Tuning of the emission color via energy transfer from Bi~(3+) to Eu~(3+) ion in the Eu~(3+), Bi~(3+) doped calcium germanate phosphor for warm white LEDs

摘要

In the lighting field, it is essential to seek the phosphor materials with tunable emission for warm white light-emitting diodes (wLEDs). Herein, we reported a new type of Eu3+, Bi3+ doped calcium germanate phosphor, which can exhibit a broad emission tuning from blue, white and to red. According to the XRD results, the structure purity of all as-obtained germanate phosphors are revealed to feature a trigonal structure with the space group of R-3(No. 146). Structural analysis shows that the dopants of Eu3+ and Bi3+ should tend to substitute the Lu sites in the crystal host. The photoluminescence (PL) spectroscopy shows that the Eu3+ and Bi3+ ions can emit the blue emission and the red emission upon excitation at 297nm and 393nm, respectively. In view of the significant spectral overlapping between the excitation wavelength of Eu3+ and the emission wavelength of Bi3+, we study the energy transfer from Bi3+ and Eu3+ ion and reveal that the energy transfer is happened via an electric dipole-dipole (d-d) interaction. Remarkably, when the doping content of Bi3+ ions is fixed, changing the doping content of Eu3+ ions can induce the emission color tuning from blue, white and to red. To explain better the PL observation, a mechanistic pattern, which bases on the energy transfer from Bi3+ and Eu3+ ion, has been also constructed, which is expected to provide a general idea for achieving the energy-transfer-controlled tunable phosphor materials for phosphor-converted wLEDs.