Synthesis, Photoluminescent Characteristics and Eu3+-Induced Phase Transitions in Sr3Zr2O7:Eu3+ Red Phosphors

Designing phosphors that are excited by blue light is extraordinarily important for white light-emitting diodes (w-LEDs). In the present study, a new Ruddlesden-Popper type of SZO:xEu3+ (x = 0.01~0.10) phosphors was developed using solid-state reactions. Interestingly, a Eu3+ doping-induced phase transformation from the Sr3Zr2O7 (cubic) to the SrZrO3 (orthorhombic) phase was observed, and the impact of the occupied sites of Eu3+ ions on the lifetime of Sr3Zr2O7:xEu3+ phosphors is discussed in detail. Diffuse reflectance spectroscopy results showed that the band gap of SZO:xEu3+ phosphors gradually increased from 3.48 eV for undoped Sr3Zr2O7 hosts to 3.67 eV for SZO:0.10Eu3+ samples. The fluorescence excitation spectrum showed that ultraviolet (300 nm), near-ultraviolet (396 nm) and blue light (464 nm) were all effective excitation pump sources of Sr3Zr2O7:xEu3+ phosphors, and the strongest emission at 615 nm originated from an electric dipole transition (5D0→7F2). CIE coordinates moved from orange (0.5969, 0.4267) to the reddish-orange region (0.6155, 0.3827), and the color purity also increased. The fabricated w-LED was placed on a 460 nm chip with a mixture of YAG:Ce3+ and SZO:0.1Eu3+ samples and showed "warm" white light with a color rendering index (CRI) of 81.8 and a correlation color temperature (CCT) of 5386 K, indicating great potential for application in blue chip white LEDs.