Highly efficient phosphor materials with superior thermal stability are indispensable for phosphor-converted white light-emitting diodes (pc-WLEDs) solid state lighting. In order to obtain a high quality warm white light, near-ultraviolet (n-UV) chips combined with trichromatic phosphors have be extensively studied. Among them, the development of efficient blue phosphor remains a challenging task. In view of the close correlation between 5d−4f transitions of rare earth ions and the coordination environment of host lattice, many studies have been dedicated to improving the photoluminescence performances by modifying the lattice coordination environment including the lattice rigidity and symmetry. In this work, we reported highly efficient blue-emitting Eu 2+ -doped BaAl 12 O 19 (BAO) phosphors with excellent thermal stability, which were prepared via the traditional high-temperature solid state reaction routes. According to the X-ray powder diffraction (XRD) Rietveld refinement analysis, BAO owned a highly symmetric layer structure with two Ba polyhedrons, marked as Ba(1)O 9 and Ba(2)O 10 , respectively. The diffuse reflectance spectra revealed the optical band gap to be 4.07 eV. Due to the suitable optical bandgap, the Eu 2+ ions could realize a highly efficient doping in the BAO matrix. The photoluminescence excitation (PLE) spectra for asprepared BAO:Eu 2+ phosphors exhibited a broad absorption band in the region from 250 to 430 nm, matching well with the n-UV LED chip. Under the UV radiation, it is highly luminous (internal quantum yields (IQYs) = 90%) with the peak around 443 nm. Furthermore, the color purity of BAO:Eu 2+ phosphors could achieve 92%, ascribing to the narrow full width at halfmaximum (fwhm = 52 nm), which was even much better than that of commercially available BAM:Eu 2+ phosphor (color purity = 91.34%, fwhm = 51.7 nm). More importantly, the as-prepared BAO:Eu 2+ phosphor showed extra high thermal stability when working in the region of 298−550 K, which was a bit better than that of commercial BAM:Eu 2+ phosphors. According to the distortion calculation of Ba crystallographic occupation, the superior thermal stability could be attributed to the highly symmetric crystal structure of BAO host. In view of the excellent luminescence performances of BAO:Eu 2+ , it is a promising blue-emitting phosphor for n-UV WLED. ■ INTRODUCTIONRecently, phosphor-converted white light-emitting diodes (pc-WLEDs) lighting has been widely integrated into our daily lives

Cation-substitution-induced controllable luminescence tuning could efficiently optimize and improve the luminescence performances of novel phosphor materials for realizing high-quality lighting. As important members of the orthophosphate family, ABPO4 (A = alkali metal Li, Na, K, Rb, Cs; B = alkali earth metal Mg, Ca, Sr, Ba) offers an abundant cation lattice environment for rare earth ions. Herein, we successfully prepared a broad-band red-emitting CsMgPO4:Eu2+ phosphor with an emission peak at 628 nm (fwhm = 118 nm). A series of cation-substitution strategies are designed to adjust and enhance its luminescence performances. The corresponding mechanisms are also investigated and proposed reasonably. A charge-compensation strategy of [Eu2+-Si4+] → [Cs+-P5+] could dramatically enhance the quenching concentration from 0.04 to 0.30, which is attributed to the decrease of Eu3+. Two cation-substitution strategies of larger Ba2+ (Sr2+) ions for Mg2+ ions could achieve superior emission adjustment of Eu2+ ions from the red to blue (yellow) region due to local lattice distortion. Interestingly, a consecutive emission adjustment from the red to blue region by simply changing the annealed temperature is reported for the first time, and the possible emission tuning mechanism is revealed based on a local lattice-strain control. This study could serve as a guide in developing Eu2+-activated ABPO4 phosphors with improving luminescence performance and controllable luminescence adjustment based on charge compensation and lattice-strain control through various cation substitutions.

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