Modification of luminescence spectra of CaF₂: Eu²⁺

Abstract

CaF2:Eu(2+) is a well known phosphor having efficient excitation in the near ultraviolet (NUV) range. Phosphors with NUV excitation are required in newly emerging applications such as photoluminescence liquid crystal displays (PLLCD), solid-state lighting (SSL), and down-conversion for solar cells. However, emission of CaF2:Eu(2+) is around 424 nm. Eye sensitivity drops considerably at these wavelengths. It is thus not useful for display applications for which emission in one of the primary colours (blue - 450 nm, green - 540 nm or red - 610 nm) is required. Efforts were made to modify the Photoluminescence (PL) spectra of CaF2:Eu(2+) to meet these requirements using co-dopants. A Ca0.49 Sr0.50 Eu0.01 F2 phosphor showing better colour coordinates and having an emission maximum around 440 nm was discovered during these studies.

Effect of redox reactions on the thermoluminescence characteristics of Cu-doped NaLi2PO4 phosphors

“…, beyond 600 °C) could be attributed to diffusion of atmospheric oxygen leading to more complex defects at the impurity ion sites as well as redox reactions. 32,40…”

“…For this, samples were placed in alumina crucibles and covered using ceramic wool under a steel net and another alumina crucible one above the other and upside down (in order to avoid contamination of the sample with the ne charcoal powder while heating). 32,33 These crucibles were then placed inside a closed charcoal box. Burning of the charcoal under scarcity of oxygen produces CO/CO 2 gas as reducing atmosphere.…”

“…32,40 It is known that aer heat treatments above 250 °C, the ratios of TL emissions 380 and 350 nm corresponding to Cu 2+ and Cu + in Cu-doped LiF, respectively, in the samples annealed at different temperatures decrease; this has been attributed to the Cu + / Cu 2+ + e − conversions during heating treatments. 32,40 such redox reactions could also occur in reverse order, i.e., Cu 2+ + e − / Cu + . 30 We strongly believe that such conversions must be taking place in our Cu-doped NaLi 2 PO 4 materials also.…”

The Bridgman method growth and spectroscopic characterization of calcium fluoride single crystals

“…These centers perhaps could be created by oxygen defects within the host of CaF 2 . However, the occurrence of defects in crystal is very rare compared to the nanostructures described in [42], so the luminescence of our sample is very weak compared to the luminescence of structure described in [42]. To obtain good luminescence response, the samples of CaF 2 are doped with Ag, Eu, Tb, Cu or Dy [42,43].…”

“…However, the occurrence of defects in crystal is very rare compared to the nanostructures described in [42], so the luminescence of our sample is very weak compared to the luminescence of structure described in [42]. To obtain good luminescence response, the samples of CaF 2 are doped with Ag, Eu, Tb, Cu or Dy [42,43]. However, CaF 2 crystal is usually used in applications where high optical transmission is needed and photoluminescence is not desirable characteristics [44].…”