1：Experimental Design and Method Selection:

A series of Sr2-xAl3EuxO6F (x =

2：00, 01, 03, 05, 07 and 10) phosphors were synthesized via conventional solid-state reaction route. Pure SrCO3 (8%), Al2O3 (≥ 6%), SrF2 (99%), and Eu2O3 (999%) purchased from Sigma-Aldrich were used. Stoichiometric contents of starting materials excluding slightly excessive SrF2 (5 wt%) were meticulously grounded. The resultant grounded mixture was then transferred to an alumina cup crucible and fired in the air at 1250?C for 4 hrs. The Sr8Al3O6F:

Ba

3：1/Eu1 sample was also prepared by employing a similar method wherein BaCO3 (8%) was used as a Ba2+ source. Sample Selection and Data Sources:

The X-ray diffraction (XRD) characteristics of synthesized materials were measured using Ni filtered Cu-Kα (λ =

4：54 ?) at 45 kV and 40 mA via Philip’s x’pert pro diffractometer. List of Experimental Equipment and Materials:

The electronic structure of Sr2Al3O6F was estimated using the DFT modelling. The Raman spectrum of the undoped Sr2Al3O6F was collected from a Confocal Raman Microscope (alpha 300 R WITEC Germany). The UV-Vis diffused reflectance spectra (DRS) were recorded using Shimadzu UV

5：The photoluminescence (PL) characteristics were measured using a YvonFluorolog 3 spectrofluorimeter with a 450W Xenon flash lamp as the exiting source. The XPS scans were carried out using Omicron ESCA+, Oxford Instruments Germany. Experimental Procedures and Operational Workflow:

36 The color coordinates of Commission Internationale de I’Eclairage (CIE) were estimated via a color calculator software. The white-LED modules were fabricated by mixing the optimal ratio of red phosphor with the Y3Al5O12: Ce3+ yellow phosphor. This mixture was then dispersed in transparent silicon resin for making the phosphor blend which was pasted on a 460?nm blue InGaN LED chip, which was operated at 300 mA current. The PL properties of the fabricated LEDs were measured using a CCE spectrophotometer (OCEAN-FX-XRI-EX).

6：Data Analysis Methods:

The band structure was calculated to study the electronic structure of Sr2Al3O6F. The pDOS (projected density of states) and total DOS (density of states) were also calculated. The various radiative properties of the emission bands were analyzed through the Judd-Ofelt theory.