Dopant Concentration Induced Optical Changes in Ca,Eu-α-Sialon

Abstract

Abstract:The phosphor powders of Ca (m/2)−x Eu x Si 12−(m+n) Al m+n O n N 16−n (m = 1.6, n = 0.8, x in the range of 0-0.08) were synthesized by means of a solid state reaction in flowing nitrogen in a carbon resistant furnace and the influence of Eu concentration on the crystal structure and photoluminescent properties was thoroughly studied. The optical properties of selected α-sialon:Eu 2+ samples at temperatures in the range of 10 to 500 K and pressures up to 240 kbar are presented. The crystal lattice parameters were affected by doping with europium and some increase of the unit cell volume was observed up to 6 mol % of Eu. The higher concentration of europium led to subtle changes in the overall structure of the produced sialon phosphors. It was shown that the chemical composition of Ca, Eu-α-sialon phosphor was slightly different from the designed one and the phosphor powders were contaminated by AlN. The phosphor particle surface showed significant europium and oxygen enrichment with Eu 3+ but below the thin surface layer Eu 2+ was dominant and higher nitrogen content was observed. After examination of absorption, excitation, and emission spectra it was found that the emission peak position shifted toward longer wavelengths with rising Eu 2+ concentration from 565 nm (0.1 mol % Eu 2+ ) to 585 nm (10 mol % Eu 2+ ). The quantum yield of the phosphors reached the maximum at a rather low concentration of 4 mol % of Eu. Excitation spectra depend on the monitored wavelength which is typical for multisite Eu 2+ . The existence of many Eu 2+ sites in the sample was supported by the dependence of the decay time on the monitored wavelength.

Optimization of Eu3+-to-Host Emission Ratio in Double-Perovskite Molybdenites for Highly Sensitive Temperature Sensors

“…The τ 1 and τ 2 of decay curves measured at room temperature are longer than at low temperature, and the longest component is not recorded at all. This confirms the origin of the persistent luminescence from defect states, which at room temperature efficiently feed the excited states of Eu 3+ …”

“…This confirms the origin of the persistent luminescence from defect states, which at room temperature efficiently feed the excited states of Eu 3+ . 32 The long decay component of Eu 3+ luminescence (see Figure 7f) is the longest for SMM with decay time equal 24 ms and the shortest for BMM with 10 ms. This luminescence is most likely to originate from the trapping states (defect states or other energy levels) within the bandgap, and the decay time is directly linked to their separation from the CB states.…”

Ho-SiAlON Ceramics as Green Phosphors under Ultra-Violet Excitations

“…XPS has been extensively used for the characterization of Si 3 N 4 -based thin films [ 25 , 26 ], powders [ 27 ], and sintered materials [ 28 ]. However, XPS studies on the hot-pressed α-SiAlON ceramics are limited [ 29 ].…”