Spectroscopic, optical properties and ab-initio calculation of thermally stable Na2Ca1-xP2O7:xEu3+ phosphors for wLEDs

A series of Na2Ca1-xP2O7:xEu3+ phosphors (x = 0.01–0.1) were synthesized via solid-state reaction route. The phase purity and crystal structure were confirmed via XRD and Rietveld refinement analysis. Density functional theory (DFT) calculations and experimental analysis were utilized simultaneously to study the electronic and optical properties. The phosphors emit the typical Eu3+ ions emissions associated with the f-f transitions when excited at 394 nm. Energy transfer with the nearest neighbor or next nearest neighbor dopants caused the concentration quenching in present phosphors. To confirm the Eu3+ ion's local symmetry characteristics, the optical transition parameters were calculated using the Judd-Ofelt theory. Furthermore, the thermal stability was explored in depth. The temperature-dependent photoluminescence (PL) emission spectra of the developed phosphors showed excellent thermal stability (90.63%) at 423 K and the calculated activation energy was 0.26 eV. Moreover, the Na2Ca1-xP2O7:xEu3+ phosphors were mixed with commercial green-blue emitting and coated over a NUV chip to fabricate the wLED. The findings indicate that Eu3+ activated Na2CaP2O7 phosphors are potential wLED materials.