Site‐Selective Upconversion Luminescence of Ho³⁺ ‐Doped CaF₂ Crystals

Abstract

With red dye laser excitation, site-selective upconversion properties of three Ho3+ centres (C,,, C,,, and dimer) in CaF, : 0.1 at% Ho3+ crystals are studied. The energy level diagrams for the three centres are deduced from the spectral data. The excited state absorption from the 51, level plays a very important role in the upconversion coming from C,, and C3" centres, whereas the ground state absorption of 'I, dominates for that from the dimer centre. The upconversion of C,, and C,, centres is explained by a sequential two-photon excitation mechanism. For the dimer centre, the predominant upconversion mechanism is energy transfer.

Energy transfer upconversion in and doped crystals

“…The excitation spectra of the blue, green and red emissions show similar structure, indicating that the upconversion probably results from the energy transfer between paired Ho 3+ ions, whereas the successive absorption is less important. This phenomenon was also observed for the Ho 3+ dimer centres in CaF 2 and SrF 2 [16,17]. By comparing with the results observed in Ho 3+ doped CaF 2 and SrF 2 crystals, no single Ho 3+ C 3v , C 4v sites were recognized.…”

Yttrium Oxide Upconverting Phosphors. 5. Upconversion Luminescent Emission from Holmium-Doped Yttrium Oxide under 632.8 nm Light Excitation

“…[23][24][25] Measurements of upconversion energy transfer between Ho 3+ ions in YAG (Y 3 Al 5 O 12 ) have been reported 26 and only a small number of other papers refer to upconversion processes in Ho 3+ singly doped materials. [27][28][29][30][31][32][33][34][35][36] 2. Experimental Section 2.1.…”

“…In recent years upconversion lasing in Ho 3+ has been described by a number of authors. − Other methods of upconversion mechanisms have also been studied for Ho 3+ doped materials, in particular photon avalanche is one of the most efficient and complicated. It combines two phenomena, namely excited-state absorption (ESA) and cross-relaxation. , Photon avalanche has been observed in singly doped Ho 3+ lattices. − These reports have stimulated spectroscopic investigations of Ho 3+ in a number of host lattices for the purpose of ascertaining the properties necessary for laser action in the green region. − Measurements of upconversion energy transfer between Ho 3+ ions in YAG (Y 3 Al 5 O 12 ) have been reported and only a small number of other papers refer to upconversion processes in Ho 3+ singly doped materials. − …”

Upconversion luminescence of Ca1−xHoxF2+xand Sr0.98−xEr0.02HoxF2.02+xpowders upon excitation by an infrared laser

“…Upconversion materials are used for the visualization of infrared radiation. At present, there are a significant number of articles devoted to the investigation of upconversion luminescence of Ho 3+ in MF 2 (M = Ca, Sr, Ba, etc) crystals under excitation of 5 F 3 , 5 S 2 ( 5 F 4 ), 5 F 5 , 5 I 5 , 5 I 4 , 5 I 6 , and 5 I 7 levels [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Fluorite-type materials doped with rare-earth ions have specific features: low phonon energy and the tendency to form multiple cluster configurations of dopant ions [12,[21][22][23].…”