Efficient energy transfer from Bi3+ to Mn2+ in CaZnOS for WLED application

Abstract

A series of Bi³⁺ and Mn²⁺ co-doped CaZnOS phosphors with a tunable emission color have been synthesized by a high temperature solid-state reaction method. Their crystal structure, spectroscopic properties, energy transfer and thermal quenching have been investigated systematically. An intense blue-green emission band at 485 nm and a red emission band at 616 nm were observed at an excitation wavelength of 375 nm, owing to the ³P_1,0 → ¹S₀ transition of Bi³⁺ and the ⁴T₁(⁴G) → ⁶A₁(⁶S) transition of Mn²⁺, respectively. The tunable color from blue-green, white light to red light can be obtained by varying the Mn²⁺ ion concentration from 0.005 to 0.015 in CaZnOS:Bi³⁺. The decay time decreased from 642 to 273 ns with the Mn²⁺ ion concentration x increasing from 0.005 to 0.015, and the energy transfer efficiency η_T can reach up to 65% in the CaZnOS:Bi³⁺,0.015Mn²⁺ phosphor. As the temperature increases from 300 to 420 K, the emission intensity is maintained at 67%, and the activation energy E_a is estimated to be 0.28 eV. An LED fabricated using CaZnOS:Bi³⁺,0.01Mn²⁺ exhibited the chromaticity coordinates and corrected color temperature (CCT) of (0.338, 0.364) and 4655 K, respectively. These results validate the promising applications of the CaZnOS:Bi³⁺,Mn²⁺ phosphor in UV white LEDs.