembled phosphor-converted white light-emitting diode (pc-wLED), adopting single-phase BCBS: Dy3+/Eu3+ with n near UV (nUV) LED chip via a remote “capping” packaging strategy, is a promising candidate to be applied as a white-emitting phosphor in wLEDs. Meanwhile, due to a strong mutual relationship between the intensity ratios of PL bands from magnetic/electric dipole transitions (EDT/MDT) for either Dy (Y/B) or Eu (R/O) and the crystal field environment, the obviously visual PL color change under distinct pressures in a wide range of pressure fluctuations indicates that the phosphor could also be used as a potentially optical pressure sensor with high sensitivity.