Single crystal growth and cold white light application of Dy,Tb:CaWO4 crystals

Abstract

We report the Dy:CaWO₄ and Dy,Tb:CaWO₄ crystals grown by the Czochralski method, and their structural and optical properties are studied. Raman spectra, polarization absorption spectra, polarization emission spectra, and fluorescence lifetime are obtained. The Judd–Ofelt intensity parameters (Ω_t, t = 2, 4, 6), the fluorescence branching ratios, and the radiative lifetimes of the ⁴F_9/2 level are calculated based on the Judd–Ofelt theory. The emission cross-sections are calculated using the Füchtbauer–Ladenburg method, showing large emission cross-sections at 573 nm: 9.86 × 10⁻²¹ cm² (π polarization) and 8.11 × 10⁻²¹ cm² (σ polarization) for Dy:CaWO₄, and 9.09 × 10⁻²¹ cm² (π polarization) and 7.69 × 10⁻²¹ cm² (σ polarization) for Dy,Tb:CaWO₄, respectively. In addition, under 450 nm excitation, the crystals emit ideal white light, with CIE coordinates (0.3258, 0.3191) and a correlated color temperature of 6000 K. Therefore, Dy:CaWO₄ and Dy,Tb:CaWO₄ crystals are promising materials for white light-emitting diode (LED) applications.