Question

QUESTION 6 - Host Influence on Ln3+ Photoluminescence (8 pts) a) Describe the importance of the host in the host/dopant concept applied for Ln3t-based phosphors. Based on this, generally speaking, what type of host materials would be favoured? b) The upconversion emission spectra given below are obtained on the same type of Ln** ions, yet doped into two different host materials (both samples are excited with the same 980 nm excitation source and both samples are dispersed in the same solvent at comparable particle concentration). Describe the difference between both spectra and suggest a possible mechanism explaining the observed difference. PL intensity (a. u.) PL intensity (a. u.) 400 425 450 475 500 525 550 640 660 680 Wavelength (nm) 400 425 450 475 500 525 550 Wavelength (nm) 650 675

Answer 1

ISC IS ISC 3rd erited &and excited ist excited (660mm) Ln (111) Host-1 PL Intensity 525 550 660

An Hosty Energy. difference between the triplet state of Host (T) and the and E.s of lanthanide is possibly below 5000 cmt. Therefore 550 nm band is the most! intense. That means most of the meat excited state molecules are on the and excited state of the Lanthanide centre. Therefore most of the emission is oueurting from and Es of Ln (1) entre

ISES and E.S 3rd Eos 525 mm 980 nm Abs 660 mm 550 nm So In (1) Host-2 (9-)/ Intensil 660 525 350 um

In Host-2 The probable energy difference between the truflet excited state (T) of the ligand and the 3rd Es of Ln (11) centre is below 5000 cmt. This most the excited state molecules are sta on the 3rd E.S of ln (11) centre 4 starts emitting from that state. Therefore the intensity of 660nm band is highest in case of host-2.

sol-6 Lanthanide complexes with suitable host as coordinating, ligands are regarded as the As one of the best luminescent materials. This is mainly due to the characteristic narrow emission bands by the respective lanthanide metals. all the organic hosts do not have the ability to photo senestize the lanthanide centre. Only certain hosts can effectly transfer energy to the excited state of the lanthanide centre

ISC Si [ non-radiative Process Absorbance Iphosphorescence ligands Ln (11) So Singlet Ground state ISC = Inter system 4 = Firest Excited state Singlet T, Triplet Exciteal state. Only those types of hosts will be favoured which have the the trublet state energy more or less close the excited states of lanthanide centre. Crossing