Excellent enhancement of thermal stability and quantum efficiency for Na2BaCa(PO4)2:Eu2+ phosphor based on Sr doping into Ca

A novel bright cyan emitting phosphor of Eu2+activated Ba6BO3Cl9with robust thermal stability for full-spectrum WLED applications

“…The robust thermal stability is generally related with a large bandgap and high structural rigidity of the host lattice. 12,14 As mentioned above, BBC:Eu 2+ has a large bandgap of 5.98 eV based on the experimental result and 4.37 eV based on theoretical calculations, which is relatively large compared with other materials. In addition, the high rigidity plays important roles in luminescence efficiency and thermal stability.…”

“…However, due to the absence of red and cyan light, this variety of WLEDs has a poor R a (color rendering index) and a high CCT (correlated color temperature), making them unsuitable for indoor lighting applications. 5,[9][10][11][12] A simple and efficient approach has been put forward to optimize R a and CCT by adding additional red-emitting phosphors such as (Ca,Sr)AlSiN 3 :Eu 2+ , Sr 2 Si 5 N 8 : Eu 2+ , SrLiAl 3 N 4 :Eu 2+ , K 2 SiF 6 :Mn 4+ , and so on, but full spectrum WLEDs are still far from being achieved due to the existence of the cyan gap between the blue light and the green light. 13,14 In recent years, an alternative preparation method has been proposed to achieve WLEDs by coating tricolor RGB (red, green, and blue) phosphors on ultraviolet (UV) or nearultraviolet (n-UV) emitting LED chips, which can achieve a higher R a and lower CCT compared with blue light excited LEDs.…”

On The Validity of the Defect- Induced Negative Thermal Quenching of Eu2+-Doped Phosphors

“…The decay time of these Eu 2+ -doped phosphors was largely in a range from 0.2 to 2 μs at room temperature, which was in agreement with the typical lifetime reported for the 5d→4 f transition of Eu 2+ . 2,95 The decay time of 6.797 μs for Sr 3 SiO 5 :Eu 2+ ,Tm 3+ reported by Qiu 's team 73 Some phosphors had only one type of traps, 55,62,66 while others had two or three types of traps with different depths. 54,60,63,64,67,70,[74][75][76] Even for a phosphor with the same composition, e.g., Na 3 Sc 2 (PO 4 ) 3 :0.03Eu 2+ , trap depth reported by different authors was not identical.…”

“…Concerning the mechanism how defect levels transfer energy to the Eu 2+ 5d levels, some authors proposed that the energy transfer process occurred by a resonance mechanism following the radiative recombination of thermally released electron-hole pairs, 55,57,74,76 while other authors suggested that the detrapped electron was transferred directly to the Eu 2+ 5d levels, 66,75 or via the conduction band of the lattice to the Eu 2+ 5d levels, which compensates for the emission losses or thermal ionization of Eu 2+ ion. 60,[62][63][64]67,70,73 On the other hand, some authors did not specify clearly the mechanism of energy transfer from defect levels to the Eu 2+ 5d levels. 58,59,61,68,77 In addition, there were also other explanations for NTQ of Eu 2+ -doped phosphors, such as creation of defects due to cation disorder in Na 2 BaCa(PO 4 ) 2 :Eu 2+ , 62 phase transformation details of the host lattice for Na 3-2x Sc 2 (PO 4 ) 3 :xEu 2+ , 96 etc.…”

“…60,[62][63][64]67,70,73 On the other hand, some authors did not specify clearly the mechanism of energy transfer from defect levels to the Eu 2+ 5d levels. 58,59,61,68,77 In addition, there were also other explanations for NTQ of Eu 2+ -doped phosphors, such as creation of defects due to cation disorder in Na 2 BaCa(PO 4 ) 2 :Eu 2+ , 62 phase transformation details of the host lattice for Na 3-2x Sc 2 (PO 4 ) 3 :xEu 2+ , 96 etc.…”