Christine Reinhard

Upconversion phenomena in the Yb3+ doped transition metal compounds Rb2MnCl4 and CsMnBr3

Abstract Crystals of Yb 3+ doped Rb 2 MnCl 4 and CsMnBr 3 show orange–red Mn 2+ 4 T 1 g → 6 A 1 g upconverted luminescence under near-infrared Yb 3+ excitation. By short 10 ns pulse excitations the upconversion (UC) process for both compounds has been determined to consist of a sequence of ground and excited-state absorption steps. This mechanism can gain nonzero probability by assuming an exchange mechanism between Yb 3+ and Mn 2+ . The efficiency of the UC process is dependent on the structural nature of the Yb 3+ –Mn 2+ connection. It is three orders of magnitude more efficient in Rb 2 MnCl 4 : Yb 3+ with a corner-sharing Yb 3+ –Cl–Mn 2+ arrangement than in the face-sharing Yb 3+ –Br 3 –Mn 2+ arrangement of CsMnBr 3 : Yb 3+ .

Cooperative radiative and nonradiative effects in K2NaScF6 codoped with V3+ and Er3+

K2NaScF6 crystals codoped with V3+ and Er3+ exhibit some novel cooperative near-IR to visible upconversion processes at cryogenic temperatures. V3+ mainly acts as a broadband sensitizer. The V3+ 3T1g --> 3T2g excitation between 13,500 and 15,500 cm(-1), after fast relaxation to V3+ 1T2g, can be transferred to Er3+ 4I(11/2), and then upconversion takes place. Four upconversion mechanisms are identified and characterized. For narrow-band laser excitation the overall efficiency of the upconversion processes is low. However, at 12 K for broadband excitation, such as in a lamp, between 12,000 and 14,500 cm(-1) the number of emitted visible photons is roughly doubled by codoping V3+ in addition to Er3+.

Cooperative processes in Pr3+ and V3+ codoped Cs2NaScCl6

Abstract A crystal of Cs 2 NaScCl 6 codoped with Pr 3+ and V 3+ was synthesized and studied by high-resolution optical spectroscopy. The principal objective is the search for a material containing a broad-band absorber in the near-IR which is able to sensitize a near-IR to visible upconverter. V 3+ in a chloride environment does absorb in the near-IR. However, the V 3+ to Pr 3+ energy-transfer step is extremely inefficient in the title compound. Nevertheless we were able to identify and characterize a new type of upconversion process.