Sensitization of Mn2+ luminescence via efficient energy transfer to suit the application of high color rendering WLEDs

Abstract

Developing novel luminescent materials with ideal properties is an endless project, urged by growing requirements of advances in energy saving, healthy lighting and environmental friendliness. Herein, a series of ScCaOBO₃:Ce³⁺,Mn²⁺ phosphors with excellent luminescence properties were synthesized by the high temperature solid state method. X-ray diffraction was applied to analyse the phase composition of the obtained phosphors. The morphology and dopant distribution were observed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS), respectively. The Rietveld refinements and luminescence spectra indicate that Ce³⁺ preferentially occupies the Sc³⁺ site and produces a blue emission band at around 460 nm, which originates from the characteristic 5d–4f transitions, while Mn²⁺ preferentially occupies the Ca²⁺ site and emits red light due to its characteristic ⁴T₁(⁴G)–⁶A₁(⁶S) transitions. Upon excitation at 354 nm, both Ce³⁺ and Mn²⁺ emissions can be obtained and further investigations evidenced that the broad and intense light emission of Mn²⁺ located in the red spectral region is the result of energy transfer from Ce³⁺ to Mn²⁺. Theoretical calculations reveal that the energy transfer process from Ce³⁺ to Mn²⁺ is of the resonance type and is governed by electric dipole–dipole interactions. Since the ScCaOBO₃:Ce³⁺,Mn²⁺ phosphors are capable of producing broadband emissions that widely cover the blue and red spectral regions, the introduction of a green light-emitting phosphor CMA:Tb³⁺ can conveniently generate high quality white light. Therefore, a white light-emitting diode device with extremely high color rendering indices, R_a = 93.7 and R₉ = 91.9, was successfully obtained.