A study of negative-thermal-quenching (Ba/Ca)AlSi₅O₂N₇:Eu²⁺ phosphors

Abstract

An excellent color conversion material for high quality white LED with properties of negetive thermal quenching.

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

“…Therefore, the enhanced emission of NSPO:0.03Eu 2+ at higher temperature arisen from the Eu 2+ center and by an efficient energy transfer from electron-hole pairs (defects) to the Eu 2+ 5d-band, due to their close proximity to each other, which counteracts the usual emission loss due to non-radiative transition at high temperature. 53,54 2) Defect levels were embedded in the phosphor during the preparation process, and the energy transfer to Eu 2+ 5d band occurred with or without the involvement of the conduction band 55,57,58,60,63,64,66,[68][69][70][73][74][75][76][77] Most of the authors proposed that NTQ and/or ZTQ of the Eu 2+ -doped phosphor under investigation were due to the presence of defect levels, which were confirmed by the TL glow curve measurements. 55,57,58,60,63,64,66,[68][69][70][73][74][75][76][77] According to these authors, defect levels could be introduced into the lattice in the phosphor preparation process, by either a Eu 2+ ion aliovalently substituting for crystallographic sites of the host lattice, 55,57,58,[68][69][70] co-doping of a trivalent rare Earth ion in the lattice, 73,75 or size mismatch between Eu 2+ ion and the crystallographic sites Eu 2+ occupies.…”

“…53,54 2) Defect levels were embedded in the phosphor during the preparation process, and the energy transfer to Eu 2+ 5d band occurred with or without the involvement of the conduction band 55,57,58,60,63,64,66,[68][69][70][73][74][75][76][77] Most of the authors proposed that NTQ and/or ZTQ of the Eu 2+ -doped phosphor under investigation were due to the presence of defect levels, which were confirmed by the TL glow curve measurements. 55,57,58,60,63,64,66,[68][69][70][73][74][75][76][77] According to these authors, defect levels could be introduced into the lattice in the phosphor preparation process, by either a Eu 2+ ion aliovalently substituting for crystallographic sites of the host lattice, 55,57,58,[68][69][70] co-doping of a trivalent rare Earth ion in the lattice, 73,75 or size mismatch between Eu 2+ ion and the crystallographic sites Eu 2+ occupies. 63,66,76 The defects acted as electron traps that absorb and store the excitation light at low temperature.…”

“…68 In addition, Ma and co-workers reported the NTQ phenomenon from a cryogenic temperature to room temperature. 77 The degree of NTQ of the Eu 2+ -doped phosphors, i.e., the maximum emission intensity at a specific elevated temperature with respect to the value at room temperature, I max (T), varied from >100% for K 2 BaPO 4 F: 1.5% Eu 2+ 65 and Ba 0.975 La 0.005 Hf 0.995 Sc 0.005 Si 3 O 9 :0.02Eu 2+ 75 to 336% for LiBa 12 (BO 3 ) 7 F 4 : 1%Eu 2+ . 66 Moreover, the degree of NTQ for a given phosphor, e.g.…”

“…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.…”

Advancing Red-Emitting Fluoride Phosphors for Highly Stable White Light-Emitting Diodes: Crystal Reconstruction and Covalence Enhancement Strategy

“…White light-emitting diodes (WLEDs) find wide applications in solid-state lighting, liquid crystal display backlighting, and more. − The properties of red phosphors play a crucial role in determining the technical indicators of WLED devices, such as luminous efficacy (LE), color rendering index (CRI), color gamut, and overall stability. − However, several existing red-light material options present limitations in terms of light efficiency, stability, and complexity of preparation. Eu 2+ -doped nitrides, despite their wide red emission, suffer from a significant portion of the spectrum falling beyond the sensitivity range of the human eye, resulting in reduced light efficiency. , Red quantum dots like InP, CdSe, and perovskites exhibit poor stability and involve intricate preparation processes. − Eu 3+ /Mn 4+ -activated oxides, on the other hand, are challenging to excite with blue light. − In contrast, Mn 4+ -doped fluorides demonstrate effective excitation by blue light, possess a narrow emission spectrum (∼630 nm, aligning with the B.T.2020 display standard), high quantum efficiency (QE), and excellent thermal stability, making them a subject of widespread attention. , …”