Achieving white-light/tunable emissions via the controllable energy transfer in the single Ba9La2Si6O24:Eu3+,Bi3+ phosphor for UV converted white LEDs

Abstract Nowadays, ultraviolet (UV) and blue converted phosphors have played a key role in the solid-state lighting field, and the white light is usually produced by mixing multiple phosphors. In this work, we report a type of UV converted single white phosphor, i.e., Ba9La2Si6O24:Eu3+,Bi3+.Various techniques, such as powder X-ray diffraction (XRD), scanning electron microscopic (SEM), photoluminescence (PL) spectra, and quantum efficiency (QE), have been used to characterize the samples. In Bi3+ doped samples, upon excitation within the wavelength range of 250–380 nm can lead to three Bi3+ emission bands (i.e., 358 nm, 415 nm, and 516 nm), but only one emission band peaking at 415 nm appears when the excitation wavelength exceeds 380 nm. Structural analysis and discussion on the PL intensity variation reveal there are three Bi3+ luminescent centers at two different La3+ sites and one Ba2+ site. The Bi3+ concentration-induced luminescent quenching is dominated by the d-d interaction. In view of the spectral overlap between the Bi3+ emissions and the Eu3+ excitation spectra, the energy transfer from Bi3+ to Eu3+ of the Ba9La2Si6O24:Eu3+,Bi3+ is studied, and it is dominated by a dipole-quadrupole (d-q) interaction. Moreover, upon excitation at 365 nm, the emissions broadly tuning from blue, white and to red are achieved by varying the Eu3+ content. For the white Ba9La2Si6O24:Eu3+,Bi3+ sample, high temperature PL results show that it does not have severe degradation of emission intensity after increasing the temperature from 25 to 300 °C, exhibiting a good thermal stability. To show the potential application in the lighting fields, we fabricate a white light LEDs device by depositing this white phosphor on a 365 nm UV LED chip. As a result, the values, i.e., a color rendering index (CRI) of 95, luminous efficiency of 80 lm/W, and color temperature (CT) of ∼4215 K at chromaticity (0.382, 0.398), are achieved.