Excitation wavelength dependent color tunability, white light generation and enhanced optical emission in mixed phase ZnO–CAZO:xEu³⁺ over single phase ZnO:xEu³⁺ phosphors: a comparative study

Abstract

Mixed phase ZnO-CAZO:xEu3+ phosphors have been synthesized by solid state reaction method to get tunable light including white light under excitation with different wavelengths. The XRD, SEM, FTIR, UV–vis absorption, photoluminescence excitation and emission spectra of the samples and the lifetime of 5D0 level of Eu3+ ions have been studied. The ZnO phosphor has well known hexagonal structure, whereas Ca3Al4ZnO10 (CAZO) has orthorhombic structure. The UV–vis spectral studies show that the materials have wide band gap. The excitation spectra of ZnO-CAZO:xEu3+ phosphors with λ em = 613 nm show broad bands at 270 and 370 nm alongwith discrete peaks due to Eu3+ ion. An excitation with 370 nm of ZnO-CAZO:xEu3+ phosphors results a broad continuum from 400–700 nm with maxima at 520 nm. The excitation with 270/394 nm on the other hand gives intense discrete peaks due to Eu3+ ion alongwith broad host emission. However, on excitation with 467 nm, it gives intense red emission with CIE coordinates (0.64, 0.36) and color purity 90%. The emission intensity is maximum for ZnO-CAZO:1.5Eu3+ phosphor. The excitation with 394 nm, results white light for ZnO-CAZO:0.5Eu3+ phosphor with CIE coordinates (0.34, 0.35), which is almost equal to the ideal white light coordinates (0.33, 0.33). The emission intensity in the mixed condition (ZnO-CAZO:1.5Eu3+) is 4.94 times greater than its single (ZnO:1.5Eu3+) phase under 370 nm excitation.

Intense photoluminescence in CaTiO3:Sm3+ phosphors, effect of co-doping singly, doubly and triply ionized elements and their applications in LEDs

“…The color purity of the phosphor materials is another important parameter to recognize phosphor as a good source of light for a particular color for solid-state lighting applications. The color purity of the light source can be calculated using the following relation: 43 where ( x , y ) are the CIE coordinates of the phosphor, ( x d , y d ) are the CIE coordinates of the dominant wavelength and ( x i , y i ) are the CIE coordinates for the standard light source. The values of color purity in the present case were found to be 87.80% for CaTiO 3 :2Sm 3+ , CaTiO 3 :2Sm 3+ /5.0K + , CaTiO 3 :2Sm 3+ /5.0Ba 2+ and CaTiO 3 :2Sm 3+ /5.0Bi 3+ phosphors and 89.88% for CaTiO 3 :2Sm 3+ /5.0Mg 2+ and CaTiO 3 :2Sm 3+ /0.5Gd 3+ phosphors.…”

“…We have also calculated the correlated color temperature (CCT) to evaluate the nature of emitted light. The CCT values for the different phosphor samples were evaluated using McCammy's equation as follows: 43 T = −449( n 3 ) + 3525( n 2 ) − 6823.3( n ) + 5520.33 where n = ( x − 0.3320)/( y − 0.1858) and ( x , y ) refer to CIE coordinates. The calculated CCT values were found to be 1975 K, for CaTiO 3 :2Sm 3+ , CaTiO 3 :2Sm 3+ /5.0K + , CaTiO 3 :2Sm 3+ /5.0Ba 2+ and CaTiO 3 :2Sm 3+ /5.0Bi 3+ phosphors and 1880 K CaTiO 3 :2Sm 3+ /5.0Mg 2+ and CaTiO 3 :2Sm 3+ /0.5Gd 3+ phosphors.…”

“…The color purity of the light source can be calculated using the following relation: 43 Color purity…”