Calcium selenide has the molecular formula of CaSe
and the molecular weight of 119.0452 g/mol. Its CAS
number is 1305-84-6. It is a white to brown cubic crystal
with a melting point of 1408°C (where it decomposes, in
air, to CaO and SeO2). Its density is 3.81 g/cm3 and it is
unstable in air or moisture. Its refractive index is 2.274.
Because of its instability in the presence of water, it
cannot be prepared in an aqueous solution.
CaSe can be prepared by the reaction of calciumoxide
and selenium:
CaO(solid)+ Se(solid)+ heat ? CaSe(solid)+ SeO2(gas)
Alternately, the two elements can be reacted together
to form the selenide:
Ca(solid)+ Se(solid)+ heat ? CaSe(solid)
In the first reaction, Se melts at 225°C while the CaO
is stable. Selenium dioxide sublimes at 320°C. The reaction
is carried out in an inert atmosphere at about
550°C. If a tube furnace is used, crystals of SeO2 appear at the cool end of the tube. In the second reaction, an inert atmosphere is mandatory and the reaction temperature
is also 550°C (which is below the melting point of
Ca metal). However, the reaction does not go to completion
and only about 50% of theoretical CaSe is formed.
To achieve close to 100% reaction, the selanate can be
reduced to form CaSe:
CaSeO4+H2+ heat ? CaSe+H2O
용도
The major usage of CaSe has been as a phosphor.
Lenard and Pauli first described this phosphor, CaSe:-
Sm3+
, as an infrared stimulable material about 100 years
ago. CaSe:Ce3+
is a blue-emitting (～4500? ) phosphor.
However, due to its instability, CaSe was never used in
the lighting industry. More recently, it has been combined
with the strontium compound to form phosphors.
(Ca1-x,Srx)Se:Eu2+
, which is an efficient red-emitting
phosphor, was prepared by solid-state reaction at high
temperatures in CO atmosphere. These phosphors can
be excited efficiently by visible light from 430 to
490 nm and emit red light with broadband excitation
from blue LED chips. If the Sr/Ca ratio is decreased,
the lattice parameters get smaller, and the emission
wavelength shows a red shift. A suitable wavelength
can be obtained by adjusting the Sr/Ca ratio. Because
of the commercial afterglow exhibited by calcium
sulfide phosphor, these synthesized phosphors have
higher emission efficiency and are a good choice for
manufacturing white LED lamps. These phosphors are
promising candidates for emitting red light for LEDs.
When mixed with a green phosphor on a InGaN-based
blue chip, the as-synthesized red phosphors generated
white light for LEDs.
