Effect of Charge Compensation on the Photoluminescence and Thermal Stability of Trivalent Samarium-Doped Calcium Barium Phosphate Phosphors

Abstract

A series of Ca6BaP4O17:Sm3+ phosphors without or with different charge compensation approaches (co-doping Li+ or Na+ ions) were synthesized by using a conventional solid-state reaction method. The crystal structure and morphologies of the phosphors were investigated by using X-ray diffraction pattern and scanning electron microscope after synthesizing the phosphor, respectively. The luminescence and spectral properties were studied by photoluminescence and diffuse reflectance spectroscopy. By introducing the charge compensator alkali metal ions A+ (A = Li and Na) into the lattice of Ca6BaP4O17:Sm3+ phosphor, its emission intensity can be enhanced. The phosphors under 405 nm excitation show characteristic emission of Sm3+ ion with the main orange–red peak centered at 602 nm. The results suggested that the Li+ ion is a good charge compensator in Ca6BaP4O17:Sm3+ phosphors due to its enhancement in luminescence and as a flux for improving the morphology of phosphors. The calculated CIE coordinates and color purity of phosphors with charge compensation of optimal Li+ ions co-doping concentration are (0.6090, 0.3892) in the orange–red region of the spectrum and ∼ 99.5% under 405 nm excitation. Besides, the thermal stability of proposed samples can be improved from 84% to 93% which is pretty high compared with published data. The mechanism is detailed in this paper.

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

“…115 Similar phenomena that both the QE and thermal stability of the phosphor could be improved by eliminating the defects via introduction of a suitable charge compensator were reported by a couple of independent researchers. [116][117][118][119] On contrary to the anti-defect strategy for improving QE and thermal stability of the phosphor, a considerable number of papers have been published reporting defect-induced NTQ of WLED phosphors. Based on the observations that measured integrated emission intensity of the phosphor increased with increasing temperature (NTQ) along with that TL experiment of the phosphor confirmed the presence of defects, these authors claimed that NTQ of the phosphor stemmed from thermally stimulated energy transfer from defects to excited state of the activator, irrespective of the emission arising from a d → f or f→f transition of a rare Earth ion or a d→d transition of a transition metal ion.…”