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The white-light-emitting devices (WLEDs) for urban ecological lighting remain the challenge. The current urban lighting system destroys the growth habits of plants and leads to inhibition of plant growth, reduced branching, smaller leaf area and reduced total dry weight due to excessive blue light. In this work, a series of blue-green and red dual-emission Na 3 Ba 2 Ca(PO 4) 3 :Eu2+, Mn2+ phosphors have been successfully synthesized by the high-temperature solid-state reaction method. The crystal structure, the occupancy of the dopant ions and the luminescence characteristics were carefully investigated. The excitation and emission spectra as well as the decay lifetime confirm the effective energy transfer from Eu2+ to Mn2+, which leads to a tunable luminescence with greatly reduced blue emission. Especially, the optimal Na 3 Ba 2 Ca(PO 4) 3 :0.02Eu2+, 0.11Mn2+ phosphor demonstrates a high internal quantum yield of 99.7%. At 150 °C, the luminescence intensity of Na 3 Ba 2 Ca(PO 4) 3 :0.02Eu2+, 0.11Mn2+ can maintain 64.5% of room temperature intensity. In addition, the WLED device fabricated with Na 3 Ba 2 Ca(PO 4) 3 :Eu2+, Mn2+ phosphor shows white light emission with CIE coordinates of (0.3800, 0.3852), rendering index (Ra) of 65.4 and correlated color temperature (CCT) of 3640 K. These results confirm that the Na 3 Ba 2 Ca(PO 4) 3 :Eu2+, Mn2+ phosphor can be applied as a white light source in the urban ecological field. [Display omitted] • Tunable white Na 3 Ba 2 Ca(PO 4) 3 :Eu2+,Mn2+ were synthesized for the first time. • Occupancy of dopant ions in the matrix is fully analyzed. • The conversion mechanisms are described as cooperative energy transfers from Eu2+ to Mn2+. • The Na 3 Ba 2 Ca(PO 4) 3 :0.02Eu2+,0.11Mn2+ owns high internal quantum yield and urban ecological lighting. • This phosphor can be applied as a white light source in the urban ecological field. [ABSTRACT FROM AUTHOR]

High thermal stability and quantum efficiency are the two very significant factors for phosphors when concerning all kinds of related applications. Therefore, it is still main research topics as long as referencing to the luminescence phosphors. It is well known that deep trap and large band gap are beneficial to excellent thermal stability. In this work, a series of Na 2 BaCa 1- x Sr x (PO 4) 2 :0.03Eu2+ phosphors have been prepared by traditional solid state reaction. When the Sr2+ content increases, the emission intensity exhibits a blue shift phenomenon with the highest peak around 448 nm caused by the varied centroid shift (ε c) and the crystal field splitting (ε cfs). The thermal stability of Na 2 BaCa 0.2 Sr 0.8 (PO 4) 2 :0.03Eu2+ phosphor still approaches to 100.3% of that room temperature at 150 °C, while the external and internal quantum efficiency are greatly enhanced from 19.92% to 62.53%. It is due to the effect of the cation disorder by introducing the high level of Sr ion, which create the deep trap and broaden the bandgap, resulting in the anti-thermal quenching behavior and enhanced quantum efficiency. Moreover, Rietveld refinements, microstructure, decay curves and thermoluminescence are also adopted to shed light on related mechanism of luminous performance. Furthermore, a pc-WLED device has been fabricated through Na 2 BaCa 0.2 Sr 0.8 (PO 4) 2 :0.03Eu2+ blue phosphor mixed with commercial yellow phosphor (SrSi 2 O 2 N 2 :Eu2+) and red phosphor (Sr 2 Si 5 N 8 :Eu2+), which performs a color temperature of 4721 K with a high color rendering index of Ra = 91.9. In view of zero thermal quenching and favorable quantum efficiency, this new phosphor is a prospect candidate for blue phosphors in WLED application. Further, the work provides a new method and reference for the great enhancement of thermal stability and quantum efficiency of luminescence materials. Based on the crystal structure of Na2BaCa(PO4)2:Eu2+ phosphors, the PL, thermal dependent spectra and application in WLED of Na2BaCa0.2Sr0.8(PO4)2:Eu2+ phosphors have been detected. [Display omitted] • A series of solid solution Na 2 BaCa x Sr 1 -x (PO 4) 2 (x = 0–1.0) have been synthesized. • The thermal stability of Na 2 BaCa 0.2 Sr 0.8 (PO 4) 2 :0.03Eu2+ is 100.3% of that room temperature at 150 °C. • The external quantum efficiency of Na 2 BaCa 0.2 Sr 0.8 (PO 4) 2 :0.03Eu2+ is improved from 19.92% to 40.78%. • The fabricated white WLED shows the CIE of (0.3532, 0.3561), the CCT of 4721 K and CRI of 91.9. [ABSTRACT FROM AUTHOR]

Ce3+ doped CaAlSiN 3 is a promising broadband orange phosphor that can be applied in white light-emitting diodes (wLEDs) solid state lighting for general illumination. However, its emission color and quantum efficiency are not good enough to achieve high color rendering properties and luminous efficacy of wLEDs. In this work, we proposed to realize the spectral tuning and property enhancement of CaAlSiN 3 :Ce3+ by bandgap engineering via the cationic substitution of Ca by Sr. The relationship between photoluminescence and local coordination structure as well as electronic structure were revealed. The substitution led to a blue-shift in emission maximum by 13 nm (from 595 to 582 nm) and a highest external quantum efficiency of 55% (enhanced by 10%). This broadband yellow phosphor enabled to produce wLEDs with a color rendering index of 83.3, luminous efficacy of 114.6 l m/W and a color temperature of 4604 K. With the substitution of Ca by Sr in broadband yellow phosphor CaAlSiN 3 :Ce3+, a blue-shift in the emission maximum (from 595 to 582 nm) was attained, while the quantum efficiency and thermal stability of the phosphor containing 40% Sr were increased by 10 and 7.2% due to the decreased crystal field splitting and increased bandgap of the host. Image 1 • The bandgap engineering was adopted to realize the spectral tuning of CaAlSiN 3 :Ce3+ via the substitution of Ca by Sr. • The relationship between local structure and luminescence properties in Sr x Ca 1-x AlSiN 3 :Ce3+ was comprehensively discussed. • With the substitution, a blue-shift in the emission maximum (from 595 to 582 nm) was attained. • The quantum efficiency and thermal stability of the sample containing 40% Sr were raised by 10 and 7.2%, respectively. • This broadband yellow phosphor enabled to produce wLEDs with a color rendering index of 83.3. [ABSTRACT FROM AUTHOR]