Promotion of efficiency and thermal stability by restraining dynamic energy migration based on the highly symmetric rigid structure in the n-UV excitation green emission garnet phosphors

Abstract

A series of Ca2YZr2−xHfxAl3O12:Ce3+ phosphors were synthesized via the high temperature solid state reaction. Crystal structure is analyzed using the Rietveld method based on the XRD pattern and the infrared absorption spectrum. All the samples are the garnet structures with the Ia3d space group. With the increase of the Hf4+ concentration, all the polyhedral structures become more symmetrical and compact. The structural variation causes the high-Hf4+ concentration compounds with a stronger rigidity and stability. The samples own a strong absorption at the near-UV regions, resulting in a good adaptation with the near-UV chips. Increasing the Hf4+ concentration, the low Ce3+ concentration doped samples exhibit similar emission spectra, however, the high Ce3+ concentration doped samples show an obvious blue shift. Based on the mechanism analysis from theoretical model, the excitation and emission spectra, decay data and the diffuse reflectance spectra, the emission position shift variation and different concentration quenching points could mainly be related with the different degree dynamic energy migration process. The rigid structure with a high symmetry for the high Hf4+ concentration samples could inhibit the energy migration between the Ce3+ ions. As the most important property parameters, the quantum efficiency and thermal quenching property both have obvious improvement when increasing the Hf4+ concentration. For Ca2YHf2Al3O12: 0.09Ce3+ samples, the quantum efficiency is 68.5%, and the intensity remains around 76.6% of the room temperature at 150 °C. In particular, our research highlights the significance of dynamical character and energy migration process on the photoluminescence property and provides the referential value for understanding the photoluminescence properties. The excellent properties show that the Ca2YHf2Al3O12: Ce3+ have potential as the green phosphors for application in near-UV excitation LEDs.