Luminescence of emission-tunable Ca10Li(PO4)7:Eu2+, Sr2+, Mn2+ phosphors with various Eu2+ centers for LED applications

Ca10Li(PO4)7:Eu2+, Sr2+, Mn2+ (CLP:Eu2+, Sr2+, Mn2+) phosphors were prepared by solid-state reaction method, and their photoluminescence properties were investigated. The phase purity was examined by XRD patterns; the optical bandgaps of the host materials were determined to be about 5.35 eV from the diffuse reflection spectra. The Eu2+ single-doped CLP exhibits several overlapping emission bands which are derived from various Eu2+ centers, and the excitation spectra are broadened and enhanced gradually with increasing either monitoring wavelength or Eu2+ concentration. When the Sr2+ ions are doped into CLP:Eu2+, the excitation bands are further extended in width and increased in intensity, which make the CLP:Eu2+ more suitable for the LED chips. Correspondingly, the emission spectra show a continuous enhancement for long-wavelength emissions, accompanied by a gradual decay for short-wavelength emissions. These observations could be due to the adjustment of the crystal structure by introducing Sr2+ ions into CLP which further affects the spectral features. In the CLP: Eu2+, Sr2+, Mn2+ system, warm white emission was obtained with low correlated color temperature. In sum, multi-color-emitting CLP:Eu2+, Sr2+, Mn2+ phosphors were developed by adjusting the dopants contents, and the above results indicate their potential applications in LEDs.